The objective with synthetic multifunctional nanoarchitecture is to create large suprastructures with interesting functions. For this purpose, lipid bilayer membranes or conducting surfaces have been used as platforms and rigid-rod molecules as shape-persistent scaffolds. Examples for functions obtained by this approach include pores that can act as multicomponent sensors in complex matrices or rigid-rod π-stack architecture for artificial photosynthesis and photovoltaics.

Gold particles covered with 1,1′-binaphthyl-2,2′-dithiol (BINAS) were prepared. Using size exclusion chromatography, it was possible for the first time to separate the sample into fractions with different sizes and colors. Transmission electron microscopy shows that the particles are very small, in the order of 1 nm or slightly above. The absorption spectra of the separated samples show rich structure. The particles show size-dependent optical activity in metal-based electronic transitions. The shape of both the absorption and circular dichroism spectra of one of the smallest fractions exhibits similarities with the spectra reported for Au₁₁ covered by 2,2′-bis(diphenylphosphino)-1,1′-biphenyl although the spectra are shifted to shorter wavelengths in the case of the dithiol. The anisotropy factors, Δϵ/ϵ of these particles are as large as 4 × 10⁻³, which is larger than the values reported for gold particles stabilized by phosphines and water-soluble thiols. This indicates that BINAS is particularly well-suited to impart chirality on to gold particles.

A combination of in situ attenuated total reflection infrared (ATR-IR) spectroscopy, UV−vis spectroscopy and transmission electron microscopy was used to study the adsorption of thiol-protected gold nanoparticles on TiO₂ films and the behavior of the resulting composite films upon UV irradiation. The gold nanoparticles were covered by charged thiols N-acetyl-l-cysteine and l-glutathione and had a mean core diameter of about 1 nm. The TiO₂ film was prepared by deposition of a slurry of TiO₂ nanoparticles with a particles size of 21 nm. The combination of the two spectroscopic techniques showed that the adsorption of the gold nanoparticles onto the TiO₂ films is significantly limited by intrafilm diffusion. Upon illumination the IR spectra revealed the removal of the adsorbed thiolates and the appearance of sulfates. These species were also observed when N-acetyl-l-cysteine adsorbed on TiO₂ was illuminated, i.e., in the absence of gold. In the latter case oxalate was observed in large quantity on the TiO₂ surface, in contrast to the illumination of the N-acetyl-l-cysteine-protected gold particles. This indicates a different pathway for the decomposition of the adsorbed thiol when adsorbed on the gold or directly on the TiO₂ surface. In situ UV−vis spectroscopy also shows the formation of larger particles upon illumination, which is confirmed by transmission electron microscopy.

Using simple organic synthetic transformations, a novel diazaoxatricornan derivative, the 12c-methyl-12-phenyl-8-propyl-12,12c-dihydro-8H-4-oxa-8,12-diazadibenzo[cd,mn]pyrene (6a), was prepared. This novel chiral cup-shaped molecule was isolated in racemic form and in excellent yield after the addition of methyl lithium to the BF₄ salt of a novel unsymmetrical diazaoxatriangulenium cation. Compound 6a was found to be stable under classical laboratory conditions—something not obvious considering the extreme stability of the carbenium ion precursor, the electron-rich nature of the core, and the strain induced by the pyramidalization of the central carbon. The enantiomers were readily separated by chiral stationary phase chromatography, and the absolute configuration of (−)-(S)-6a was determined by a comparison of the experimental and theoretical vibrational circular dichroism (VCD) spectra. This isolation of (−)-(S)-6a and (+)-(R)-6a constitutes thus the first report of a nonracemic closed-capped chiral bowl molecule for which the chirality is due to the intrinsic dissymmetry of the central core of the structure only.

The thiolate-for-thiolate ligand exchange was performed on well-defined gold nanoparticles under an inert atmosphere without any modification of the core size. This reaction is faster than the well-known core etching. Surprisingly, if a chiral thiol is exchanged for its opposite enantiomer, the optical activity in the metal-based electronic transitions is reversed although the form of the CD spectra remains largely unchanged. The extent of inversion corresponds to the overall ee of the chiral ligand in the system. This shows that the chiral arrangement of metal atoms in the metal particle (surface) can not withstand the driving force imposed by the ligand of opposite absolute configuration. If the incoming thiol has a different structure, the electronic transitions in the metal core are slightly modified whereas the absorption onset remains unchanged. These results emphasize the influence of the thiols on the structure of the gold nanoparticles and give insight on the ligand exchange pathways.

Modulation excitation spectroscopy (MES) allows sensitive and selective detection and monitoring of the dynamic behavior of species directly involved in a reaction. The method, combined with proper in situ spectroscopy, is powerful for elucidating complex systems and noisy data as often encountered in heterogeneous catalytic reactions at solid–liquid and solid–gas interfaces under working conditions. The theoretical principle and actual data processing of MES are explained in detail. Periodic perturbation of the system by an external parameter, such as concentration and temperature, is utilized as stimulation in MES. The influence of stimulation shape upon response analysis is explained. Furthermore, an illustrative example of MES, enantioselective hydrogenation at a solid-liquid interface, is presented.

Liquid-crystalline dendrons carrying either a thiol or disulfide function which display nematic, smectic A, columnar, or chiral nematic phases have been synthesized. Their mesomorphic properties are in agreement with the nature of the mesogenic units and structure of the dendrons. The first-generation poly(aryl ester) dendron containing two cyanobiphenyl mesogenic units was used to functionalize gold nanoparticles. For full coverage, a smectic-like supramolecular organization on the nanometer scale is observed, when the gold nanoparticles are spread onto carbon-coated copper grids. This result indicates that the dendritic ligands reported here act as self-organization promoters.

The trigonal planar geometry of the nitrogen atom in commonly used phosphoramidite ligands is not in line with the traditional valence shell electron pair repulsion (VSEPR) model. In this work, the effects governing nitrogen configuration in several substituted aminophosphines, A₂PNB₂ (A or B = H, F, Cl, Br, Me, OMe, BINOP), are examined using modern computational analytic tools. The electron delocalization descriptions provided by both electron localization function (ELF) and block localized wavefunction analysis support the proposed relationships between conformation and negative hyperconjugative interactions. In the parent H₂PNH₂, the pyramidal nitrogen configuration results from nitrogen lone pair electron donation into the σ* P — H orbital. While enhanced effects are seen for F₂PNMe₂, placing highly electronegative fluorine substituents on nitrogen (i.e., Me₂PNF₂) eliminates delocalization of the nitrogen lone pair. Understanding and quantifying these effects can lead to greater flexibility in designing new catalysts.

The synthesis and characterization of new 1,10-phenanthroline-based chromophores LT1, LT2 and LD1 featuring fluorene unit(s) are reported. Their absorption and emission as well as their two-photon absorption properties in the 450–650 nm spectral range are discussed in comparison with the parent 1,10-phenanthroline and already described ligands L1 and L2.

(a) IXS spectrum recorded at (310) (solid diamonds) compared to the resolution function (solid line) . (b) Phonon dispersion in high-symmetry directions; experimental points empty symbols connected by a guide for the eyes (solid lines) are compared with the ab initio calculations (dashed lines) for the F43m structure. The estimated experimental errors are less than the symbol size.

Polarization-sensitive ultrafast infrared measurements on photoinduced electron transfer in donor-acceptor pairs in polar acetonitrile show distinct contributions from loose and tight ion pairs. Highly anisotropic signals from tight ion pairs reveal the importance of mutual orientation of the reactants (see picture) and thus the need to refine theoretical models based on spherical species that solely involve reaction distances.

Multiconfigurational quantum chemical calculations on the R-diimines dichromium compound confirm that the Cr−Cr bond, 1.80 Å, is among the shortest Cr^I−Cr^I bonds. However, the bond between the two Cr atoms is only a quadruple bond rather than a quintuple bond. The reason why the bond is so short has to be attributed to the strain in the NCCN ligand moieties.

A π-extended, redox-active bridging ligand 4′,5′-bis(propylthio)tetrathiafulvenyl[i]dipyrido[2,3-a:3′,2′-c]phenazine (L) was prepared via direct Schiff-base condensation of the corresponding diamine−tetrathiafulvalene (TTF) precursor with 4,7-phenanthroline-5,6-dione. Reactions of L with [Ru(bpy)₂Cl₂] afforded its stable mono- and dinuclear ruthenium(II) complexes 1 and 2. They have been fully characterized, and their photophysical and electrochemical properties are reported together with those of [Ru(bpy)₂(ppb)]²⁺ and [Ru(bpy)₂(μ-ppb)Ru(bpy)₂]⁴⁺ (ppb = dipyrido[2,3-a:3′,2′-c]phenazine) for comparison. In all cases, the first excited state corresponds to an intramolecular TTF → ppb charge-transfer state. Both ruthenium(II) complexes show two strong and well-separated metal-to-ligand charge-transfer (MLCT) absorption bands, whereas the ³MLCT luminescence is strongly quenched via electron transfer from the TTF subunit. Clearly, the transient absorption spectra illustrate the role of the TTF fragment as an electron donor, which induces a triplet intraligand charge-transfer state (³ILCT) with lifetimes of approximately 200 and 50 ns for mono- and dinuclear ruthenium(II) complexes, respectively.

The excited-state dynamics of covalently linked electron donor−acceptor systems consisting of N,N-dimethylaniline (DMA) as electron donor and either perylene (Pe) or cyanoperylene (CNPe) as acceptor has been investigated in a large variety of solvents, including a room-temperature ionic liquid, by using femtosecond time-resolved fluorescence and absorption spectroscopy. The negligibly small solvent dependence of the absorption spectrum of both compounds and the strong solvatochromism of the fluorescence are interpreted by a model where optical excitation results in the population of a locally excited state (LES) and emission takes place from a charge-separated state (CSS). This interpretation is supported by the fluorescence up-conversion and the transient absorption measurements that reveal substantial spectral dynamics in polar solvents only, occurring on time scales going from a few hundreds of femtoseconds in acetonitrile to several tens of picoseconds in the ionic liquid. The early transient absorption spectra are similar to those found in nonpolar solvents and are ascribed to the LES absorption. The late spectra due to CSS absorption show bands that are red-shifted relative to those of the radical anion of the acceptor moiety by an amount that depends on solvent polarity, pointing to partial charge separation. Global analysis of the time-resolved data indicates that the charge separation dynamics in PeDMA is essentially solvent controlled, whereas that in CNPeDMA is faster than diffusive solvation, this difference being accounted for by a larger driving force for charge separation in the latter. On the other hand, the CSS lifetime of PeDMA is of the order of a few nanoseconds independently of the solvent, whereas that of CNPeDMA decreases with increasing solvent polarity from a few nanoseconds to a few hundreds of picoseconds. Comparison of these results with previously published data on the fluorescence quenching of Pe and CNPe in pure DMA shows that the charge separation and the ensuing charge recombination occur on similar time scales independently of whether these processes are intra- or intermolecular.

The ground and excited states of neutral and cationic PuO and PuO₂ have been studied with multiconfigurational quantum chemical methods followed by second order perturbation theory, the CASSCF/CASPT2 method. Scalar relativistic effects and spin–orbit coupling have been included in the treatment. As literature values for the ionization energy of PuO₂ are in the wide range of ~6.6 eV to ~10.1 eV, a central goal of the computations was to resolve these discrepancies; the theoretical results indicate that the ionization energy is near the lower end of this range. The calculated ionization energies for PuO, PuO⁺ and PuO₂⁺ are in good agreement with the experimental values.

A strategy to construct approximants to the kinetic-energy-functional dependent component (v[ρ_A,ρ_B](→r)) of the effective potential in one-electron equations for orbitals embedded in a frozen-density environment [Eqs. (20) and (21) in Wesolowski and Warshel, J. Phys. Chem. 97, (1993) 8050 ] is proposed. In order to improve the local behavior of the orbital-free effective embedding potential near nuclei in the environment, the exact behavior of v_t[ρ_A,ρ_B](→r) at ρ_A→0 and ∫ρ_Bd→r = 2 is taken into account. As a result, the properties depending on the quality of this potential are invariably improved compared to the ones obtained using conventional approximants which violated the considered exact condition. The approximants obtained following the proposed strategy and especially the simplest one constructed in this work are nondecomposable, i.e., cannot be used to obtain the analytic expression for the functional of the total kinetic energy.

LiSc(BH₄)₄ has been prepared by ball milling of LiBH₄ and ScCl₃. Vibrational spectroscopy indicates the presence of discrete Sc(BH₄)₄⁻ ions. DFT calculations of this isolated complex ion confirm that it is a stable complex, and the calculated vibrational spectra agree well with the experimental ones. The four BH₄⁻ groups are oriented with a tilted plane of three hydrogen atoms directed to the central Sc ion, resulting in a global 8 + 4 coordination. The crystal structure obtained by high-resolution synchrotron powder diffraction reveals a tetragonal unit cell with a = 6.076 Å and c = 12.034 Å (space group P-42c). The local structure of the Sc(BH₄)₄⁻ complex is refined as a distorted form of the theoretical structure. The Li ions are found to be disordered along the z axis.

IR and Raman data were obtained from α-, β-, and mixed (β,γ)-Ca(BH ₄) ₂ samples and from the deuterated β,γ phase mixture. The results obtained with α phase indicate that the DFT calculated values for the B−H stretching modes and the lattice vibrations are fairly close to the experimental values. The spectral behavior at temperatures around the transition to the β phase shows a continuous transition and suggests the presence of disorder caused by reorientational motions of the [BH ₄] ⁻ ion in the β phase. The data indicate that there are more deformation bands observed for the mixed (β,γ) samples than for the α phase which indicates structural variations between the β and the γ phases.

The photophysical properties of multichromophoric systems consisting of eight red or blue naphthalene diimides (NDIs) covalently attached to a p-octiphenyl scaffold, as well as a blue bichromophoric system with a biphenyl scaffold, have been investigated in detail using femtosecond time-resolved spectroscopy. The blue octachromophoric systems have been recently shown to self-assemble as supramolecular tetramers in lipid bilayer membranes and to enable generation of a transmembrane proton gradient upon photoexcitation (Bhosale, S.; Sisson, A. L.; Talukdar, P.; Fürstenberg, A.; Banerji, N.; Vauthey, E.; Bollot, G.; Mareda, J.; Röger, C.; Würthner, F.; Sakai, N.; Matile, S. Science2006, 313, 84). A strong reduction of the fluorescence quantum yield was observed when going from the single NDI units to the multichromophoric systems in methanol, the effect being even stronger in a vesicular lipid membrane. Fluorescence up-conversion measurements reveal ultrafast self-quenching in the multichromophoric systems, whereas the formation of the NDI radical anion, evidenced by transient absorption measurements, points to the occurrence of photoinduced charge separation. The location of the positive charge could not be established unambiguously from the transient absorption measurements, but energetic considerations indicate that charge separation should occur between two NDI units in the blue systems, whereas both an NDI unit and the p-octiphenyl scaffold could act as electron donor in the red system. The lifetime of the charge-separated state was found to increase from 22 to 45 ps by going from the bi- to the octachromophoric blue systems in methanol, while a 400 ps decay component was observed in the lipid membrane. This lifetime lengthening is explained in terms of charge migration that is most efficient when the octachromophoric systems are assembled as supramolecular tetramers in the lipid membrane. Furthermore, the average charge-separated state lifetime of the red system in methanol is even larger and amounts to 750 ps. This effect cannot be simply explained in terms of Marcus inverted regime as the driving force for charge recombination in the red system is only slightly larger than in the blue one. A better spatial separation of the charges in the red system stemming from the localization of the hole on the p-octiphenyl scaffold could additionally contribute to the slowing down of charge recombination.

NaBH₄·2H₂O and NaBH₄ were studied by single-crystal X-ray diffraction and vibrational spectroscopy. In NaBH₄·2H₂O, the BH₄^- anion has a nearly ideal tetrahedral geometry and is bridged with two Na⁺ ions through the tetrahedral edges. The structure does not contain classical hydrogen bonds, but reveals strong dihydrogen bonds of 1.77-1.95 Å. Crystal structures and vibrational spectra of NaBr·2H₂O and NaBH₄·2H₂O reveal many similarities. The unit cell volume of NaBH₄·2H₂O increases linearly with temperature between 200 and 313 K. At 313-315 K, the hydrate decomposes into NaBH₄ and H₂O, which react to release hydrogen.

The excited-state dynamics of the methylperylene/tetracyanoethylene (MPe/TCNE) donor−acceptor complex has been investigated in various solvents using femtosecond transient absorption spectroscopy. The transient spectra reveal the formation of two types of ion pairs: The first (IP1), constituting the major fraction of the total ion-pair population, is characterized by a broad and red-shifted absorption spectrum compared to that of the free MPe cation and by a subpicosecond lifetime, whereas the second (IP2) has a spectrum closer to that of MPe cation and a lifetime of a few picoseconds. A substantial polarization anisotropy was observed with IP1 but not with IP2, indicating a relatively well-defined structure for the former. The reaction scheme that best accounts for the observed dynamics and its solvent dependence involves the simultaneous excitation of complexes that differ by their electronic coupling. The more coupled complexes have a high absorption coefficient and thus yield IP1, which undergoes ultrafast charge recombination, whereas the less coupled complexes have a lower probability to be excited and lead to the longer-lived IP2.

The mononuclear Os^II complex [Os( L1)₃](PF₆)₂ ( L1 = 5-methyl(1-methylbenzimidazol-2-yl)pyridine) is an obvious candidate for the design of an inert d-block-based tripodal receptor capable of binding and photosensitizing trivalent lanthanides (Ln^III). It has thus been prepared and its two enantiomeric meridional (Δ-mer and Λ-mer) and facial (rac-fac) isomers have been separated by ion-exchange chromatography. The optical isomers have been characterized by CD spectroscopy and assignments of absolute configuration confirmed by an X-ray crystallographic study of Λ-mer-[Os( L1)₃](PF₆)₂·1.5MeCN (monoclinic, P2₁, Z = 4). Comparison of the latter structure with that of racemic fac-[Os( L1)₃](PF₆)₂ (monoclinic, C2/c, Z = 8) and [Os(bipy)₃](PF₆)₂ (where bipy = 2,2' -bipyridine) shows minimal structural variations, but differences are observed in the photophysical and electrochemical properties of the respective compounds. Luminescence emissions from Os^II complexes of L1 are typically lower in energy, with shorter lifetimes and lower quantum yields than their bipy analogues, whilst metal-centred oxidation processes are more facile due to the enhanced π-donor ability of L1. The key relationships between these parameters are discussed. Finally, though challenged by (i) the low reactivity of many osmium precursors and (ii) the irreversible formation of competing side products, the synthesis and purification of the heterobimetallic triple-stranded helicate HHH-[OsLu( L2)₃](CF₃SO₃)₅ has been realised, in which L2 is a segmental ligand containing the same bidentate unit as that found in L1 further connected to a tridentate binding site adapted for complexing Ln^III. Its solid-state structure has been established by X-ray crystallography (triclinic, P1^-, Z = 2).

The La + O and La + O₂ chemiionization reactions have been investigated with quantum chemical methods. For La + O₂(X³Σ_g) and La + O₂(a¹Δ_g), the chemiionization reaction La + O₂ → LaO₂⁺ + e⁻ has been shown to be endothermic and does not contribute to the experimental chemielectron spectra. For the La + O₂(X³Σ_g) reaction conditions, chemielectrons are produced by La + O₂ → LaO + O, followed by La + O → LaO⁺ + e⁻. This is supported by the same chemielectron band, arising from La + O → LaO⁺ + e⁻, being observed from both the La + O(³P) and La + O₂(X³Σ_g) reaction conditions. For La + O₂(a¹Δ_g), a chemielectron band with higher electron kinetic energy than that obtained from La + O₂(X³Σ_g) is observed. This is attributed to production of O(¹D) from the reaction La + O₂(a¹Δ_g) → LaO + O(¹D), followed by chemiionization via the reaction La + O(¹D) → LaO⁺ + e⁻. Potential energy curves are computed for a number of states of LaO, LaO* and LaO⁺ to establish mechanisms for the observed La + O → LaO⁺ + e⁻ chemiionization reactions.

We report a comprehensive THz, infrared and optical study of Nb-doped SrTiO₃ as well as dc conductivity and Hall effect measurements. Our THz spectra at 7 K show the presence of an unusually narrow (<2  meV) Drude peak. For all carrier concentrations the Drude spectral weight shows a factor of three mass enhancement relative to the effective mass in the local density approximation, whereas the spectral weight contained in the incoherent midinfrared response indicates that the mass enhancement is at least a factor two. We find no evidence of a particularly large electron-phonon coupling that would result in small polaron formation.

We describe the preparation of a helicate containing four closely spaced, linearly arrayed copper(I) ions. This product may be prepared either directly by mixing copper(I) with a set of precursor amine and aldehyde subcomponents, or indirectly through the dimerization of a dicopper(I) helicate upon addition of 1,2-phenylenediamine. A notable feature of this helicate is that its length is not limited by the lengths of its precursor subcomponents: each of the two ligands wrapped around the four copper(I) centers contains one diamine, two dialdehyde, and two monoamine residues. This work thus paves the way for the preparation of longer oligo- and polymeric structures. DFT calculations and electrochemical measurements indicate a high degree of electronic delocalization among the metal ions forming the cores of the structures described herein, which may therefore be described as "molecular wires".

⁷⁷Se-enriched CpNi(bds) (bds = 1,2-benzenediselenolate), has been synthesized and its g tensor and ⁷⁷Se hyperfine tensors have been obtained from its frozen solution electron paramagnetic resonance (EPR) spectrum. These parameters are consistent with those calculated by density functional theory (DFT); it is shown that 10% of the spin is localized on each selenium and that the direction associated to the maximum ⁷⁷Se couplings is aligned along the g_min direction, perpendicular to the Ni(bds) plane. EPR measurements and DFT calculations are also carried out on the ⁷⁷Se enriched complex CpNi(dsit) as well on the two dithiolene analogues CpNi(bdt) and CpNi(dmit). The optimized structures of the isolated CpNi(bds) and CpNi(bdt) complexes have been used to generate the idealized dimers (bds)NiCp···CpNi(bds) and (bdt)NiCp···CpNi(bdt) characterized by Cp···Cp overlap. The exchange parameters J calculated at the DFT level for these systems are in reasonable accord with the experimental values. The influence of the geometry of the dimer on its magnetic properties is assessed by calculating the variation of J as a function of the relative orientation of the two Ni(diselenolene) or Ni(dithiolene) planes.

A large set of electronic states of scandium dimer has been calculated using high-level theoretical methods such as quantum diffusion Monte Carlo (DMC), complete active space perturbation theory as implemented in GAMESS-US, coupled-cluster singles, doubles, and triples, and density functional theory (DFT). The ³Σ_u and ⁵Σ_u states are calculated to be close in energy in all cases, but whereas DFT predicts the ⁵Σ_u state to be the ground state by 0.08 eV, DMC and CASPT2 calculations predict the ³Σ_u to be more stable by 0.17 and 0.16 eV, respectively. The experimental data available are in agreement with the calculated frequencies and dissociation energies of both states, and therefore we conclude that the correct ground state of scandium dimer is the ³Σ_u state, which breaks with the assumption of a ⁵Σ_u ground state for scandium dimer, believed throughout the past decades.

Excitation energy migration is an important phenomenon at high concentration of luminescent chromophores. In crystalline solids it results in a quenching of the intrinsic luminescence of the chromophore as the excitation energy migrates to impurity centres or other forms of trap sites. As concluded from the extensively studied systems where Cr³⁺ is doped as the active chromophore into inert host lattices, energy migration in crystalline solids is usually a phonon-assisted process, in which the simultaneous creation or annihilation of phonons helps to bridge the energy miss-match in the energy levels of two neighbouring chromophores within a inhomogeneously broadened absorption band. However, in the three-dimensional network systems [Ru(bpy)₃][NaCr(ox)₃] and [Rh(bpy)₃][NaCr(ox)₃]ClO₄, it proved possible to unambiguously identify three different mechanisms for energy migration within the R₁ line of the ⁴A₂ → ²E transition of Cr³⁺. In addition to the common temperature dependant phonon-assisted process, a resonant process between the zero-field split components of the ⁴A₂ ground state leading to a multi-line pattern in a fluorescence line narrowing spectrum and a quasi-resonant process within the same component leading to fast spectral diffusion can be identified at very low temperature. The parameters governing these processes are discussed and the behaviour of the model systems is compared to more conventional doped oxides and related systems.

The thermal and the light-induced spin transition in [Fe(bbtr)₃](ClO₄)₂ (bbtr = 1,4-di(1,2,3-triazol-1-yl)) as well as the high-spin → low-spin relaxation following the light-induced population of the high-spin state below the thermal transition temperature are discussed in relation to the accompanying crystallographic phase transition. The experimental data have exclusively been obtained using optical single crystal absorption spectroscopy.

The spin-crossover compound [Fe(bbtr)₃](ClO₄)₂ (bbtr = 1,4-di(1,2,3-triazol-1-yl)butane) forms a polymeric hexagonal sheet structure. It shows an abrupt thermal spin transition with 13 K wide hysteresis around 105 K, as evidenced by single crystal optical spectroscopy. The transition temperature for the thermal high-spin→low-spin transition on cooling as well as the relaxation kinetics just below T_c^↓ depend upon the history of the sample. This is typical for a nucleation and growth mechanism and domain formation. In contrast, the high-spin→low-spin relaxation following the light-induced population of the high-spin state at low temperatures is governed by the intersystem crossing process.

A series of mixed crystals with general formula Ba_7-xNa_yF₁₂Cl_2-zBr_z in the ordered modification (space group P-6) has been studied by single crystal x-ray diffraction. Depending on synthesis conditions, the disorder in the channels (i.e. occupation of 0 0 z sites) can be changed. The disorder is found to be correlated with the refined Na content, and its effect on Ba-Cl(Br) bond length is discussed.

Supramolecular 3D organization on gold with interdigitating intra- and interlayer recognition motifs (see picure, black p-oligophenyl rods; red, blue naphthalenediimide (NDI) stacks) is designed to access supramolecular cascade n/p-heterojunctions or the adaptable directionality needed to control fill factors in current-voltage curves.

The photophysics and excited-state dynamics of nitroperylene (NPe) in solvents of various polarities and viscosities, including a room-temperature ionic liquid, have been investigated by femtosecond-resolved transient absorption spectroscopy. The excited-state absorption spectrum was found to depend substantially on solvent polarity. In the most polar solvents, it is very similar to that of the NPe radical cation generated upon bimolecular quenching by an electron acceptor, denoting a substantial charge-transfer character of the S₁ state. Contrary to smaller nitroaromatic compounds, NPe in the S₁ state does not undergo ultrafast intersystem crossing (ISC) but decays mainly by internal conversion (IC). In nonprotic solvents, IC involves low-frequency modes with large amplitude motion associated with the nitro group and depends on both the solvent viscosity and polarity. It takes place on a 100 ps time scale in acetonitrile, while in cyclohexane, it is slow enough for ISC to become competitive. Moreover, both the fluorescence quantum yield and the excited-state dynamics were found to differ, depending on which side of the S₀−S₁ absorption band excitation was performed. This dependence is explained by the inhomogeneous nature of the absorption spectrum arising from a distribution of twist angles of the nitro group relative to the aromatic plane. On the other hand, such excitation wavelength effects were not observed in protic solvents, where the excited-state lifetime was found to be substantially shorter than that in nonprotic solvents. This behavior is rationalized in terms of a H-bonding interaction, which limits the torsional disorder of NPe and favors ultrafast nonradiative deactivation of the excited state. Transient absorption measurements performed for comparative purpose with nitropyrene in acetonitrile confirm the occurrence of ultrafast ISC in smaller nitroaromatic compounds.

A multireference second-order perturbation theory using a restricted active space self-consistent field wave function as reference (RASPT2/RASSCF) is described. This model is particularly effective for cases where a chemical system requires a balanced orbital active space that is too large to be addressed by the complete active space self-consistent field model with or without second-order perturbation theory (CASPT2 or CASSCF, respectively). Rather than permitting all possible electronic configurations of the electrons in the active space to appear in the reference wave function, certain orbitals are sequestered into two subspaces that permit a maximum number of occupations or holes, respectively, in any given configuration, thereby reducing the total number of possible configurations. Subsequent second-order perturbation theory captures additional dynamical correlation effects. Applications of the theory to the electronic structure of complexes involved in the activation of molecular oxygen by mono- and binuclear copper complexes are presented. In the mononuclear case, RASPT2 and CASPT2 provide very similar results. In the binuclear cases, however, only RASPT2 proves quantitatively useful, owing to the very large size of the necessary active space.

Some dimetal fullerenes M₂@C₆₀ (M = Cr, Mo, W) have been studied with computational quantum chemistry methods. The transition metal diatomic molecules Cr₂, Mo₂, W₂ form exohedral complexes with C₆₀, while U₂ forms a highly symmetric endohedral compound and it is placed in the center of the C₆₀ cavity. This highly symmetric structure is an artifact due to the small size of the C₆₀ cavity, which constrains U₂ at the center. If a larger cavity is used, like C₇₀ or C₈₄, U₂ preferentially binds the internal walls of the cavity and the U−U bond no longer exists.

Quantum mechanical calculations, using both CASPT2 and DFT methods, for the model systems (MeMMMe, PhMMPh, (MeMMMe)(C₆H₆)₂, Ar^§MMAr^§, Ar^#MMAr^#; M = Cr, Fe, Co; Ar^§ = C₆H₄-2(C₆H₅), Ar^# = C₆H₃-2,6(C₆H₃-2,6-Me₂)₂) are described. These studies were undertaken to provide a multireference description of the metal−metal bond in the simple dimers MeMMMe and PhMMPh (M = Cr, Fe, Co) and to determine the extent of secondary metal−arene interaction involving the flanking aryl rings of the terphenyl ligands in quintuply bonded Ar′CrCrAr′ (Ar′ = C₆H₃-2,6(C₆H₃-2,6-Prⁱ₂)₂). We show that in the Cr−Cr species the Cr−arene interaction is a feeble one that causes only a small weakening of the quintuple bond. In sharp contrast, in the analogous Fe and Co species strong η⁶-arene interactions that preclude significant metal−metal bonding are predicted.

The relative energies of side-on versus end-on binding of molecular oxygen to a supported Cu(I) species, and the singlet versus triplet nature of the ground electronic state, are sensitive to the nature of the supporting ligands and, in particular, depend upon their geometric arrangement relative to the O₂ binding site. Highly correlated ab initio and density functional theory electronic structure calculations demonstrate that optimal overlap (and oxidative charge transfer) occurs for the side-on geometry, and this is promoted by ligands that raise the energy, thereby enhancing resonance, of the filled Cu d_xz orbital that hybridizes with the in-plane π* orbital of O₂. Conversely, ligands that raise the energy of the filled Cu d_z² orbital foster a preference for end-on binding as this is the only mode that permits good overlap with the in-plane O₂ π*. Because the overlap of Cu d_z² with O₂ π* is reduced as compared to the overlap of Cu d_xz with the same O₂ orbital, the resonance is also reduced, leading to generally more stable triplet states relative to singlets in the end-on geometry as compared to the side-on geometry, where singlet ground states become more easily accessible once ligands are stronger donors. Biradical Cu(II)-O₂ superoxide character in the electronic structure of the supported complexes leads to significant challenges for accurate quantum chemical calculations that are best addressed by exploiting the spin-purified M06L local density functional, single-reference completely renormalized coupled-cluster theory, or multireference second-order perturbation theory, all of which provide predictions that are qualitatively and quantitatively consistent with one another.

The new bis(pentalene) complex Cr₂(η⁵:η⁵-C₈H₄^1,4-SiiPr₃)₂ has been synthesized and characterized; it is found to exhibit paramagnetism at room temperature, and solid-state magnetic studies show that the dimer is best modeled as containing a pair of antiferromagnetically interacting S = ½ centers with the separation between the singlet ground state and triplet excited state being 2.23 kJ mol⁻¹. Structural data show a Cr−Cr distance of 2.2514(15) Å, consistent with a strong metal−metal interaction. The bonding has been further investigated by density functional, hybrid, and CASPT2 methods. The metal−metal interaction is best described by a double bond with each metal having an 18-electron count. Theory predicts the singlet and triplet states to lie close in energy but puts the triplet state at a slightly lower energy than the singlet. The energy difference predicted by CASPT2 is closest to the experimental value.

A new type of stable radical ligand featuring a 1,1-bis-phosphinosulfide alkene backbone has been prepared and characterized on the basis of X-ray diffraction, EPR and DFT studies.

Laser-ablated Th atoms react with molecular hydrogen to give thorium hydrides and their dihydrogen complexes during condensation in excess neon and hydrogen for characterization by matrix infrared spectroscopy. The ThH₂, ThH₄, and ThH₄(H₂)_x (x = 1−4) product molecules have been identified through isotopic substitution (HD, D₂) and comparison to frequencies calculated by density functional theory and the coupled-cluster, singles, doubles (CCSD) method and those observed previously in solid argon. Theoretical calculations show that the Th−H bond in ThH₄ is the most polarized of group 4 and uranium metal tetrahydrides, and as a result, a strong attractive “dihydrogen” interaction was found between the oppositely charged hydride and H₂ ligands ThH₄(H₂)_x. This bridge-bonded dihydrogen complex structure is different from that recently computed for tungsten and uranium hydride super dihydrogen complexes but is similar to that recently called the “dihydrogen bond” (Crabtree, R. H. Science 1998, 282, 2000). Natural electron configurations show small charge flow from the Th center to the dihydrogen ligands.

The codeposition of laser-ablated tungsten atoms with neat hydrogen at 4 K forms a single major product with a broad 2500 cm^-1 and sharp 1860, 1830, 1782, 1008, 551, and 437 cm^-1 absorptions, which are assigned to the WH₄(H₂)₄ complex on the basis of isotopic shifts and agreement with isotopic frequencies calculated by density functional theory. This D_2d structured complex was computed earlier to form exothermically from W atoms and hydrogen molecules. Annealing the matrix allows hydrogen to evaporate and the complex to aggregate and ultimately to decompose. Comparison of the H−H stretching mode at 2500 cm^-1 and the W−H₂ stretching mode at 1782 cm^-1 with 2690 and 1570 cm^-1 values for the Kubas complex W(CO)₃(PR₃)₂(H₂) suggests that the present physically stable WH₄(H₂)₄ complex has more strongly bound dihydrogen ligands. Our CASPT2 calculations suggest a 15 kcal/mol average binding energy per dihydrogen molecule in the WH₄(H₂)₄ complex.

Gradient-dependent approximations to the functional of the kinetic energy of non-interacting electrons (T_s[ρ]), which reflect various properties of the exact functional, are considered. For specially constructed pairs of electron densities, for which the analytic expression for the differences of T_s[ρ] is known, it is shown that the accuracy of the quantities derivable from a given approximation to T_s[ρ]: energy differences and their functional derivatives, does not reflect that of T_s[ρ] itself. The comparisons between the exact values of the kinetic energy in such cases are proposed as an independent condition/criterion for appraisal of approximations to T_s[ρ].

Two new ethynylbipyridine-linked mono- and bis-tetrathiafulvalene (TTF) derivatives, together with a Ru(II) complex, were synthesized using Sonogashira coupling reactions and characterized by UV/vis spectroscopy and cyclic voltammetry. They display a clear electrochemically amphoteric behavior consisting of two reversible single-electron oxidation waves (typical for TTF derivatives) and one reversible single-electron reduction wave (bpy) and act as donor–acceptor (D–A) systems. Furthermore, for the Ru(II) complex, a quite intense fluorescence originating from the ³MLCT state is observed.

The luminescence of Sm²⁺ substituting for Sr²⁺ or Ba²⁺ has been studied in SrFBr, BaFBr, BaFI and SrAlF₅.

The pressure induced shifts of the intra-configurational ⁵D_0,1 → ⁷F_0,1,2 observed in the MFX crystals are about three times larger than those observed in ruby, confirming thus some potential of these systems as pressure sensors.

The comparison of excitation spectra in MFX shows that the position of the lowest 4f⁵5d¹ band shifts strongly to the red passing from SrFBr to BaFI. In BaFI, one observes simultaneously intra-configurational and inter-configurational emission.

The non-degenerate ⁵D₀ → ⁷F₀ emission of Sm²⁺ in SrAlF₅ confirms the presence of four crystallographic sites for Sr. Site selective spectra show clear differences for the different sites. Spectra as a function of pressure reveal different pressure shifts for the different sites.

The charge recombination dynamics of excited donor−acceptor complexes consisting of hexamethylbenzene (HMB), pentamethylbenzene (PMB), and isodurene (IDU) as electron donors and tetracyanoethylene (TCNE) as electron acceptor in various polar solvents has been investigated within the framework of the stochastic approach. The model accounts for the reorganization of intramolecular high-frequency vibrational modes as well as for the solvent reorganization. All electron-transfer energetic parameters have been determined from the resonance Raman data and from the analysis of the stationary charge transfer absorption band, while the electronic coupling has been obtained from the fit to the charge recombination dynamics in one solvent. It appears that nearly 100% of the initially excited donor−acceptor complexes recombine in a nonthermal (hot) stage when the nonequilibrium wave packet passes through a number of term crossings corresponding to transitions toward vibrational excited states of the electronic ground state. Once all parameters of the model have been obtained, the influence of the dynamic solvent properties (solvent effect) and of the carrier frequency of the excitation pulse (spectral effect) on the charge recombination dynamics have been explored. The main conclusions are (i) the model provides a globally satisfactory description for the IDU/TCNE complex although it noticeably overestimates the spectral effect, (ii) the solvent effect is quantitatively well described for the PMB/TCNE and HMB/TCNE complexes but the model fails to reproduce their spectral effects, and (iii) the positive spectral effect observed with the HMB/TCNE complex cannot be described within the framework of two-level models and the charge redistribution in the excited complexes should most probably be taken into account.

Variational methods to treat a many-electron system embedded in the environment, which is represented by means of only its electron density, are considered. It is shown that the embedding operator is a local potential in the case where the electron-electron repulsion is treated exactly and the trial embedded wave function takes the multideterminantal form with a fixed number of determinants. The local embedding potential is constructed by imposing that it leads to the same electron density as the one which minimizes the Hohenberg-Kohn functional. For the limiting cases of single-determinant and configuration interaction forms of the embedded wave function, the expressions for the local embedding potential using commonly known density functionals are given. The relation between the derived local embedding potential and the effective embedding potential in the case of the embedded Kohn-Sham system [T. A. Wesołowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993)] is discussed in detail.

SrMgF₄ was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF₄ was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis.

Americium and curium oxides AmO_n and CmO_n (n = 1, 2) were studied using state-of-the-art multiconfigurational, relativistic, quantum chemical methods. Spectroscopic properties for the ground state and several excited states of the four target compounds were determined. The computed dissociation energy of AmO (4.6 eV) agrees fairly well with estimates derived from experimental studies (5.73 ± 0.37 eV) while the computed dissociation energy of CmO (7.1 eV) agrees well with the experimental value (7.5 eV). The computed ionization energy of AmO (6.3 eV) is in good agreement with the current experimental value (5.9 ± 0.2 eV).

Values of σ and σ⁺, for use in linear free energy relationships, are determined for para hydrogen atoms having nuclear charges other than 1 (nucleomers). Hammett ρ values for a variety of free energies of activation, reaction, and other extrathermodynamic properties (e.g., vibrational frequencies) are computed therefrom and compared to those computed using typical para functional groups. The nucleomer correlations show excellent qualitative agreement with standard correlations but the quantitative agreement is less good, typically underestimating the standard ρ-value by 10-60%.

Biological homochirality on earth and its tremendous consequences for pharmaceutical science and technology has led to an ever increasing interest in the selective production, the resolution and the detection of enantiomers of a chiral compound. Chiral surfaces and interfaces that can distinguish between enantiomers play a key role in this respect as enantioselective catalysts as well as for separation purposes. Despite the impressive progress in these areas in the last decade, molecular-level understanding of the interactions that are at the origin of enantiodiscrimination are lagging behind due to the lack of powerful experimental techniques to spot these interactions selectively with high sensitivity. In this article, techniques based on infrared spectroscopy are highlighted that are able to selectively target the chiral properties of interfaces. In particular, these methods are the combination of Attenuated Total Reflection InfraRed (ATR-IR) with Modulation Excitation Spectroscopy (MES) to probe enantiodiscriminating interactions at chiral solid–liquid interfaces and Vibrational Circular Dichroism (VCD), which is used to probe the structure of chirally-modified metal nanoparticles. The former technique aims at suppressing signals arising from non-selective interactions, which may completely hide the signals of interest due to enantiodiscriminating interactions. Recently, this method was successfully applied to investigate enantiodiscrimination at self-assembled monolayers of chiral thiols on gold surfaces. The nanometer size analogues of the latter—gold nanoparticles protected by a monolayer of a chiral thiol—are amenable to VCD spectroscopy. It is shown that this technique yields detailed structural information on the adsorption mode and the conformation of the adsorbed thiol. This may also turn out to be useful to clarify how chirality can be bestowed onto the metal core itself and the nature of the chirality of the latter, which is manifested in the metal-based circular dichroism activity of these nanoparticles.

Attenuated total reflection infrared (ATR-IR) spectroscopy in a flow-through cell was used to study the photocatalytic mineralization of malonic acid and succinic acid over P25 TiO₂ in situ. The experiments were performed in water at concentrations of 1.5×10⁻⁴ mol/L and pH 3.5 at room temperature. Changes on the catalyst surface were observed within a few minutes. The first step in the mineralization of malonic acid is a photo-Kolbe reaction of adsorbed malonate. Part of the resulting C₂ species is converted into oxalate and finally into carbon dioxide, and part desorbs from the surface. The branching ratio for the two pathways is 50:50. The mineralization reaction was also observed in the absence of dissolved oxygen, but at a slower rate. In the presence of dissolved ¹⁸O₂, labeled oxygen was incorporated into the adsorbed oxalate. A dominant pathway in the mineralization of succinic acid involves the transformation to oxalate via malonate. Thus, it is proposed that a favored pathway for dicarboxylic acid mineralization is a photo-Kolbe reaction, followed by oxidation of the carbon-centered radical to a carboxylate, which corresponds to the overall formal shortening of the alkyl chain by one CH₂ unit.

We introduce zipper assembly as a simple and general concept to create complex functional architectures on conducting surfaces. Rigid-rod π-stack architecture composed of p-oligophenyl rods and blue naphthalenediimide (NDI) stacks is selected as an example. First, short p-quaterphenyl initiators with four anionic NDIs are deposited on gold. Then, long p-octiphenyl propagators with eight cationic NDIs are added. The lower half of the propagator π-stacks with the initiator, whereas the upper half of the molecule remains free. These cationic sticky-ends zip up with anionic propagators to produce anionic sticky-ends, and so on. Zipper assembly on gold nanoparticles is demonstrated by the appearance of the absorption of face-to-face NDI π-stacks and the shift of the surface plasmon resonance band with increasing layer thickness. Complete inhibition by zipper capping demonstrates that zipper assembly affords complex architectures that are more ordered than those obtained by conventional layer-by-layer (LBL) approaches. Zipper assembly on gold electrodes produces increasing photocurrents with increasing number of zipped layers. The photocurrents obtained by this method are much higher than those obtained by conventional LBL controls; zipper termination by capping cleanly stops any increase in photocurrent.

Bis-iminophosphoranes containing various types of linkers between two R₃P=N moieties were electrochemically oxidized at controlled potential in situ in the electron spin resonance (ESR) cavity. For linkers constituted of phenylenes, conjugated phenylenes or merely a dicyanoethylenic bond, this oxidation led to well-resolved ESR spectra which were characterized by their g values and by their ¹H, ¹⁴N and ³¹P isotropic hyperfine constants. These coupling constants agree with those calculated by DFT for the corresponding cation radicals. Experimental and theoretical results clearly indicate that in these species the unpaired electron is mostly delocalized on the bridge and on the nitrogen atoms while the spin density on the phosphorus atoms is particularly small. Cyclic voltammetry and ESR spectra show that the nature of the bridge between the two iminophosphoranes considerably influences the oxidation potential of the compound as well as the stability of the radical cation. Information about the conformation of the precursor containing two Ph₃P=N moieties separated by a —C(CN)=C(CN)—group was obtained from its crystal structure.

Macrophage infectivity potentiator (MIP) was originally reported to be a chlamydial lipoprotein from experiments showing incorporation of radiolabeled palmitic acid into native and recombinant MIP; inhibition of posttranslational processing of recombinant MIP by globomycin, known to inhibit signal peptidase II; and solubility of native MIP in Triton X-114. However, the detailed structural characterization of the lipid moiety on MIP has never been fully elucidated. In this study, bioinformatics and mass spectrometry analysis, as well as radiolabeling and immunochemical experiments, were conducted to further characterize MIP structure and subcellular localization. In silico analysis showed that the amino acid sequence of MIP is conserved across chlamydial species. A potential signal sequence with a contained lipobox was identified, and a recombinant C20A variant was prepared by replacing the probable lipobox cysteine with an alanine. Both incorporation of U-¹⁴C-esterified glycerol and [U-¹⁴C]palmitic acid and posttranslational processing that was inhibitable by globomycin were observed for recombinant wild-type MIP but not for the recombinant C20A MIP variant. The fatty acid contents of native and recombinant MIP were analyzed by gas chromatography-mass spectrometry, and the presence of amide-linked fatty acids in recombinant MIP was investigated by alkaline methanolysis. These results demonstrated a lipid modification in MIP similar to that of other prokaryotic lipoproteins. In addition, MIP was detected in an outer membrane preparation of Chlamydia trachomatis elementary bodies and was shown to be present at the surfaces of elementary bodies by surface biotinylation and surface immunoprecipitation experiments.

A new barium silico-aluminate phase with the stoichiometry Ba13.35(1) Al30.7 Si5.3 O70 has been found and characterized. The compound crystallizes in the space group P63 /m (No. 176) with a = 15.1683(17) Å, c = 8.8708(6) Å, V = 1767.5(4) ų , Z = 1, Rw = 0.026, 32 refined parameters. A 3-dimensional matrix of Al/SiO4 tetrahedra with Ba(II) ions located in channels along the c axis builds up the structure. One of these channels is partially filled with Ba(II) ions (CN 6+3) in Wyckoff position 2a, leaving ∼ 1/3 of the positions empty. The second and third type of Ba(II) ions occupy channels orientated along the c axis with CN 4+2+2 and 4+3+1, respectively. The structure shows a rare clustered arrangement of six tetrahedra filled exclusively by Al(III) and therefore is an exception to Loewenstein’s rule. The other tetrahedral positions show an Al to Si ratio of ∼ 4 : 1. The Al/Si–O bond lengths in the tetrahedral Al/Si positions drawn vs. site occupation show linear behavior similar to the prediction by Vegard’s rule for solid solutions. After doping with Eu(II) the compound shows bright orange-yellow luminescence with an unusual large shift of the Eu(II) emission band.

The creation of long-lived charge-separated states in donor-acceptor assemblies has been the goal of many studies aimed at mimicking the primary processes in photosynthesis. Here we present such assemblies based on tetrathiafulvalene (TTF) as electron donor and a dipyridophenazine (dppz) unit as electron acceptor in the form of a fused ligand (TTF-dppz) coordinated to ruthenium(II) via the dipyrido coordination site and with 2,2′-bipyridine (bpy) as auxiliary ligand, namely [Ru(bpy)_3−x(TTF-dppz)_x]²⁺ (x = 1−3). For x = 2, irradiation into the metal to dppz charge transfer transition results in electron transfer from TTF to ruthenium, thus creating a charge-separated state best described by [(TTF⁺-dppz)Ru(dppz⁻-TTF)(bpy)]²⁺ with a lifetime of 2.5 μs in dichloromethane.

We discuss and illustrate by several examples how the ultrafast excited-state dynamics of a chromophore can be altered when changing its environment from a homogenous solution to a biological molecule such as proteins or nucleic acids.

A series of copper(I)−α-ketocarboxylate complexes have been prepared and shown to exhibit variable coordination modes of the α-ketocarboxylate ligand. Reaction with O₂ induces decarboxylation of this ligand, and the derived copper−oxygen intermediate(s) has been intercepted, resulting in hydroxylation of an arene substituent on the supporting N-donor ligand. Theoretical calculations have provided intriguing mechanistic notions for the process, notably implicating hydroxylation pathways that involve novel [Cu^I−OOC(O)R] and [Cu^II−O^-• ↔ Cu^III = O^2-]⁺ species.

Molecular dynamics simulations of Cm(III) in water were performed at two different temperatures, namely, T = 300 K and T = 473 K. Fully ab initio intermolecular potentials were employed. At the lower temperature, T = 300 K, nine water molecules coordinate preferentially the Cm(III) ion in the first coordination sphere, while at the higher temperature, T = 473 K, the preferential coordination number is eight instead of nine. The number of water molecules in the second coordination sphere is not uniquely defined, but the most probable number is 16.

The excited-state dynamics of the DNA intercalator YO-PRO-1 and of three derivatives has been investigated in water and in DNA using ultrafast fluorescence spectroscopy. In the free form, the singly charged dyes exist both as monomers and as H-dimers, while the doubly charged dyes exist predominantly as monomers. Both forms are very weakly fluorescent: the monomers because of ultrafast nonradiative deactivation, with a time constant on the order of 3−4 ps, associated with large amplitude motion around the methine bridge, and the H-dimers because of excitonic interaction. Upon intercalation into DNA, large amplitude motion is inhibited, H-dimers are disrupted, and the molecules become highly fluorescent. The early fluorescence dynamics of these dyes in DNA exhibits substantial differences compared with that measured with their homodimeric YOYO analogues, which are ascribed to dissimilarities in their local environment. Finally, the decay of the fluorescence polarization anisotropy reveals ultrafast hopping of the excitation energy between the intercalated dyes. In one case, a marked change of the depolarization dynamics upon increasing the dye concentration is observed and explained in terms of a different binding mode.

The topology of the ground-state potential energy surface of M(CN)₆ with orbitally degenerate ²T_2g (M = Ti^III (t_2g¹), Fe^III and Mn^II (both low-spin t_2g⁵)) and ³T_1g ground states (M = V^III (t_2g²), Mn^III and Cr^II (both low-spin t_2g⁴)) has been studied with linear and quadratic Jahn−Teller coupling models in the five-dimensional space of the ε_g and τ_2g octahedral vibrations (T_g⊗(ε_g+τ_2g) Jahn−Teller coupling problem (T_g = ²T_2g, ³T_1g)). A procedure is proposed to give access to all vibronic coupling parameters from geometry optimization with density functional theory (DFT) and the energies of a restricted number of Slater determinants, derived from electron replacements within the t_2g^1,5 or t_2g^2,4 ground-state electronic configurations. The results show that coupling to the τ_2g bending mode is dominant and leads to a stabilization of D_3d structures (absolute minima on the ground-state potential energy surface) for all complexes considered, except for [Ti(CN)₆]^3-, where the minimum is of D_4h symmetry. The Jahn−Teller stabilization energies for the D_3d minima are found to increase in the order of increasing CN−M π back-donation (Ti^III < V^III < Mn^III < Fe^III < Mn^II < Cr^II). With the angular overlap model and bonding parameters derived from angular distortions, which correspond to the stable D_3d minima, the effect of configuration interaction and spin−orbit coupling on the ground-state potential energy surface is explored. This approach is used to correlate Jahn−Teller distortion parameters with structures from X-ray diffraction data. Jahn−Teller coupling to trigonal modes is also used to reinterpret the anisotropy of magnetic susceptibilities and g tensors of [Fe(CN)₆]^3-, and the ³T_1g ground-state splitting of [Mn(CN)₆]^3-, deduced from near-IR spectra. The implications of the pseudo Jahn−Teller coupling due to t_2g−e_g orbital mixing via the trigonal modes (τ_2g) and the effect of the dynamic Jahn−Teller coupling on the magnetic susceptibilities and g tensors of [Fe(CN)₆]^3- are also addressed.

The spin transition of the [Co(terpy)₂]²⁺ complex (terpy = 2,2′:6′,2″-terpyridine) is analysed based on experimental data from optical spectroscopy and magnetic susceptibility measurements. The single crystal absorption spectrum of [Co(terpy)₂](ClO₄)₂ shows an asymmetric absorption band at 14 400 cm⁻¹ with an intensity typical for a spin-allowed d–d transition and a temperature behaviour typical for a thermal spin transition. The single crystal absorption spectra of suggest that in this compound, the complex is essentially in the high-spin state at all temperatures. However, the increase in intensity observed in the region of the low-spin MLCT transition with increasing temperature implies an unusual partial thermal population of the low-spin state of up to about 10% at room temperature. Finally, high-spin → low-spin relaxation curves following pulsed laser excitation for [Co(terpy)₂](ClO₄)₂ dispersed in KBr discs, and as a comparison for the closely related [Co(4-terpyridone)₂](ClO₄)₂ spin-crossover compound are given.

An unsymmetric, peripherally octasubstituted phthalocyanine (Pc) 1, which contains a combination of dipyrido[3,2-f:2‘,3‘-h] quinoxaline and 3,5-di-tert-butylphenoxy substituents, has been obtained via a statistical condensation reaction of two corresponding phthalonitriles. Synthetic procedures for the selective metalation of the macrocyclic cavity and the periphery of 1 were developed, leading to the preparation of the key precursor metallophthalocyanines 3−5 in good yields. Two different strategies were applied to the synthesis of compact dyads MPc−Ru(II) 6−8 (M = Mg(II), Co(II), Zn(II)). Intramolecular electronic interactions in these dyads were studied by absorption, emission, and transient absorption spectroscopy. Upon photoexcitation, these dyads exhibit efficient intramolecular energy transfer from the Ru(II) chromophore to the MPc moiety.

The vibrational spectra of UBz and ThBz have been measured in solid argon. Complementary quantum chemical calculations have allowed the assignments of the vibrational spectra. According to the calculations, AcBz are stable molecules, as well as other species like BzAcBz and BzAc₂Bz. Experimentally, there is no evidence for the sandwich compounds BzAcBz and BzAc₂Bz due to the limitations in the reagent concentrations.

Capacitively coupled contactless conductivity detection (C⁴D) is a new technique providing high sensitivity in capillary electrophoresis (CE) especially for small ions that can otherwise only be determined with indirect methods. In this work, direct determination and validation of valproic acid (VPA) in biological fluids was achieved using CE with C⁴D. VPA is of pharmacological interest because of its use in epilepsy and bipolar disorder. The running electrolyte solution used consisted of 10 mM 2-(N-morpholino)ethane sulfonic acid (MES)/dl-histidine (His) and 50 μM hexadecyltrimethylammonium bromide (HTAB) at pH 6.0. Caproic acid (CA) was selected as internal standard (IS). Analyses of VPA in serum, plasma and urine samples were performed in less than 3 min. The interference of the sample matrix was reduced by deproteinization of the sample with acetonitrile (ACN). The effect of the solvent type and ratio on interference was investigated. The limits of detection (LOD) and quantitation (LOQ) of VPA in plasma samples were determined as 24 and 80 ng/ml, respectively. The method is linear between the 2 and 150 μg/ml, covering well the therapeutic range of VPA (50–100 μg/ml).

Rearrangement of cholesta-2,4,6-triene in the presence of p-toluenesulfonic acid in acetic acid at 70 °C leads to 4-methyl-19-nor-cholesta-1,3,5(10)-triene and 1(10 → 6)-abeo-14β-cholesta-5,7,9(10)-triene in less than 2 h. Postulated mechanisms of formation of these products are supported by molecular mechanics calculations of the relative stabilities of reaction intermediates. The results suggest that Δ^5,7-sterols, the most common natural precursors of triunsaturated steroidal hydrocarbons in contemporary sediments, constitute another major source for monoaromatic A and B steroids in addition to Δ⁵-sterols.

Interaction energies for a representative sample of 39 intermolecular complexes are calculated using two computational approaches based on the subsystem formulation of density functional theory introduced by Cortona (Phys. Rev. B 44:8454, 1991), adopted for studies of intermolecular complexes (Wesolowski and Weber in Chem. Phys. Lett. 248:71, 1996). The energy components (exchange-correlation and non-additive kinetic) expressed as explicit density functionals are approximated by means of gradient-free- (local density approximation) of gradient-dependent- (generalized gradient approximation) approximations. The sample of the considered intermolecular complexes was used previously by Zhao and Truhlar to compare the interaction energies derived using various methods based on the Kohn-Sham equations with high-level quantum chemistry results considered as the reference. It stretches from rare gas dimers up to strong hydrogen bonds. Our results indicate that the subsystem-based methods provide an interesting alternative to that based on the Kohn-Sham equations. Local density approximation, which is the simplest approximation for the relevant density functionals and which does not rely on any empirical data, leads to a computational approach comparing favorably with more than twenty methods based on the Kohn-Sham equations including the ones, which use extensively empirical parameterizations. For various types of non-bonding interactions, the strengths and weaknesses of gradient-free and gradient-dependent approximations to exchange-correlation and non-additive kinetic energy density functionals are discussed in detail.

The influence of pressure on the structural and vibrational properties of a₂RuH₆has been investigated using periodic density functional theory calculations performed at the local density approximation (LDA) and generalized gradient approximation (GGA) levels. At ambient pressure, the calculated structure and vibrational frequencies are in satisfactory agreement with experimental data. The calculated em>P-Vcurves could be fitted with the Vinet equation of state, yielding em>B₀=67.6and em>B₀=58.5  GPaat the LDA and GGA levels, respectively, and em>B₀^′=4.0at both theoretical levels. The unit cell parameter is found to decrease faster with increasing pressure than the Ru–H bond length. The calculated pressure dependence of the vibrational frequencies agrees well with experiment for em>ν₅(T_2g)but not for em>ν₉(A_1g)

Unexpected structural complexity: Well-crystallized Mg(BH₄)₂ powder is obtained, allowing the structure to be determined from synchrotron X-ray and neutron diffraction data. Mg(BH₄)₂ is a novel and remarkably complex three-dimensional framework in which each Mg²⁺ ion (blue) is tetrahedrally coordinated by four [BH₄]^- tetrahedra (B red, H gray; see picture).

Three ruthenium(II) polypyridine complexes of general formula [Ru(bpy)_3-n(TTF-dppz)_n](PF₆)₂ (n=1-3, bpy=2,2'-bipyridine), with one, two or three redox-active TTF-dppz (4',5'-bis(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2',3'-c]phenazine) ligands, were synthesised and fully characterised. Their electrochemical and photophysical properties are reported together with those of the reference compounds [Ru(bpy)₃](PF₆)₂, [Ru(dppz)₃](PF₆)₂ and [Ru(bpy)₂(dppz)](PF₆)₂ and the free TTF-dppz ligand. All three complexes show intraligand charge-transfer (ILCT) fluorescence of the TTF-dppz ligand. Remarkably, the complex with n=1 exhibits luminescence from the Ru²⁺dppz metal-to-ligand charge-transfer (³MLCT) state, whereas for the other two complexes, a radiationless pathway via electron transfer from a second TTF-dppz ligand quenches the ³MLCT luminescence. The TTF fragments as electron donors thus induce a ligand-to-ligand charge-separated (LLCS) state of the form TTF-dppz^--Ru²⁺→ -dppz-TTF⁺. The lifetime of this LLCS state is approximately 2.3 μs, which is four orders of magnitude longer than that of 0.4 ns for the ILCT state, because recombination of charges on two different ligands is substantially slower.

The excited-state dynamics of oligomeric phenyleneethynylenes (OPEs) of various length and substitution has been investigated by femtosecond time-resolved spectroscopy. The fluorescence lifetime of the OPEs decreases with the number of phenyleneethynylene units up to about 9. This effect is due to an increase of the oscillator strength for the S₁–S₀ transition. Dynamic features occurring within a few tens of picoseconds and ascribed to structural relaxation directly after population of the S₁ state can be observed in non-viscous solvents. The effect of torsional disorder on the fluorescence intensity is shown to depend strongly on the nature of the substituent on the phenyl groups. All these effects are qualitatively discussed with a simple exciton model.

Design, synthesis and evaluation of advanced rigid-rod π-stack photosystems with asymmetric scaffolds are reported. The influence of push–pull rods on self-organization, photoinduced charge separation and photosynthetic activity is investigated and turns out to be surprisingly small overall.

The fluorescence enhancement mechanisms of a series of DNA stains of the oxazole yellow (YO) family have been investigated in detail using steady-state and ultrafast time-resolved fluorescence spectroscopy. The strong increase in the fluorescence quantum yield of these dyes upon DNA binding is shown to originate from the inhibition of two distinct processes: 1) isomerisation through large-amplitude motion that non-radiatively deactivates the excited state within a few picoseconds and 2) formation of weakly emitting H-dimers. As the H-dimers are not totally non-fluorescent, their formation is less efficient than isomerisation as a fluorescent contrast mechanism. The propensity of the dyes to form H-dimers and thus to reduce their fluorescence contrast upon DNA binding is shown to depend on several of their structural parameters, such as their monomeric (YO) or homodimeric (YOYO) nature, their substitution and their electric charge. Moreover, these parameters also have a substantial influence on the affinity of the dyes for DNA and on the ensuing sensitivity for DNA detection. The results give new insight into the development and optimisation of fluorescent DNA probes with the highest contrast.

The influence of solute−solvent interactions on the vibrational energy relaxation dynamics of perylene and substituted perylenes in the first singlet excited-state upon excitation with moderate (<0.4 eV) excess energy has been investigated by monitoring the early narrowing of their fluorescence spectrum. This narrowing was found to occur on timescales ranging from a few hundreds of femtoseconds to a few picoseconds. Other processes, such as a partial decay of the fluorescence anisotropy and the damping of a low-frequency oscillation due to the propagation of a vibrational wavepacket, were found to take place on a very similar time scale. No significant relationship between the strength of nonspecific solute−solvent interactions and the vibrational energy relaxation dynamics of the solutes could be evidenced. On the other hand, in alcohols the spectral narrowing is faster with a solute having H-bonding sites, indicating that this specific interaction tends to favor vibrational energy relaxation. No relationship between the dynamics of spectral narrowing and macroscopic solvent properties, such as the thermal diffusivity, could be found. On the other hand, a correlation between this narrowing dynamics and the number of low-frequency modes of the solvent molecules was evidenced. All these observations cannot be discussed with a model where vibrational energy relaxation occurs via two consecutive and dynamically well-separated steps, namely ultrafast intramolecular vibrational redistribution followed by slower vibrational cooling. On the contrary, the results indicate that both intra- and intermolecular vibrational energy redistribution processes are closely entangled and occur, at least partially, on similar timescales.

The synthesis and characterization of two ortho-dimethyltetrathiafulvalene (o-DMTTF)-based rigid dimers containing dimethylsilicon (Me₂Si) or dimethylgermanium (Me₂Ge) linkers are described. Single-crystal X-ray analysis reveals planar geometry for the central 1,4-disilicon or 1,4-digermanium six-membered rings. DFT calculations provide optimized conformations in agreement with the experimental ones, and also emphasize the role of the heteroatomic linkers in the conjugation between the two redox active units. Cyclic voltammetry measurements show sequential oxidation into radical cation, and then dication species. Solution EPR measurements on the radical-cation species indicate full delocalization of the unpaired electron over both electroactive TTF units, with an associated coupling of 0.42 G with twelve equivalent protons. DFT calculations afford fully planar geometry for the radical-cation species and confirm the experimental isotropic coupling constant. Single-crystal X-ray analyses of two charge-transfer compounds obtained upon chemical oxidation, formulated as [(Me₂Si)₂(o-DMTTF)₂]-1/2[TCNQ]·1/2[TCNQF₄] and [(Me₂Ge)₂(o-DMTTF)₂]·[TCNQ], demonstrate the occurrence of genuine mixed-valence radical-cation species, as well as a three-dimensional network of short S···S intermolecular contacts. Temperature-dependent conductivity measurements demonstrate semiconducting behavior for both charge-transfer compounds, with an increase of the absolute value of the conductivity upon applying external pressure. Band structure calculations reveal peculiar pseudo-two-dimensional electronic structures, also confirming electronic interactions through SiMe₂ and GeMe₂ bridges.

The emergence of a family of computational methods, known under the label ‘density functional theory∈dex theory! density functional ’ or ‘DFT’, revolutionalized the field of computer modelling of complex molecular systems. Many computational schemes belonging to the DFT family are currently in use. Some of them are designed to be universal (nonempirical) whereas other to treat specific systems and/or properties (empirical). This review starts with the introduction of the formal elements underlying all these methods: Hohenberg-Kohn theorems∈dex theorem! Hohenberg-Kohn , reference system∈dex reference system of noninteracting electrons∈dex reference system! noninteracting electrons , exchange-correlation energy∈dex energy functional! exchange-correlation functional∈dex functional , and the Kohn-Sham equations∈dex equation! Kohn-Sham . The main roads to approximate the exchange-correlation-energy functional based on: local density approximation∈dex approximation! local density (LDA), generalized gradient approximation∈dex approximation! generalized gradient (GGA), meta-GGA∈dex energy functional! exchange-correlation! meta-GGA , and adiabatic connection∈dex adiabatic connection formula (hybrid functionals∈dex energy functional! exchange-correlation! hybrid ), are outlined. The performance of these approximations in describing molecular properties of relevance to intermolecular interaction∈dex interactions! intermolecular s and their interactions with environment in condensed phase (ionization potential∈dex potential! ionization s, electron∈dex electron affinities∈dex electron! affinity , electric moments∈dex electric moment , polarizabilities∈dex polarizability ) is reviewed. Developments concerning new methods situated within the general Hohenberg-Kohn-Sham framework or closely related to it are overviewed in the last section

The subsystem formulation of density functional theory is used to obtain equilibrium geometries and interaction energies for a representative set of noncovalently bound intermolecular complexes. The results are compared with literature benchmark data. The range of applicability of two considered approximations to the exchange-correlation- and nonadditive kinetic energy components of the total energy is determined. Local density approximation, which does not involve any empirical parameters, leads to excellent intermolecular equilibrium distances for hydrogen-bonded complexes (maximal error 0.13 Å for NH₃−NH₃). It is a method of choice for a wide class of weak intermolecular complexes including also dipole-bound and the ones formed by rare gas atoms or saturated hydrocarbons. The range of applicability of the chosen generalized gradient approximation, which was shown in our previous works to lead to good interaction energies in such complexes, where π-electrons are involved in the interaction, remains limited to this group because it improves neither binding energies nor equilibrium geometries in the wide class of complexes for which local density approximation is adequate. An efficient energy minimization procedure, in which optimization of the geometry and the electron density of each subsystem is made simultaneously, is proposed and tested.

The excited-state dynamics of a series of electron donor−acceptor bridged systems (DABS) consisting of a boron−dipyrromethene chromophore covalently linked to a dinitro-substituted triptycene has been investigated using femtosecond time-resolved spectroscopy. The chromophores differ by the number of bromine atom substituents. The fluorescence lifetime of the DABS without any bromine atom is strongly reduced when going from toluene to polar solvents, this shortening being already present in chloroform. This effect is about 10 times weaker with a single bromine atom and negligible with two bromine atoms on the chromophore. The excited-state lifetime shortening is ascribed to a charge transfer from the excited chromophore to a nitrobenzene moiety, the driving force of this process depending on the number of bromine substituents. The occurrence of this process is further confirmed by the investigation of the excited-state dynamics of the chromophore alone in pure nitrobenzene. Surprisingly, no correlation between the charge separation time constant and the dielectric properties of the solvents could be observed. However, a good correlation between the charge separation time constant and the diffusional reorientation time of the chromophore alone, measured by fluorescence anisotropy, was found. Quantum chemistry calculations suggest that quasi-free rotation about the single bond linking the chromophore to the triptycene moiety permits a sufficient coupling of the donor and the acceptor to ensure efficient charge separation. The charge separation dynamics in these molecules is thus controlled by the reorientational motion of the donor relative to the acceptor.

[M(CO)₄PPh₃]^•− (M = Mo, W) were trapped at 77 K in X-irradiated single crystals of M(CO)₅PPh₃ and studied by EPR. Structures of [M(CO)₄PPh₃]^•− (M = Cr, Mo, W) were optimized by DFT; predicted g and ³¹P-hyperfine tensors agree with experiments for M = Mo, W. The anions adopt a slightly distorted pyramidal structure with PPh₃ in basal position and the spin mostly delocalized in a metal-d_z² orbital and carbon-p_z orbitals of carbonyls. The EPR tensors are slightly modified by annealing, they suggest that new constraints in the matrix distort the structure of [M(CO)₄PPh₃]^•− (M = Cr, Mo, W).

The incorporation of enantiopure 1-amino-2,3-propanediol as a subcomponent into a dicopper double helicate resulted in perfect chiral induction of the helicate's twist. DFT calculations allowed the determination of the helicity of the complex in solution. The same helical induction, in which S amines induced a Λ helical twist, was observed in the solid state by X-ray crystallography. Electronic structure calculations also revealed that the unusual deep green color of this class of complexes was due to a metal-to-ligand charge transfer excitation, in which the excited state possesses a valence delocalized Cu₂³⁺ core. The use of a racemic amine subcomponent resulted in the formation of a dynamic library of six diastereomeric pairs of enantiomers. Surprisingly, this library converted into a single pair of enantiomers during crystallization. We were able to observe this process reverse upon redissolution, as initial ligand exchange was followed by covalent imine metathesis.

We describe an advanced setup for time-resolved x-ray absorption fine structure (XAFS) Spectroscopy with picosecond temporal resolution. It combines an intense femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of the Swiss Light Source (SLS). The setup is applied to measure the short-lived high-spin geometric structure of photoexcited aqueous Fe(bpy)₃ at room temperature.

To study the electronic interactions in donor-acceptor (D-A) ensembles, D and A fragments are coupled in a single molecule. Specifically, a tetrathiafulvalene (TTF)-fused dipyrido[3,2-a:2',3'-c]phenazine (dppz) compound having inherent redox centers has been synthesized and structurally characterized. Its electronic absorption, fluorescence emission, photoinduced intramolecular charge transfer, and electrochemical behavior have been investigated. The observed electronic properties are explained on the basis of density functional theory.

The fluorine superhyperfine (shf) tensor measured in aFCl:La²⁺has been found to be practically isotropic, a result which is certainly anomalous when compared to that for em>d⁹centers with one unpaired electron in a em>x²−y²orbital. This puzzling fact has been explored by means of density functional calculations. Obtained results confirm that in the em>C_4vequilibrium geometry the unpaired electron lies in a em>b₁(∼x²−y²)orbital which overlaps with the sorbitals of four ⁻ligands. For explaining the origin of the near isotropy, which is well reproduced by the present calculations, the simple em>D_4hand i>C_4vaF₄²⁻ F₄²⁻ and gF₄²⁻centers have also been investigated. Although the obtained results stress the high dependence of the isotropic shf constant i>A_son the metal-ligand distance i>R a near isotropy of the shf tensor is only reached for aF₄²⁻(but not for F₄²⁻ under i>C_4vsymmetry which corresponds to the actual symmetry of the a²⁺center in the BaFCl lattice. The origin of this peculiar situation is shown to come from the mixing between dand forbitals of a²⁺allowed in i>C_4vsymmetry thus stressing the role played by forbitals in bonding properties. Writing i>A_s=CR^−n_sit is shown that for the i>D_4haF₄²⁻and F₄²⁻complexes the exponent i>n_sis around 20, while it is only equal to 4 for gF₄²⁻ This huge difference is shown to stem from the quite distinct slope of the radial i>dwave function at the equilibrium distance for the two i>d¹centers and the i>d⁹gF₄²⁻unit. Finally, the present calculations strongly support that the intense band peaked at 7  890  cm⁻¹recorded in the optical absorption spectrum of aFCl:La²⁺is indeed a d→4ftransition.

Several monouranium and diuranium polyhydride molecules were investigated using quantum chemical methods. The infrared spectra of uranium and hydrogen reaction products in condensed neon and pure hydrogen were measured and compared with previous argon matrix frequencies. The calculated molecular structures and vibrational frequencies were used to identify the species present in the matrix. Major new absorptions were observed and compared with the previous argon matrix study. Spectroscopic evidence was obtained for the novel complex, UH₄(H₂)₆, which has potential interest as a metal hydride with a large number of hydrogen atoms bound to uranium. Our calculations show that the series of complexes UH₄(H₂)_1,2,4,6 are stable.

The opposite orientation of the ester spacers in the rodlike ligands L 4^C12 (benzimidazole-OOC-phenyl) and L 5^C12 (benzimidazole-COO-phenyl) drastically changes the electronic structure of the aromatic systems, without affecting their meridional tricoordination to trivalent lanthanides, Ln^III, and their thermotropic liquid crystalline (i.e., mesomorphic) behaviors. However, the rich mesomorphism exhibited by the complexes [Ln(L 4^C12)(NO₃)₃] (Ln=La-Lu) vanishes in [Ln(L 5^C12)(NO₃)₃], despite superimposable molecular structures and comparable photophysical properties. Density functional theory (DFT) and time-dependant DFT calculations performed in the gas phase show that the inversion of the ester spacers has considerable effects on the electronic structure and polarization of the aromatic groups along the strands, which control residual intermolecular interactions responsible for the formation of thermotropic liquid-crystalline phases. As a rule of thumb, an alternation of electron-poor and electron-rich aromatic rings favors intermolecular interactions between the rigid cores and consequently mesomorphism, a situation encountered for L 4^C12, L 5^C12, [Ln(L 4^C12)(NO₃)₃], but not for [Ln(L 5^C12)(NO₃)₃]. The intercalation of an additional electron-rich diphenol ring on going from [Ln(L 5^C12)(NO₃)₃] to [Ln(L 6^C12)(NO₃)₃] restores mesomorphism despite an unfavorable orientation of the ester spacers, in agreement with our simple predictive model.

We report an in-depth theoretical study of 4-styrylpyridine in its singlet S₀ ground state. The geometries and the relative stabilities of the trans and cis isomers were investigated within density functional theory (DFT) as well as within Hartree-Fock (HF), second-order Møller-Plesset (MP2), and coupled cluster (CC) theories. The DFT calculations were performed using the B3LYP and PBE functionals, with basis sets of different qualities, and gave results that are very consistent with each other. The molecular structure is thus predicted to be planar at the energy minimum, which is associated with the trans conformation, and to become markedly twisted at the minimum of higher energy, which is associated with the cis conformation. The results of the calculations performed with the post-HF methods approach those obtained with the DFT methods, provided that the level of treatment of the electronic correlation is high enough and that sufficiently flexible basis sets are used. Calculations carried out within DFT also allowed the determination of the geometry and the energy of the molecule at the biradicaloid transition state associated with the thermal cis ↔trans isomerization and at the transition states associated with the enantiomerization of the cis isomer and with the rotations of the pyridinyl and phenyl groups in the trans and cis isomers. Car-Parrinello molecular dynamics simulations were also performed at 50, 150, and 300 K using the PBE functional. The studies allowed us to evidence the highly flexible nature of the molecule in both conformations. In particular, the trans isomer was found to exist mainly in a nonplanar form at finite temperatures, while the rotation of the pyridinyl ring in the cis isomer was incidentally observed to take place within ≈1 ps during the simulation carried out at 150 K on this isomer.

The ground state properties and absorption spectra of N-benzylideneaniline (NBA) have been studied at the density functional (DFT) and at the time-dependent density functional (TD-DFT) level of the theory. The equilibrium geometries of the E and Z isomers in the ground state and their vibrational frequencies have been computed. Furthermore, the excitation energies of the lowest excited singlet and triplet states and the potential energy curves along the torsion and the inversion isomerization coordinates were evaluated. The results are discussed in light of the available experimental data.

We argue with Kryachko's criticism [Int J Quantum Chem 2005, 103, 818] of the original proof of the second Hohenberg-Kohn theorem. The Kato cusp condition can be used to refute a "to-be-refuted" statement as an alternative to the original proof by Hohenberg and Kohn applicable for Coulombic systems. Since alternative ways to prove falseness of the "to-be-refuted" statement in a reduction ad absurdum proof do not exclude each other, Kryachko's criticism is not justified.

The ground and excited electronic state properties of calicene (triapentafulvalene or 5-(cycloprop-2-en-1-ylidene)cyclopenta-1,3-diene) have been studied with a variety of density functional models (mPWPW91, PBE, TPSS, TPSh, B3LYP) and post-Hartree−Fock models based on single (MP2 and CCSD(T)) and multideterminantal (CASPT2) reference wave functions. All methods agree well on the properties of ground-state calicene, which is described as a conjugated double bond system with substantial zwitterionic character deriving from a charge-separated mesomer in which the three- and five-membered rings are both aromatic. Although the two rings are joined by a formal double bond, contributions from the aromatic mesomer reduce its bond order substantially. A rotational barrier of 40−41 kcal mol^-1 is predicted in the gas phase and solvation effects reduce the barrier to 37 and 33 kcal mol^-1 in benzene and water, respectively, because of increased zwitterionic character in the twisted transition-state structure. Multi-state CASPT2 (MS-CASPT2) is used to characterize the first few excited singlet and triplet states and indicates that the most important transition occurs at 4.93 eV (251 nm). A cis−trans photoisomerization about the inter-ring double bond is found to be inefficient.

Structural changes of the iron(II)-tris-bipyridine ([Fe^II(bpy)₃]²⁺) complex induced by ultrashort pulse excitation and population of its short-lived (≤0.6  ns) quintet high spin state have been detected by picosecond x-ray absorption spectroscopy. The structural relaxation from the high spin to the low spin state was followed over the entire lifetime of the excited state. A combined analysis of the x-ray-absorption near-edge structure and extended x-ray-absorption fine structure spectroscopy features delivers an Fe-N bond elongation of 0.2 Å in the quintet state compared to the singlet ground state.

We present novel insight on like-spin domains (LSD) in cooperative spin transition solids by following the photo-transformation and the subsequent relaxation of a [Fe(ptz)₆](BF₄)₂ single crystal in the vicinity of the light-induced instability. Self-organization under light is observed, accompanied by Barkhausen-like noise and jumps which reveal the presence of elastic interactions between LSDs. The light-induced phase separation process is discussed in terms of a dynamic potential providing spinodal instability in the corresponding temperature range. This useful concept is applicable to all types of switchable molecular solids.

Maxing out at six: The maximum bond order that can be achieved between two equal atoms in the periodic system is six. The picture shows the potential energy curves for the diatoms Cr₂, Mo₂, and W₂, where the latter two are sextuply bonded molecules (d=internuclear distance in atomic units).

Recent advances in computational actinide chemistry are reported in this tutorial review. Muticonfigurational quantum chemical methods have been employed to study the gas phase spectroscopy of small actinide molecules. Examples of actinide compounds studied in solution are also presented. Finally the multiple bond in the diuranium molecule and other diactinide compounds is described.

The endohedral fullerene CH₄@C₈₄ has been studied using density functional theory (DFT) and second-order Møller-Plesset perturbation theory (MP2). In addition to the structure with a C— bond of CH₄ in a tetrahedral pocket conformation, we find an alternative minimum, very close in energy (6.3-9.5 kJ/mol higher according to the level of theory), with the methane inverted, which we call the antipocket conformation. Computed IR spectra are reported for CH₄@C₈₄ and also for the reference system CH₄@C₆₀. The calculated vibrational levels, in a harmonic approximation, reveal close-lying translational, librational, and shell-vibrational modes. The results are also presented for the isoelectronic species NH₄⁺@C₆₀.

Single crystal dixanthinium tetrachlorozincate has been grown from dilute chloridric acid. Polarized Raman spectrum of the single crystalline sample, FT-Raman and FT-IR spectra of the polycrystalline samples have been examined and the bands assigned to the appropriate modes predicted by a factor group analysis for the space group Pmn2₁. The crystal structure has been confirmed by powder XRD measurements.

Mixed single PbFBr_1−xI_x crystals have been prepared. X-ray powder diffraction structure determinations show that all samples crystallize with the matlockite structure. However, the single crystal structure of PbFBr_0.5I_0.5 involves not only fractional occupation of one site corresponding to the stoichiometry, but also split positions of the Pb²⁺ ion. Raman spectra reveal the presence of new additional bands with respect to PbFBr and PbFI. DFT calculations of lattice vibrations for PbFI show good agreement with experimental spectra. The calculated phonon dispersion curve suggests that for the mixed crystals the centre of inversion is conserved locally. These combined results suggest the presence of domains with ordered F–Pb–Br–Br–Pb–F and F–Pb–I–I–Pb–F layers in the mixed crystals. Calculations on PbFBr_0.5I_0.5 show that this suggested structure is more stable than the structure consisting of the F–Pb–Br–I–Pb–F arrangement.

Whereas there are hundreds of known iron(II) spin-crossover compounds, only a handful of cobalt(II) spin-crossover compounds have been discovered to date, and hardly an in depth study on any of them exists. This review begins with an introduction into the theoretical aspects to be considered when discussing spin-crossover compounds in general and cobalt(II) systems in particular. It is followed by case studies on [Co(bpy)₃]²⁺ and [Co(terpy)₂]²⁺ (bpy = 2,2′-bipyridine, terpy = 2,2′:6′,2″-terpyridine) presenting and discussing results from magnetic susceptibility measurements, X-ray crystallography, optical spectroscopy, and EPR spectroscopy.

A combination of attenuated total reflection infrared (ATR-IR) and modulation excitation spectroscopy (MES) is used to study the enantiodiscriminating interactions between proline and a chiral, self-assembled monolayer (SAM) of N-acetyl-L-cysteine on gold. The N-acetyl-L-cysteine SAM consists of a mixture of protonated and deprotonated molecules. Whereas both species are influenced by adsorbed proline, only the deprotonated molecules are involved in enantiodiscrimination. Density functional theory (DFT) calculations reveal that electrostatics dominates the interaction between the two molecules. By modulating the absolute configuration of proline over the chiral SAM, and a subsequent phase-sensitive detection of the periodically varying signals in the ATR-IR spectra, the small spectral differences between the diastereomeric complexes are spotted. The resulting difference spectrum is in qualitative agreement with the spectrum predicted by the DFT calculations.

Optically active liquid-crystalline side-chain polysiloxanes have been prepared by grafting planar chiral ferrocene-based vinyl monomers onto commercially available polyhydrosiloxane. Two ferrocene monomers have been synthesized: a linear-type monomer, which displays a monotropic chiral smectic C (S_C*) phase and enantiotropic smectic A (S_A) and chiral N (N*) phases, and a laterally branched monomer, which shows an enantiotropic N* phase. X-ray diffraction analysis indicates a monomolecular organization of the monomeric units within the smectic layers. The polymers retain the liquid-crystalline phases of their corresponding monomers. The UV-vis and circular dichroism (CD) spectra are in agreement with the structure of the monomers and polymers. The molar absorption coefficient (ϵ) and molar circular dichroic absorption coefficient (Δϵ) values of the polymers are proportional to the number of monomeric units grafted onto them. The absolute configuration of the ferrocene carboxylic acid intermediate, used to synthesize the monomers, has been determined on the basis of CD spectra. The helical twisting power (HTP) of the nematogenic monomer and polymer have been determined in E7, and indicate that such materials could be used as chiral dopants. Finally, this study demonstrates that the nature of chiral phases can be controlled by structural engineering of the organic groups only, with ferrocene acting as the source of chirality.

A method for in situ monitoring of surface and gas species utilizing separately the difference and sum reflectivity of two polarizations, normal and parallel to the surface, measured by polarization-modulation infrared reflection-absorption spectroscopy is presented. Surface and gas-phase spectra were separately but simultaneously obtained from the reflectivities. The technique is combined with modulation excitation spectroscopy to further enhance the sensitivity, and a small-volume cell was designed for this purpose. CO oxidation over a 40 nm Pt film on aluminum was investigated under moderate pressure (atmospheric pressure, 5% CO, and 5%–40% O₂) at 373–433 K. The surface species involved in the oxidation process and the gas-phase species, both reactant (CO) and product (CO₂), could be simultaneously monitored and analyzed quantitatively. In addition, the reflectivity change of the sample during the reaction was assigned to a near-surface bulk property change, that is, surface reconstruction to the oxide phase. Under an O₂-rich atmosphere, two reactive phases, denoted as low- and high-activity phases, were identified. A large amount of atop CO was observed during the low-activity phase, while the adsorbed CO completely disappeared during the high-activity phase. The presence of an infrared-inactive CO₂ precursor formed by the reaction between surface oxide and gaseous CO during the high-activity phase was inferred. The desorption of the CO₂ precursor is facilitated under a CO-rich atmosphere, most likely, by surface reconstruction to metallic Pt and a competitive adsorption of CO on the surface.

The adsorption of L-glutathione (γ-Glu-Cys-Gly) from ethanol on gold surfaces was studied in situ by both attenuated total reflection infrared (ATR-IR) spectroscopy and using a quartz crystal microbalance (QCM). The molecule is firmly anchored to the gold surface through the thiol group. Different IR signals of adsorbed L-glutathione, notably the amide I and ν(–COOH), show significantly different behavior with time, which reveals that their increase is not related to adsorption (mass uptake) alone. This indicates that structural transformations take place during the formation of the self-assembled monolayer (SAM). In particular, the intensity of the acid signal increases quickly only within the first couple of minutes. The complexity of the self-assembling process is confirmed by QCM measurements, which show fast mass uptake within about 100 s followed by a considerably slower regime. The structural change superimposed on the mass uptake is, based on the in situ time-resolved ATR-IR measurements, assigned to the interaction of the acid group of the Gly moiety with the surface. The latter group is protonated in ethanol but deprotonates upon interaction with the gold surface. The protonation–deprotonation equilibrium is sensitive to external stimuli, such as the presence of dissolved L-glutathione molecules. The interaction of the acid group with the surface and concomitant deprotonation proceeds via two distinguishable steps, the first being a reorientation of the molecule, followed by the deprotonation.

Square-wave stimulation used in modulation excitation spectroscopy [D. Baurecht, U.P. Fringeli, Rev. Sci. Instrum. 72 (2001) 3782] can have significant advantages over a simple sinusoidal-wave due to the high odd-frequency terms contained in square-wave, particularly when a system response is close to linear. Phase-sensitive detection (PSD) affords separating the signals of the different frequency terms with a high signal-to-noise ratio by averaging a number of modulation cycles. A modulation excitation experiment applying square-wave stimulation provides the same information as several experiments applying sinusoidal-wave stimulations at the same frequency as the square-wave stimulation and at higher frequencies. The amplitude and the phase lag of a response obtained by PSD at fundamental and higher frequencies using square-wave stimulation are related to the ones obtained by sinusoidal-wave stimulation using transfer function of a general system. Mixing property of a PM-IRRAS (polarization–modulation infrared reflection–absorption spectroscopy) flow-through cell was studied by a simple mixing tank model using square-wave concentration stimulation. The advantages of square-wave stimulation are shown by the characterization of the mixing property.

Polarization-modulation infrared reflection-absorption spectroscopy (Pm-irras) is a sensitive tool for the analysis of species residing at gas-solid and gas-liquid interfaces. the polarization-modulation allows excellent back-ground compensation and the analysis of surface/interface species under moderate pressure (e.g. atmospheric pressure of ir-absorbing gases) is possible. we demonstrate a new possibility to extract simultaneously information of gas and solid phases in addition to surface species from the Pm-irras experiments, using co oxidation over Pt film as an example. modulation excitation spectroscopy (mes) has been combined with this technique to enhance the sensitivity and to analyze the kinetic behavior of species. the surface species involved in the oxidation process, the state of Pt, and the gas phase species (co and co₂) could be simultaneously monitored in situ and analyzed quantitatively. the technique can serve as a valuable tool for investigations of various dynamic phenomena occurring at gas-solid interfaces.

The enantiomers of tert-butyl(dimethylamino)phenylphosphine−borane complex 2 have been separated by HPLC using cellulose tris-p-methylbenzoate as chiral stationary phase. The borane protection could be removed without racemization and the P-configuration of the free aminophosphine 1 has shown to be stable in solution. Infrared (IR) and vibrational circular dichroism (VCD) spectra have been measured in CD₂Cl₂ solution for both enantiomers. B3LYP/6-31+G(d) DFT calculations allowed a prediction that complex (S)-2 exists as three conformers in equilibrium and computed population-weighted IR and VCD spectra. Predicted and experimental IR and VCD spectra compared very well and indicate that enantiomer (+)-2 has the S absolute configuration. This assignment has been confirmed by an X-ray diffraction study on a single crystal of (+)-2. The crystal structure of enantiomerically pure 2 appears to be very close to the most stable computed conformer which proved to be predominant in solution.

The photoassisted mineralization, i.e., conversion to CO₂ and water, of malonic acid over P25 TiO₂ was investigated by in situ attenuated total reflection infrared (ATR-IR) spectroscopy in a small volume flow-through cell. Reassignment of the vibrational bands of adsorbed malonic acid, assisted by deuterium labeling, reveals two dissimilar carboxylate groups within the molecule. This indicates adsorption via both carboxylate groups, one in a bridging or bidentate and the other in monodentate coordination. During irradiation the coverage of malonic acid strongly decreases, and oxalate is observed on the surface in at least two different adsorption modes. The major oxalate species observed during irradiation is characterized by monodentate coordination of both carboxylate groups. In the dark, however, part of these species adopts another adsorption mode, possibly interacting only with one carboxylate group. During band gap illumination a large fraction of the surface is not covered by acid. Oxalate is a major intermediate in the mineralization of malonic acid. However, the observed transient kinetics of adsorbed malonic and oxalic acid indicates additional pathways not involving oxalate. The rate constant for oxalate decomposition is slightly larger than the one for oxalate formation from malonic acid. As the oxalate is desorbing slowly from the surface its concentration in the liquid phase is small, despite the fact that it is a major intermediate in the mineralization of malonic acid.

We have prepared gold nanoparticles covered with N-isobutyryl-l-cysteine and N-isobutyryl-d-cysteine, respectively. These particles with a mean particle size smaller than 2 nm are highly soluble in water and are amenable to chiroptical techniques such as vibrational circular dichroism (VCD) and circular dichroism (CD) spectroscopy. Density functional theory shows that the VCD spectra are sensitive toward the conformation of the adsorbed thiol. Based on the comparison between the experimental VCD spectrum and the calculated VCD spectra for different conformers, a preferential conformation of the thiol adsorbed on the gold particles can be proposed. In this conformation the carboxylate group interacts with the gold particle in addition to the sulfur. The particles could furthermore be separated according to their charge and size into well-defined compounds. The optical absorption spectra revealed a well-quantized electronic structure and a systematic red-shift of the absorption onset with increasing gold core size, which was manifested in a color change with particle size. Some compounds showed basically identical absorption spectra as analogous gold particles protected with l-glutathione. This shows that these particles have identical core sizes (10−12, 15 and 18 gold atoms, respectively) and indicates that the number and arrangement of the adsorbed thiol are the same, independent of the two thiols, which have largely different sizes. Some separated compounds show strong optical activity with opposite sign when covered with the d- and l-enantiomer, respectively, of N-isobutyryl-cysteine. The origin of the optical activity in the metal-based transitions is discussed. The observations are consistent with a mechanism based on a chiral footprint on the metal core imparted by the adsorbed thiol.

The adsorption of penicillamine from ethanol on gold was studied in situ by attenuated total reflection infrared (ATR-IR) and quartz crystal microbalance (QCM) experiments. Both ATR-IR and QCM reveal a fast mass uptake. In ethanol, the molecule adopts a zwitterionic form. Upon adsorption, part of the molecules deprotonate at the amine group, which is a relatively slow process that goes along with a strong shift of the ν_as(COO^-) mode. Both ATR-IR and QCM confirm a physisorbed layer. ATR-IR furthermore shows that the latter consists of zwitterionic molecules only, whereas both zwitterionic and anionic species are found in the chemisorbed layer. The infrared spectra of the physisorbed and chemisorbed layers are rather different, and the molecules within both layers seem to be oriented with respect to the surface. The ATR-IR spectra furthermore indicate that all three functional groups of penicillamine (i.e., thiol, carboxylate, and amine) interact with the surface, and density functional theory calculations support this finding. QCM also shows that the molecule uses considerably more space on the surface than molecules of similar size, which supports a three-point interaction. The latter leads to a strong anchoring of the molecule to the metal, which may explain the exceptional capability of penicillamine to bind metals.

Chiral metal surfaces and nanoparticles have the potential to be used for the selective production, the resolution and the detection of enantiomers of a chiral compound, which renders them highly attractive in view of the tremendous consequences of homochirality on earth. Their capability to distinguish between enantiomers of a chemical compound relies on their structure and the ability to form intermolecular interactions. However, molecular-level understanding of the interactions that are at the origin of enantiodiscrimination is lagging behind due to the lack of powerful experimental techniques that are able to spot these interactions selectively with high sensitivity. In this article two techniques based on infrared spectroscopy are presented that are able to selectively target the chiral properties of nanoparticles and interfaces. These are the combination of attenuated total reflection infrared (ATR-IR) with modulation excitation spectroscopy (MES) to probe enantiodiscriminating interactions at chiral solid-liquid interfaces and vibrational circular dichroism (VCD), which is used to probe the structure of chirally modified metal nanoparticles.

Attenuated total reflection (ATR) infrared (IR) spectroscopy is a powerful tool for investigation of solid catalysts, allowing the detection of liquid-phase products (for on-line reaction monitoring) and the investigation of species adsorbed on the catalyst, during reaction and in the presence of strongly absorbing solvents. Flat model catalysts such as metal films as well as powder catalysts can be investigated. In favorable situations, even changes of the catalyst structure can be followed. In this review, some fundamental concepts of ATR spectroscopy are summarized, and practical aspects, such as cell design and sample preparation, are discussed. The potential and limitations of the method are illustrated with examples. Furthermore, powerful techniques aimed at enhancing signal-to-noise ratios and long-term stability are described, which make use of phase-sensitive detection of periodically varying signals and accurate reference measurements. Until now, only a rather limited number of investigations have been reported that use the ATR technique to study heterogeneous catalytic reactions at solid–liquid interfaces, but the method holds good promise because it is comparatively inexpensive and versatile and can provide a large amount of information.

Density functional theory (DFT) has progressively emerged in the last 40 years as a leading methodology for the modelling and simulation of chemical systems. In this paper, some historical landmarks in the development of this method are outlined, emphasizing on its main characteristic being an electron density-based theory. This is in contrast with wavefunction-based methodologies which were exclusively employed previously. Interestingly, DFT has been first applied to solids, with a rather late recognition by chemists and molecular scientists. After this historical survey, several applications of DFT to the structure and properties of zeolites are reviewed as a tribute to Dr Annick Goursot.

Neutral, radical [CpNi(dithiolene)] complexes fused with seven-membered rings, formulated as [CpNi{S₂C₂S₂(CH₂)₂X}] (X = CH₂, CF₂, C=CH₂, S), have been synthesized in 30-60 % yields from the reactions of nickelocene with the corresponding neutral, square-planar, (dithiolene)nickel complexes [Ni{S₂C₂S₂(CH₂)₂X}₂]. [CpNi{S₂C₂S₂(CH₂)₂X}] (X = C=O) was prepared from nickelocene and [1,3]dithiolo[4,5-b][1,4]dithiepine-2,6-dione under thermal or photochemical conditions. All complexes exhibit reversible oxidation and reduction waves to the cation and anion form, respectively. The terminal groups (X) in the seven-membered ring shift their redox potentials to anodic potentials in the following order: CF₂ > C=O > S > C=CH₂ > CH₂. The singlet EPR responses of [CpNi{S₂C₂S₂(CH₂)₂(X)}] appear at g ≈ 2.0514-2.0529 in dichloromethane solution at room temperature. An NIR absorption is observed at λ_max ≈ 798-848 nm (ε ≈ 1700-2400 sup>-1 cm^-1) in dichloromethane solution. The X-ray structures of the five complexes show two-legged piano-stool geometries around the central nickel atom (formally Ni^III) and strong distortions from planarity of the seven-membered C₂S₂(CH₂)₂X rings. In the solid state, those radical (S = 1/2) species adopt either one-dimensional alternating chain-like motifs (X = CH₂, C=CH₂, S) or dimeric entities characterized by a singlet-triplet magnetic behavior (X = CF₂, C=O).

Circular dichroism (CD) spectra and density functional theory (DFT) calculations are reported for a series of conformationally bistable chiroporphyrins with 8-methylene bridles MBCP-8, which can display either an αααα or an αβαβ orientation of their meso substituents. From DFT geometry optimizations, the most stable form of ZnBCP-8 is found to be the αααα conformer. By passing to NiBCP-8, there is a strong stabilization of the αβαβ conformation with respect to the αααα conformation, consistent with the X-ray structures of αααα-ZnBCP-8 and αβαβ-NiBCP-8. A correlation between the sign of the CD signal in the Soret region and the conformation of the BCP-8 compounds is reported: the αααα conformers H₂BCP-8 and ZnBCP-8 show a positive CD signal, whereas the αβαβ conformers NiBCP-8 and CuBCP-8 exhibit a negative signal. The possible contributions to the rotational strengths of αβαβ-NiBCP-8 and αααα-ZnBCP-8, calculated on the basis of their crystal structures, have been analyzed. The CD signals are found to result from a combination of both the inherent chirality of the porphyrin and of extrinsic contributions due to the chiral bridles. These results may have a broad significance for understanding the chiroptical properties of chiral porphyrins and hemoproteins and for monitoring stimuli-responsive, conformationally bistable chiroporphyrin compounds.

Photoswitching of the dielectric constant has been observed for the first time in the spin-crossover complex [Fe(L)(CN)₂]·H₂O (L=2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, see picture). The electrical detection of a photoinduced change in spin state could allow the use of such complexes in optical information-storage devices.

Frequency shifts of the Ag  I  4d¹⁰5s  ²S_1∕2(F=0,M_F=0) to 4d⁹5s^{2  2}D_5∕2(F^′=2,M_F^′=0) electric-quadrupole transition at 330.6  nm due to external fields are calculated using multiconfigurational self-consistent field methods. As this forbidden transition is free from first order Doppler and Zeeman effects, it is under investigation for the realization of an atomic optical clock. The calculated perturbations are the light shift, the blackbody frequency shift, and the quadratic Zeeman shift. Results show that a total uncertainty of 10⁻¹⁸ could be reach without confining the atoms in a Lamb-Dicke regime in an optical lattice.

The bifunctional of the nonadditive kinetic energy in the reference system of noninteracting electrons ( T^nad_s [ρ_A, ρ_B] = T_s[ρ_A + ρ_B] − T_s[ρ_A] − T_s[ρ_B]) is the key quantity in orbital-free embedding calculations because they hinge on approximations to T^nad_s [ρ_A,ρ_B]. Since T^nad_s [ρ_A,ρ_B] is not linear in ρ_A, the associated potential (functional derivative) T^nad_s [ρ,ρ_B]/δρ|_ρ=ρA(r^→) changes if ρ_A varies. In this work, for two approximations to T^nad_s [ρ_A,ρ_B], which are nonlinear in ρ_A (gradient-free and gradient-dependent), their linearized versions are constructed, and the resulting changes (linearization errors) in various properties of embedded systems (orbital energies, dipole moments, interaction energies, and electron densities) are analyzed. The considered model embedded systems represent typical nonbonding interactions: van der Waals contacts, hydrogen bonds, complexes involving charged species, and intermolecular complexes of the charge-transfer character. For van der Waals and hydrogen bonded complexes, the linearization of T^nad_s [ρ_A,ρ_B] affects negligibly the calculated properties. Even for complexes, for which large complexation induced changes of the electron density can be expected, such as the water molecule in the field of a cation, the linearization errors are about 2 orders of magnitude smaller than the interaction induced shifts of the corresponding properties. Linearization of T^nad_s [ρ_A,ρ_B] is shown to be inadequate for the complexes of a strong charge-transfer character. Compared to gradient-free approximation to T^nad_s [ρ_A,ρ_B], introduction of gradients increases the linearization error.

About 3 µm thick tungsten trioxide film electrodes consisting of partly sintered, 40-80 nm in diameter, particles deposited on conducting glass substrates exhibit high photon-to-current conversion efficiencies for the photooxidation of water, exceeding 70% at 400 nm. This is facilitated by a ca. 40% film porosity resulting in high contact area with the electrolyte. It is shown that the activity of the WO₃ electrodes towards photooxidation of water is enhanced by addition of even small amounts of halide (Cl^-, Br^-) ions to the acidic electrolyte. Photoelectrolysis experiments performed either in acidic electrolytes containing chloride or bromide anions or in a 0.5 M NaCl solution, under simulated 1.5 AM solar illumination, demonstrated long term stability of the photocurrents. Oxygen remains the main product of the photoanodic reaction even in a 0.5 M NaCl solution, a composition close to the sea water, with chlorine accounting for ca. 20% of current efficiency.

Ultrafast infrared transient absorption spectroscopy is used to study the photoinduced bimolecular electron transfer reaction between perylene in the first singlet excited state and 1,4-dicyanobenzene in acetonitrile and dichloromethane. Following vibrational marker modes on both donor and acceptor sides in real time provides direct insight into the structural dynamics during the reaction. A band narrowing on a time scale of a few tens of picoseconds observed on the antisymmetric CN stretching vibration of the dicyanobenzene radical anion indicates that a substantial part of the excess energy is channeled into vibrational modes of the product, despite the fact that the reaction is weakly exergonic. An additional narrowing of the same band on a time scale of several hundreds of picoseconds observed in acetonitrile only is interpreted as a signature of the dissociation of the geminate ion pairs into free ions.

Multiconfigurational quantum chemical methods (CASSCF/CASPT2) have been used to study the chemical bond in the actinide diatoms Ac₂, Th₂, Pa₂, and U₂. Scalar relativistic effects and spin−orbit coupling have been included in the calculations. In the Ac₂ and Th₂ diatoms the atomic 6d, 7s, and 7p orbitals are the significant contributors to the bond, while for the two heavier diatoms, the 5f orbitals become increasingly important. Ac₂ is characterized by a double bond with a ³∑_g^-(0_g⁺) ground state, a bond distance of 3.64. Å, and a bond energy of 1.19 eV. Th₂ has quadruple bond character with a ³D_g(1_g) ground state. The bond distance is 2.76 Å and the bond energy (D₀) 3.28 eV. Pa₂ is characterized by a quintuple bond with a ³∑_g^-(0_g⁺) ground state. The bond distance is 2.37 Å and the bond energy 4.00 eV. The uranium diatom has also a quintuple bond with a ⁷O_g (8_g) ground state, a bond distance of 2.43 Å, and a bond energy of 1.15 eV. It is concluded that the strongest bound actinide diatom is Pa₂, characterized by a well-developed quintuple bond.

The separation of different ring numbered polyaromatic hydrocarbons (PAHs) was accomplished by using cetyltrimethylammonium bromide (CTAB) in capillary electrokinetic chromatography. In order to increase the solubilities and selectivities of PAHs, acetonitrile (ACN) was used as an organic modifier. Under the optimised conditions, 11 aromatic compounds were separated within 14.5 min in a running electrolyte containing 10 mM phosphate, 30 mM CTAB, and 40% ACN at pH 6.0. The effects of CTAB and ACN concentrations, voltage and pH on the resolution were investigated. Reproducibilities of migration times range between 0.55 and 1.27 R.S.D.% and peak areas between 1.02 and 7.23 R.S.D.%. Limit of detections (LODs) range between 0.09 and 2.24 μg ml⁻¹. This new and fast separation method of PAHs was applied to cooked oil sample.

One-electron reduction of a diphosphafulvenium dication gives the first stable diphosphafulvenium monoradical cation (see scheme). An X-ray crystal structure analysis, EPR measurements, and DFT calculations clearly show that reduction takes place at the exocyclic double bond and that the excess of electron density is stabilized by the two electron-withdrawing phosphonium groups (see SOMO; P orange, C dark gray, H light gray).

A series of molybdenum and tungsten nitrido, [M(N)(X)(diphos)₂], and imido complexes, [M(NH)(X)(diphos)₂)]Y, (M = Mo, W) with diphosphine coligands (diphos = dppe/depe), various trans ligands (X = N₃^-, Cl^-, NCCH₃) and different counterions (Y^- = Cl^-, BPh₄^-) is investigated. These compounds are studied by infrared and Raman spectroscopies; they are also studied with isotope-substitution and optical-absorption, as well as emission, spectroscopies. In the nitrido complexes with trans-azido and -chloro coligands, the metal−N stretch is found at about 980 cm^-1; upon protonation, it is lowered to about 920 cm^-1. The ¹A₁ → ¹E (n → π*) electronic transition is observed for [Mo(N)(N₃)(depe)₂] at 398 nm and shows a progression in the metal−N stretch of 810 cm^-1. The corresponding ³E → ¹A (π* → n) emission band is observed at 542 nm, exhibiting a progression in the metal−N stretch of 980 cm^-1. In the imido system [Mo(NH)(N₃)(depe)₂]BPh₄, the n → π* transition is shifted to lower energy (518 nm) and markedly decreases in intensity. In the trans-nitrile complex [Mo(N)(NCCH₃)(dppe)₂]BPh₄, the metal−N(nitrido) stretching frequency increases to 1016 cm^-1. The n → π* transition now is found at 450 nm, shifting to 525 nm upon protonation. Most importantly, the reduction of this nitrido trans-nitrile complex is drastically facilitated compared to its counterparts with anionic trans-ligands (E_p^red = −1.5 V vs Fc⁺/Fc). On the other hand, the basicity of the nitrido group is decreased (pK_a{[Mo(NH)(NCCH₃)(dppe)₂](BPh₄)₂} = 5). The implications of these findings with respect to the Chatt cycle are discussed.

State-of-the-art generalized gradient approximation (GGA) (PBE, OPBE, RPBE, OLYP, and HCTH), meta-GGA (VSXC and TPSS), and hybrid (B3LYP, B3LYP*, O3LYP, and PBE0) functionals are compared for the determination of the structure and the energetics of the D₃ [Co(bpy)₃]²⁺ complex in the ⁴A₂ and ⁴E trigonal components of the high-spin ⁴T_1g( t⁵_2g e²_g ) state and in the low-spin ²E state of octahedral ²E_g( t⁶_2g e¹_g) parentage. Their comparison extends also to the investigation of the Jahn−Teller instability of the ²E state through the characterization of the extrema of C₂ symmetry of this spin state's potential energy surface. The results obtained for [Co(bpy)₃]²⁺ in either spin manifold are very consistent among the functionals used and are in good agreement with available experimental data. The functionals, however, perform very differently with respect to the spin-state energetics because the calculated values of the high-spin/low-spin energy difference ΔE^el_HL vary between −3212 and 3919 cm^-1. Semilocal functionals tend to give too large ΔE^el_HL values and thus fail to correctly predict the high-spin state as the ground state of the isolated complex, while hybrid functionals tend to overestimate the stability of the high-spin state with respect to the low-spin state. Reliable results are, however, obtained with the OLYP, HCTH, B3LYP*, and O3LYP functionals which perform best for the description of the isolated complex. The optical properties of [Co(bpy)₃]²⁺ in the two spin states are also analyzed on the basis of electronic excitation calculations performed within time-dependent density functional response theory. The calculated absorption and circular dichroism spectra agree well with experimental results.

A new 1,3-dithiol-2-ylidene substituted naphthopyranone 2 has been synthesized and characterized. UV–vis spectroscopic and cyclic voltammetry results, interpreted on the basis of density functional theory, show that 2 displays an intramolecular charge-transfer transition and acts like a donor–acceptor (D–A) system. Furthermore, a weak fluorescence originating from the excited charge-transfer state is observed.

Luminophors of the perylene series containing the N,N-dimethylaniline residue in their molecules have been synthesised for the first time; spectral and luminescent properties of these compounds have been studied

Various preparations of the neutral radical [CpNi(dddt)] complex (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were investigated with CpNi sources, [Cp₂Ni], [Cp₂Ni](BF₄), [CpNi(CO)]₂, and [CpNi(cod)](BF₄), and dithiolene transfer sources, O=C(dddt), the naked dithiolate (dddt^2-), the monoanion of square-planar Ni dithiolene complex (NBu₄)[Ni(dddt)₂], and the neutral complex [Ni(dddt)₂]. The reaction of [CpNi(cod)](BF₄) with (NBu₄)[Ni(dddt)₂] gave the highest yield for the preparation of [CpNi(dddt)] (86%). [CpNi(ddds)] (ddds = 5,6-dihydro-1,4-dithiin-2,3-diselenolate), [CpNi(dsdt)] (dsdt = 5,6-dihydro-1,4-diselenin-2,3-dithiolate), [CpNi(bdt)] (bdt = 1,2-benzenedithiolate), and [CpNi(bds)] (bds = 1,2-benzenediselenolate) were synthesized by the reactions of [Cp₂Ni] with the corresponding neutral Ni dithiolene complexes [Ni(ddds)₂]₂, [Ni(dsdt)₂], [Ni(bdt)₂], and [Ni(bds)₂], respectively. The five, formally Ni^III, radical complexes oxidize and reduce reversibly. They exhibit, in the neutral state, a strong absorption in the NIR region, from 1000 nm in the dddt/ddds/dsdt series to 720 nm in the bdt/bds series with ε values between 2500 and 5000 M^-1 cm^-1. The molecular and solid state structures of the five complexes were determined by X-ray structure analyses. [CpNi(dddt)] and [CpNi(ddds)] are isostructural, while [CpNi(dsdt)] exhibits a closely related structure. Similarly, [CpNi(bdt)] and [CpNi(bds)] are also isostructural. Correlations between structural data and magnetic measurements show the presence of alternated spin chains in [CpNi(dddt)], [CpNi(ddds)], and [CpNi(dsdt)], while a remarkably strong antiferromagnetic interaction in [CpNi(bdt)] and [CpNi(bds)] is attributed to a Cp···Cp face-to-face σ overlap, an original feature in organometallic radical complexes.

The binding of N-heterocyclic carbenes to Ce(III) and U(III) compounds is characterized by quantum chemical methods. Density functional methods are in qualitative agreement with experiment that binding to U(III) is more favorable than to Ce(III); after correcting for basis-set superposition error, quantitative agreement with experiment is achieved with a multireference second-order perturbation theory approach accounting for relativistic effects. The small computed (and observed) preference derives from a combination of several small effects, including differences in electronic binding energies, rovibrational partition functions, and solvation free energies. Prospects for ligand modification to improve the differentiation between lanthanides and actinides are discussed on the basis of computational predictions.

The relative energetics of μ-η¹:η¹ (trans end-on) and μ-η²:η² (side-on) peroxo isomers of Cu₂O₂ fragments supported by 0, 2, 4, and 6 ammonia ligands have been computed with various density functional, coupled-cluster, and multiconfigurational protocols. There is substantial disagreement between the different levels for most cases, although completely renormalized coupled-cluster methods appear to offer the most reliable predictions. The significant biradical character of the end-on peroxo isomer proves problematic for the density functionals, while the demands on active space size and the need to account for interactions between different states in second-order perturbation theory prove challenging for the multireference treatments. In the latter case, it proved impossible to achieve any convincing convergence.

The crystal structure of the disordered modification of Ba₇F₁₂Cl₂ has been carefully re-examined on several new crystals prepared under different conditions of synthesis. All single crystal structure refinements reveal a residual electron density of ~3 e^-/ų in the 0,0,0 position which is explained by the introduction of a small amount of sodium ions in the crystal. The title compound transforms from a disordered to an ordered modification at ~800 °C. New structural data show a change in space group from P6₃/m to P6. During this process, a slight chemical change and the formation of nano-channels in the crystals is observed by electron microscopy. These changes were further studied by electron microprobe analysis, by spectroscopic methods and thermal analysis.

Nice to see U₂! The [PhUUPh] molecule (see picture; U pink, C gray, H white) has been studied by multiconfigurational quantum chemical methods. It was found that a quintuple bond is formed between the two uranium atoms with a U—U bond length of 2.29 Å. The phenyl ligand was used to mimic a bulky terphenyl ligand, which could be a promising candidate for the stabilization of multiply bonded uranium compounds.

Paramagnetic complexes M(CO)₅P(C₆H₅)₂, with M = Cr, Mo, W, have been trapped in irradiated crystals of M(CO)₅P(C₆H₅)₃ (M = Cr, Mo, W) and M(CO)₅PH(C₆H₅)₂ (M = Cr, W) and studied by EPR. The radiolytic scission of a P−C or a P−H bond, responsible for the formation of M(CO)₅P(C₆H₅)₂, is consistent with both the number of EPR sites and the crystal structures. The g and ³¹P hyperfine tensors measured for M(CO)₅P(C₆H₅)₂ present some of the characteristics expected for the diphenylphosphinyl radical. However, compared to Ph₂P^•, the ³¹P isotropic coupling is larger, the dipolar coupling is smaller, and for Mo and W compounds, the g-anisotropy is more pronounced. These properties are well predicted by DFT calculations. In the optimized structures of M(CO)₅P(C₆H₅)₂ (M = Cr, Mo, W), the unpaired electron is mainly confined in a phosphorus p-orbital, which conjugates with the metal d_xz orbital. The trapped species can be described as a transition metal-coordinated phosphinyl radical.

Quantum chemistry can today be employed to invent new molecules and explore unknown molecular bonding. An overview of novel species containing metals bound to polynitrogen clusters is presented. The prediction of metal polyhydrides is discussed. Finally, some species containing gold that behaves as a halogen are described, together with recent advances in actinide chemistry and exploration of the nature of the actinide–actinide chemical bonding.

Vibrational spectra of BH₄^- and its isotopic analogues in a crystalline environment of alkali metals cations (K⁺, Rb⁺, Cs⁺) have been investigated beyond the harmonic approximation using a variational approach supported by computations of B3LYP type anharmonic force fields. From the comparison of the observed and simulated IR spectra, the influence of the anharmonic couplings on the band position and on the relative intensity of the allowed vibrational transitions is discussed. Here, the effect of the crystalline environment induces a blue shift of about 50 and 100 cm^-1 respectively for the bending and stretching modes of BH₄^-. Furthermore, anharmonic effects, which are exclusively well reproduced by a variational approach, are needed to yield reliable positions and relative amplitudes of IR allowed combination and overtone transitions. This leads to theoretical results fitting their experimental counterpart between 6 and 30 cm^-1 in the investigated series.

A series of 6-styryl-2,4-diphenylpyrylium salts exhibiting dual fluorescence has been investigated by fluorescence up-conversion in conjunction with quantum chemical calculations. The short-wavelength emission is due to an excited state localized on the pyrylium fragment and the long-wavelength emission arises from a charge-transfer state delocalized over the whole molecule. The two fluorescing states do not exhibit a precursor−successor relationship. The rise time of the short-wavelength fluorescence is smaller than 200 fs, and that of the long-wavelength emission depends on the electron-donating property of the styryl group substituent. The rise is almost prompt with the weaker donors but is slower, wavelength and viscosity dependent with the strongest electron-donating group. A model involving a S₂/S₁ conical intersection is proposed to account for these observations.

Femtosecond and nanosecond laser flash photolysis was used to determine the photophysical and photochemical processes in aqueous solutions of Fe(III) ion and 5-sulfosalicylic acid (SSA) containing the FeSSA complex and the free ligand. Excitation of the FeSSA complex in the charge transfer band (λ_max = 505 nm) is followed by an ultrafast relaxation to the ground electronic state with two characteristic times of 0.26 and 1.8 ps. The shorter time constant is ascribed to internal conversion to the vibrationally hot electronic ground state of FeSSA and the 1.8 ps time constant is assigned to the vibrational cooling of the ground state. The UV irradiation of the solution (308 nm) leads to the excitation of both the free ligand and the FeSSA complex. The latter relaxes rapidly and the free ligand undergoes intersystem crossing to the triplet state. This system undergoes an irreversible photochemical reaction originating from an electron transfer (k = (9 ± 2) × 10⁸ M⁻¹ s⁻¹) from the free ligand in the triplet state to the FeSSA complex. This electron transfer is accompanied by an energy transfer between these species (k = (1.3 ± 0.2) × 10⁹ M⁻¹ s⁻¹).

The ligand-field induced splitting energies of f-levels in lanthanide-containing elpasolites are derived using the first-principles universal orbital-free embedding formalism [Wesolowski and Warshel, J. Phys. Chem. 1993, 97, 8050]. In our previous work concerning chloroelpasolite lattice (Cs₂NaLnCl₆), embedded orbitals and their energies were obtained using an additional assumption concerning the localization of embedded orbitals on preselected atoms leading to rather good ligand-field parameters. In this work, the validity of the localization assumption is examined by lifting it. In variational calculations, each component of the total electron density (this of the cation and that of the ligands) spreads over the whole system. It is found that the corresponding electron densities remain localized around the cation and the ligands, respectively. The calculated splitting energies of f-orbitals in chloroelpasolites are not affected noticeably in the whole lanthanide series. The same computational procedure is used also for other elpasolite lattices (Cs₂NaLnX₆, where X=F, Br, and I)—materials which have not been fabricated or for which the ligand-field splitting parameters are not available.

Rigid p-octiphenyl rods were used to create helical tetrameric π-stacks of blue, red-fluorescent naphthalene diimides that can span lipid bilayer membranes. In lipid vesicles containing quinone as electron acceptors and surrounded by ethylenediaminetetraacetic acid as hole acceptors, transmembrane proton gradients arose through quinone reduction upon excitation with visible light. Quantitative ultrafast and relatively long-lived charge separation was confirmed as the origin of photosynthetic activity by femtosecond fluorescence and transient absorption spectroscopy. Supramolecular self-organization was essential in that photoactivity was lost upon rod shortening (from p-octiphenyl to biphenyl) and chromophore expansion (from naphthalene diimide to perylene diimide). Ligand intercalation transformed the photoactive scaffolds into ion channels.

The idea of describing a many-electron system using only its electron density, i.e. without constructing its wavefunction, was initiated in the works of Thomas and Fermi. Hohenberg-Kohn theorems of modern density functional theory transformed this idea into an exact theory. The Kohn-Sham formalism, widely used in computer simulations of polyatomic systems today, is based on these theorems but is not orbital-free. It reintroduces orbitals to minimize errors in approximating the total energy. The present review concerns an alternative formalism based also on Hohenberg-Kohn theorems, in which orthogonal orbitals are used not for the whole system but only for subsystems [Cortona, Phys. Rev. B, 44 (1991) 8454]. These orbitals are derived from Kohn-Sham-like one-electron equations, called here Kohn-Sham Equations with Constrained Electron Density (KSCED), in which all terms representing the interactions between the subsystems are expressed as universal functionals of electron density. This formulation provides the formal basis for the orbital-free embedding in first-principles based multi-level simulations of complex systems, in which the orbital-level is retained for a selected subsystem, whereas its environment is described at the orbital-free level [Wesolowski and Warshel, J. Phys. Chem., 97 (1993) 8050]. The formal aspects, development and testing of relevant approximate density functionals, and the possible use of the orbital-free embedding in multi-level modelling are covered in detail in this review. Examples of applications, especially those concerning the electronic structure of embedded systems in the condensed phase are provided.

Multiconfigurational quantum chemical methods show that a quintuple bond is present between the two Cr^I units in the model complex [PhCrCrPh]. The Cr—Cr (1.75 Å) and Cr—Ph (2.02 Å) bonds are shorter than those in the recently reported compound [Ar'CrCrAr'] (Ar'=2,6-(2,6-iPr₂C₆H₃)₂C₆H₃; 1.83 and 2.15 Å, respectively). This difference is attributed to the additional Cr—Ar' interactions.

Nanosecond laser flash photolysis, absorption and fluorescent spectroscopy were used to study the influence of pH on the photophysical and photochemical processes of 5-sulfosalicylic acid (SSA) in aqueous solutions. Information on the excited singlet state intramolecular proton transfer (ESIPT) of the SSA ions could be deduced from the dependence of the quantum yield and the spectral maximum of SSA fluorescence on the pH of the medium. The main photochemical active form of SSA at pH < 10 is the dianion (HSSA²⁻). Excitation of this species gives rise to the HSSA²⁻ triplet state, to the SSA_•²⁻ radical anion and to the hydrated electron. In a neutral medium, the main decay channels of these intermediates are T–T annihilation, recombination and capture by the HSSA²⁻ dianion, respectively. A decrease of pH leads to an increase of the second-order rate constants of disappearance of both HSSA²⁻ triplet state and SSA_•²⁻ radical anion due to their protonation.

Experimental (IR and Raman) and theoretical (Kohn-Sham calculations) methods are used in a combined analysis aimed at refining the available structural data concerning the molecular guests in channels formed by stacked dibenzo-18-crown-6 (DB18C6) crown ether. The calculations are performed for a simplified model comprising isolated DB18C6 unit and its complexes with either H₂O or H₃O⁺ guests, which are the simplest model ingredients of a one-dimensional diluted acid chain, to get structural and energetic data concerning the formation of the complex and to assign the characteristic spectroscopic bands. The oxygen centers in the previously reported crystallographic structure are assigned to either H₂O or protonated species.

The ultrafast ground state recovery (GSR) dynamics of the radical cation of perylene, Pe^•+, generated upon bimolecular photoinduced electron transfer in acetonitrile, has been investigated using pump−pump−probe spectroscopy. With 1,4-dicyanobenzene as electron acceptor, the free ion yield is substantial and the GSR dynamics of Pe^•+ was found to depend on the time delay between the first and second pump pulses, Δt₁₂, i.e., on the “age” of the ion. At short Δt₁₂, the GSR dynamics is biphasic, and at Δt₁₂ larger than about500 ps, it becomes exponential with a time constant around 3 ps. With trans-1,2-dicyanoethylene as acceptor, the free ion yield is essentially zero and the GSR dynamics of Pe^•+ remains biphasic independently of Δt₁₂. The change of dynamics observed with 1,4-dicyanobenzene is ascribed to the transition from paired to free solvated ion, because in the pair, the excited ion has an additional decay channel to the ground state, i.e., charge recombination followed by charge separation. The rate constants deduced from the analysis of these GSR dynamics are all fully consistent with this hypothesis.

The excited-state dynamics of the DNA bisintercalator YOYO-1 and of two derivatives has been investigated using ultrafast fluorescence up-conversion and time-correlated single photon counting. The free dyes in water exist in two forms: nonaggregated dyes and intramolecular H-type aggregates, the latter form being only very weakly fluorescent because of excitonic interaction. The excited-state dynamics of the nonaggregated dyes is dominated by a nonradiative decay with a time constant of the order of 5 ps associated with large amplitude motion around the monomethine bridge of the cyanine chromophores. The strong fluorescence enhancement observed upon binding of the dyes to DNA is due to both the inhibition of this nonradiative deactivation of the nonaggregated dyes and the dissociation of the aggregates and thus to the disruption of the excitonic interaction. However, the interaction between the two chromophoric moieties in DNA is sufficient to enable ultrafast hopping of the excitation energy as revealed by the decay of the fluorescence anisotropy. Finally, these dyes act as solvation probes since a dynamic fluorescence Stokes shift was observed both in bulk water and in DNA. Very similar time scales were found in bulk water and in DNA.

The photophysical properties of the ferric catecholate spin-crossover compounds [(TPA)Fe(R-Cat)]X (TPA=tris(2-pyridylmethyl)amine; X=PF₆^-, BPh₄^-; R-Cat=catecholate dianion substituted by R=NO₂, Cl, or H) are investigated in the solid state. The catecholate-to-iron(III) charge-transfer bands are sensitive both to the spin state of the metal ion and the charge-transfer interactions associated with the different catecholate substituents. Vibronic progressions are identified in the near-infrared (NIR) absorption of the low-spin species. Evidence for a low-temperature photoexcitation process is provided. The relaxation dynamics between 10 and 100 K indicate a pure tunneling process below ≈40 K, and a thermally activated region at higher temperatures. The relaxation rate constants in the tunneling regime at low temperature, k_HL(T→0), vary in the range from 0.58 to 8.84 s^-1. These values are in qualitative agreement with the inverse energy-gap law and with structural parameters. A comparison with ferrous spin-crossover complexes shows that the high-spin to low-spin relaxation is generally faster for ferric complexes, owing to the smaller bond length changes for the latter. However, in the present case the corresponding rate constants are smaller than expected based on the single configurational coordinate model. This is attributed to the combined influence of the electronic configuration and the molecular geometry.

The high-spin → low-spin relaxation in spin-crossover compounds can be described as non-adiabatic multi-phonon process in the strong coupling limit, in which the low-temperature tunnelling rate increases exponentially with the zero-point energy difference between the two states. Based on the hypothesis that the experimental bond length difference between the high-spin and the low-spin state of ~0.2 Å is also valid for low-spin iron(II) complexes, extrapolation of the single configurational coordinate model allows an estimate of the zero-point energy difference for low-spin complexes from kinetic data. DFT calculations on low-spin [Fe(bpy)₃]²⁺ support the structural assumption. However, for low-spin [Fe(terpy)₂]²⁺ the relaxation rate constant shows an anomalous behaviour in so far as it is more in line with spin-crossover systems. This is attributed to very anisotropic bond length changes associated with the spin state change, and the subsequent breakdown of the single mode model.

A planar π-conjugated heteroaromatic molecule 1 has been synthesized and fully characterized; it combines two characteristics, a charge-transfer transition originating from its inherent donor–acceptor nature in its neutral state and an intervalence charge-transfer transition in its 1²⁺ mixed-valence state.

The dynamic Stokes shift of coumarin 153 has been measured in two room-temperature ionic liquids, 1-(3-cyanopropyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-propyl-3-methylimidazolium tetrafluoroborate, using the fluorescence up-conversion technique with a 230 fs instrumental response function. A component of about 10−15% of the total solvation shift is found to take place on an ultrafast time scale < 10 ps. The amplitude of this component is substantially less than assumed previously by other authors. The origin of the difference in findings could be partly due to chromophore-internal conformational changes on the ultrafast time scale, superimposed to solvation-relaxation, or due to conformational changes of the chromophore ground state in polar and apolar environments. First three-pulse photon-echo peak-shift experiments on indocyanine green in room-temperature ionic liquids and in ethanol indicate a difference in the inertial component of the early solvent relaxation of <100 fs.

Computer simulation methods using orbital level of description only for a selected part of the larger systems are prone to the artificial charge leak to the parts which are described without orbitals. The absence of orbitals in one of the subsystems makes it impossible to impose explicitly the orthogonality condition. Using the subsystem formulation of density functional theory, it is shown that the absence of explicit condition of orthogonality between orbitals belonging to different subsystems, does not cause any breakdown of this type of description for the chosen intermolecular complexes (F⁻H₂O and Li⁺H₂O), for which a significant charge-leak problem could be a priori expected.

Matrix isolation infrared (IR) studies have been carried out on the vaporisation of the alkali-metal azides MN₃ (M = Na, K, Rb and Cs). The results show that under high vacuum conditions, molecular KN₃, RbN₃ and CsN₃ are present as stable high-temperature vapour species, together with variable amounts of nitrogen gas and the corresponding metal atoms. The characterisation of these molecular azides is supported by ab initio molecular orbital calculations and density functional theory (DFT) calculations, and for CsN₃ in particular, by the detection of the isotopomers Cs(¹⁴N¹⁵N¹⁴N) and Cs(¹⁵N¹⁴N¹⁴N). The IR spectra are assigned to a "side-on" (C_2v) structure by comparison with the spectral features predicted both by vibrational analysis and calculation. The most intense IR features for KN₃, RbN₃ and CsN₃ isolated in nitrogen matrices lie at 2005, 2004.4 and 2002.2 cm^-1, respectively, and correspond to the N₃ asymmetric stretch. The N₃ bending mode in CsN₃ is identified at 629 cm^-1. An additional feature routinely observed in these experiments occurred at approximately 2323 cm^-1 and is assigned to molecular N₂, perturbed by the close proximity of an alkali-metal atom. The position of this band appeared to show very little cation dependence, but its intensity correlated with the extent of sample thermal decomposition.

Several controversial questions in the field of bimolecular photoinduced electron transfer reactions in polar solvents are first briefly reviewed. Results obtained in our group using ultrafast spectroscopy and giving a new insight into these problems will then be described. They concern the driving force dependence of the charge separation distance, the formation of the reaction product in an electronic excited state, the absence of normal region for weakly exergonic charge recombination processes and the excitation wavelength dependence of the CR dynamics of donor–acceptor complexes.

The oxidative half-reaction of oxygen atom transfer from nitrate to an Mo^IV complex has been investigated at various levels of theory. Two models have been used to simulate the enzyme active site. In the second, more advanced model, additional amino acid residues capable of significantly affecting the catalytic efficiency of the enzyme were included. B3LYP/6-31+G*, ONIOM, and orbital-free embedding approaches have been used to construct the potential energy profile and to qualitatively compare the results of a QM/MM study with those obtained by a full quantum mechanical strategy. The study has confirmed the utility of the orbital-free embedding method in the description of enzymatic processes.

Accurately describing the relative energetics of alternative bis(μ-oxo) and μ-η²:η² peroxo isomers of Cu₂O₂ cores supported by 0, 2, 4, and 6 ammonia ligands is remarkably challenging for a wide variety of theoretical models, primarily owing to the difficulty of maintaining a balanced description of rapidly changing dynamical and nondynamical electron correlation effects and a varying degree of biradical character along the isomerization coordinate. The completely renormalized coupled-cluster level of theory including triple excitations and extremely efficient pure density functional levels of theory quantitatively agree with one another and also agree qualitatively with experimental results for Cu₂O₂ cores supported by analogous but larger ligands. Standard coupled-cluster methods, such as CCSD(T), are in most cases considerably less accurate and exhibit poor convergence in predicted relative energies. Hybrid density functionals significantly underestimate the stability of the bis(μ-oxo) form, with the magnitude of the error being directly proportional to the percentage Hartree−Fock exchange in the functional. Single-root CASPT2 multireference second-order perturbation theory, by contrast, significantly overestimates the stability of bis(μ-oxo) isomers. Implications of these results for modeling the mechanism of C−H bond activation by supported Cu₂O₂ cores, like that found in the active site of oxytyrosinase, are discussed.

Results from quantum chemical calculations that predict the existence of a series of diuranium molecules are reported. Two diuranium chlorides, U₂Cl₆ and U₂Cl₈^2-, and three different carboxylates, U₂(OCHO)₄, U₂(OCHO)₆, and U₂(OCHO)₄Cl₂ have been studied. All species have been found to be stable with a multiply bonded U₂ unit.

Cyclic voltammetry and EPR spectroscopy show that cationic phospholium groups are good electron acceptors whose reduction leads to a neutral radical where the unpaired electron is mainly delocalized on the carbon atoms of the five-membered ring. DFT calculations together with the crystal structure of phospholiums indicate that the electron addition causes a drastic diminution of the exocyclic CPC angle. The SOMO of reduced phospholium is compared to the SOMO of the phosphole radical anion.

The local structure and optical and vibrational properties associated with Mn²⁺-doped cubic AMF₃ (A = K, Rb; M = Mg, Zn, Cd) fluoroperovskites are studied by means of embedding calculations using Kohn–Sham equations with constrained electron density. It is shown that while an electronic parameter like 10Dq essentially depends on the Mn²⁺–F⁻ distance, the local vibration frequencies ω_i (i = a_1g, e_g modes) are dominated by the interaction between F⁻ ligands and nearest M²⁺ ions lying along bonding directions. The high ω_a values observed for KMgF₃:Mn²⁺ and KZnF₃:Mn²⁺, the huge variations of ω_e and ω_a frequencies when the host lattice is changed, as well as the increase of Huang–Rhys factors and the Stokes shift following the host lattice parameter, are shown to be related to this elastic coupling of the MnF₆⁴⁻ complex to the rest of the host lattice. The present results support the conclusion that the Stokes shift is determined by the interaction of the excited ⁴T_1g state with a_1g and e_g local modes while the coupling with the t_2g shear mode is not relevant. The variations of local vibrational frequencies and the Stokes shift induced by a hydrostatic pressure on a given system are shown to be rather different to those produced by the chemical pressure associated with distinct host lattices.

In supramolecular systems, the interaction between different units modulates their photophysical properties. a) For platinum(II) complexes with ligands that have extended π systems, π-stacking and direct metal-metal interactions result in the formation of excimers with characteristically red-shifted luminescence. Time-resolved emission spectra show clear evidence of dual luminescence. b) In phthalocyanines to which electron-donating tetrathiafulvalene (TTF) groups have been fused, the luminescence is strongly quenched by intramolecular electron transfer. The luminescence can be switched on by oxidation of the TTF groups. c) The luminescence of ruthenium tris-bipyridyl derivatives is strongly influenced by the environment. Linked to biotin, the luminescence quantum yield of such a complex is enhanced by 30 % upon binding to avidin. Furthermore, the binding to avidin induces a circular-dichroism signal from the π-π* transition of the initially racemic ruthenium tris-bipyridyl derivative.

The formalism based on the total energy bifunctional (E[ρ_I,ρ_II]) is used to derive interaction energies for several hydrogen-bonded complexes (water dimer, HCN–HF, H₂CO–H₂O, and MeOH–H₂O). Benchmark ab initio data taken from the literature were used as a reference in the assessment of the performance of gradient-free [local density approximation (LDA)] and gradient-dependent [generalized gradient approximation (GGA)] approximations to the exchange-correlation and nonadditive kinetic-energy components of E[ρ_I,ρ_II]. On average, LDA performs better than GGA. The average absolute error of calculated LDA interaction energies amounts to 1.0 kJ/mol. For H₂CO–H₂O and H₂O–H₂O complexes, the potential-energy curves corresponding to the stretching of the intermolecular distance are also calculated. The positions of the minima are in a good agreement (less than 0.2 Å) with the reference ab initio data. Both variational and nonvariational calculations are performed to assess the energetic effects associated with complexation-induced deformations of molecular electron densities.

We report the synthesis, crystal structure and electrochemical behaviour of a complex in which the Ph group of the phosphaalkene PhC(H)=PMes* (Mes*: 2,4,6-tri-tert-butylphenyl) is coordinated to a chromium tricarbonyl group. The EPR spectra resulting from electrochemical and chemical reductions are described and the experimental g and hyperfine tensors (³¹P)T, as determined from the EPR data, are compared with those predicted by DFT calculations for the radical anion (Cr(CO)₃, PhC(H)=PMes)^·−. The structural changes caused by the addition of an electron to the neutral complex are described, together with an estimation of the contribution of Cr(CO)₃ to the stabilization of the radical anion.

Tetrakis(trimethylsiloxy)titanium (TTMST, Ti(OSiMe₃)₄) possesses an isolated Ti center and is a highly active homogeneous catalyst in epoxidation of various olefins. The structure of TTMST resembles that of the active sites in some heterogeneous Ti−Si epoxidation catalysts, especially silylated titania−silica mixed oxides. Water cleaves the Ti−O−Si bond and deactivates the catalyst. An alkyl hydroperoxide, TBHP (tert-butyl hydroperoxide), does not cleave the Ti−O−Si bond, but interacts via weak hydrogen-bonding as supported by NMR, DOSY, IR, and computational studies. ATR−IR spectroscopy combined with computational investigations shows that more than one, that is, up to four, TBHP can undergo hydrogen-bonding with TTMST, leading to the activation of the O−O bond of TBHP. The greater the number of TBHP molecules that form hydrogen bonds to TTMST, the more electrophilic the O−O bond becomes, and the more active the complex is for epoxidation. An allylic alcohol, 2-cyclohexen-1-ol, does not interact strongly with TTMST, but the interaction is prominent when it interacts with the TTMST−TBHP complex. On the basis of the experimental and theoretical findings, a hydrogen-bond-assisted epoxidation mechanism of TTMST is suggested.

In situ attenuated total reflection (ATR) infrared and UV–vis spectroscopy are combined to yield simultaneous time-resolved information on dissolved reaction products, adsorbed species, and the catalyst during the oxidation of ethanol and 2-propanol on a 5% Pd/Al₂O₃ catalyst. The oxidation is initiated by change from hydrogen- to oxygen-saturated solvent flow. 2-Propanol oxidation is observed only in the transient period, whereas ethanol oxidation is also observed in the steady state. This may be ascribed to overoxidation of the catalyst in the former case. In a mixture of the two alcohols the same thing is observed. Competitive adsorption in the steady state may explain this behavior. For ethanol oxidation ethyl acetate is also observed during the transient period. The UV–vis spectra reveal a fast reversible change of the catalyst with switching between hydrogen and oxygen and a slow irreversible change during ethanol oxidation. The latter is ascribed to the change in Pd particle structure, which hardly affects, however, catalyst activity on the time scale of about 1 h.

Adsorption of the tripeptide l-glutathione (γ-glu-cys-gly) on gold surfaces was investigated by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and attenuated total reflection (ATR) infrared spectroscopy. PM-IRRAS was used to study ex situ the adsorbate layer prepared from aqueous solutions at different pH, whereas ATR-IR was applied to study in situ adsorption from ethanol in the presence and absence of acid and base. ATR-IR was furthermore combined with modulation spectroscopy in order to investigate the reversible changes within the adsorbate layer induced by acid and base stimuli, respectively. The molecule is firmly anchored on the gold surface via the thiol group of the cys part. However, the ATR-IR spectra in ethanol indicate a further interaction with the gold surface via the carboxylic acid group of the gly part of the molecule, which deprotonates upon adsorption. Hydrochloric acid readily protonates the two acid groups of the adsorbed molecule. During subsequent ethanol flow the acid groups deprotonate again, a process which proceeds in two distinct steps: a fast step associated with the deprotonation of the acid in the glu part of the molecule and a considerably slower step associated with deprotonation of the acid in the gly moiety. The latter process is assisted by the interaction of the corresponding acid group with the surface. The spectra furthermore indicate a rearrangement of the hydrogen bonding network within the adsorbate layer upon deprotonation. Depending on the protonation state during adsorption of l-glutathione, the response toward identical protonation−deprotonation stimuli is significantly different. This is explained by the ionic state-dependent shape of the molecule, as supported by density functional theory calculations. The different shapes of the individual molecules during layer formation thus influence the structure of the adsorbate layer.

The scope of the asymmetric hydrogenation of functionalized ketones over cinchona-modified platinum was extended to achiral α-hydroxyketones. Cinchonidine showed by far the best catalytic performance affording an enantiomeric excess between 57 and 82% depending on the substrate. O-methoxy-cinchonidine showed poor enantioselection. O-phenoxy-cinchonidine favoured the opposite enantiomer compared to cinchonidine. Solvents with empirical solvent parameters E_T ^N – ranging from 0.10 to 0.65 were tested. Tert-butylmethylether proved to be the most suitable. The highest ratio of substrate/cinchonidine where no loss in e.e. was observed was at around 540, independent of the structure of the α-hydroxyketone. The oxygen in α-position to the ketone seems to play an important role in the enantioselection as well as a phenyl ring or a rigid cis-conformation. The dependence of the enantiomeric excess on the modifier structure and the inversion of the sense of enantiodifferentiation is interpreted in terms of repulsive interactions, which become more evident as the steric demand of the functional group (OH, O-Me, O-Ph) of the modifier increases. The findings indicate that a hydrogen bond in the modifier reactant complex involving the hydroxyl functionality of cinchonidine is not crucial in order to achieve high enantioselectivity.

Alumina-supported rhodium modified with cinchonidine has been investigated with regard to its applicability in the enantioselective hydrogenation of various aromatic ketones possessing an α-hydroxy or α-methoxy group. The study revealed that depending on the substrate, rhodium can outperform the catalytic behavior of platinum. With one of the substrates, 2-hydroxy-1-(4-methoxy-phenyl)-ethanone (4), an enantiomeric excess (ee) of 80% at 89% conversion was reached, which is the highest ee reported so far for chirally modified rhodium. However, completely different conditions are required to achieve optimal catalytic performance with rhodium, compared with platinum. Rhodium requires a much higher modifier concentration, and high hydrogen pressure is favorable. The higher modifier concentration required is traced to the much higher activity of rhodium for the hydrogenation of the quinoline ring, which is assumed to be the anchoring moiety of the cinchona modifiers on the platinum group metals. Changing the modifier from cinchonidine to O-phenoxy-cinchonidine resulted in a switch of the major enantiomer of the product, as exemplified for 2-hydroxyacetophenone (1), which showed a switch from 73% ee in favor of the (R)-product to 68% ee for the (S)-product when the modifier was changed from cinchonidine to O-phenoxy-cinchonidine.

The interaction of proline with self-assembled monolayers (SAMs) of l-glutathione (γ-glu-cys-gly) on gold was investigated by a combination of attenuated total reflection (ATR-IR) infrared and modulation excitation spectroscopy (MES). The latter technique makes use of phase-sensitive detection of periodically varying signals and allows discrimination between species with different kinetics such as dissolved proline and adsorbed molecules. By applying a convection−diffusion model coupled to adsorption and desorption, it was possible to extract relative adsorption and desorption rates from the experimental data for the two enantiomers of proline, fully accounting for mass transport within the flow-through cell. The results show that, in particular, the desorption kinetics is different for the two enantiomers. Therefore, the l-glutathione SAM can discriminate between enantiomers, d-proline being stronger bound. The IR spectra reveal that upon interaction with proline the adsorbed l-glutathione is protonated at the gly part of the molecule, which, in the absence of proline, is bound to the gold surface as carboxylate. The observed protonation of adsorbed l-glutathione upon interaction with proline goes along with a structural change of the former, which seems to play an important role for enantiodiscrimination.

In the hydrogenation of ketopantolactone, the (R,R) and (R,S) diastereomers of a new chiral modifier, pantoyl-naphthylethylamine, afforded 74 and 40% ee, respectively, to (R)-pantolactone. On the basis of NOE studies and theoretical calculations, the different properties of the diastereomers and in particular the effect of acid on the modifier structure are deduced from differences in conformational rigidity and steric constraint. In case of the (R,R)-diastereomer, a loose, extended structure in apolar solvent changes to a compact conformation via an additional intramolecular hydrogen bond, resulting in a more defined “chiral pocket” available for the reactant on the Pt surface.

O-Phenylcinchonidine (PhOCD) is known to efficiently induce inversion of enantioselectivity with respect to cinchonidine (CD) in the enantioselective hydrogenation of various activated ketones on Pt/Al₂O₃. To understand the origin of the switch of enantioselective properties of the catalyst, the adsorption of PhOCD has been studied by in situ ATR-IR spectroscopy, in the presence of organic solvent and dissolved hydrogen, i.e., under conditions used for catalytic hydrogenation. The adsorption structures and energies of the anchoring group of CD and PhOCD were calculated on a Pt 38 cluster, using relativistically corrected density functional theory (DFT). Both approaches indicate that both modifiers are adsorbed via the quinoline ring and that the spatial arrangement of the quinuclidine skeleton is critical for the chiral recognition. New molecular level information on the conformation of CD relative to PhOCD adsorbed on a surface is extracted from the ATR spectra and supported by DFT calculations. The result is a clearer picture of the role played by the phenyl group in defining the chiral space created by the modifiers on Pt. Moreover, when CD was added to a pre-equilibrated adsorbed layer of PhOCD, a chiral adsorbed layer was formed with CD as the dominant modifier, indicating that CD adsorbs more strongly than PhOCD. Conversely, when PhOCD was added to preadsorbed CD, no significant substitution occurred. The process leading to nonlinear effects in heterogeneous asymmetric catalysis has been characterized by in situ spectroscopy, and new insight into a heterogeneous catalytic R−S switch system is provided.

The adsorption of N-acetyl-l-cysteine from ethanol solution on gold has been studied by in situ attenuated total reflection infrared (ATR-IR) spectroscopy, polarization modulation infrared reflection absorption spectroscopy, and a quartz crystal microbalance. After an initial fast adsorption, in situ ATR-IR revealed two considerably slower processes, besides further adsorption. The appearance of carboxylate bands and the partial disappearance of the carboxylic acid bands demonstrated that part of the molecules on the surface underwent deprotonation. In addition, the C=O stretching vibration of the carboxylic acid group shifted to lower and the amide II band to higher wavenumbers, indicating hydrogen-bonding interactions within the adsorbate layer. Based on the initial ATR-IR spectrum, which did not reveal deprotonation, the orientation of the molecule within the adsorbate layer was determined. For this, density functional theory was used to calculate the transition dipole moment vectors of the vibrational modes of N-acetyl-l-cysteine. The projections of the latter onto the z-axis of the fixed surface coordinate system were used to determine relative band intensities for different orientations of the molecule. The analysis revealed that the amide group is tilted with respect to and points away from the surface, whereas the carboxylic acid is in proximity to the surface, which is also supported by a shift of the C−O−H bending mode. This position of the acid group favors its deprotonation assisted by the gold surface and easily enables intermolecular interactions. Periodic acid stimuli revealed reversible protonation/deprotonation of part of the adsorbed molecules. However, only non-hydrogen-bonded carboxylic acid groups showed a response toward the acid stimuli.

To bring evidence for or against the hypothesis of catalytic hydrogenation by intact trinuclear arene ruthenium clusters containing an oxo cap, cationic Ru₃O clusters with three different arene ligands (intrinsically chiral tetrahedra) have been synthesized as racemic mixtures. By introduction of a chiral auxiliary substituent at one of the three different arene ligands, the separation of the two diastereomers was possible. The chiral Ru₃O framework was evidenced by X-ray crystallography, by circular dichroism in the UV and IR regions, and by chiral shift reagents in the NMR spectra. The catalytic hydrogenation of the prochiral substrate methyl 2-acetamidoacrylate using a chiral Ru₃O cluster showed no asymmetric induction, suggesting that the catalytically active species is not the intact Ru₃O cluster.

Vibrational circular dichroism is used to determine the conformation of a thiol adsorbed on gold nanoparticles.

The molecular structure of the highly oxygen-sensitive complex [L³Cu^I(NCCH₃)](BF₄) (1) reveals approximately symmetrical coordination by the fac-tridentate (tripodal) ligand L³ = tris(3-isopropyl-4,5-trimethylenepyrazolyl)methane and a rather short Cu^I-N(acetonitrile) distance of 1.865(5) Å. In CH₂Cl₂ at -78 °C the colourless compound reacts with O₂ to yield a labile purple intermediate (λ_max 517 nm) - presumably a peroxodicopper(II) complex - which decomposes at -30 °C. No such intermediate was observed on reaction of the Cu^I complex of bis(2-pyridylmethyl)benzylamine with O₂ at -80 °C. However, an EPR spectrum with g^|| = 2.17 and g^_|_ = 2.03 without ^63,65Cu hyperfine splitting was observed at low temperatures. Exposure of the precursor 1 to air under ambient conditions yields dinuclear [L³Cu^||(μ-OH)₂Cu^IIL³](BF₄)₂ (2) which exhibits an EPR detectable dissociation into monomers in CH₂Cl₂ solution. The structure of the hexakis(dichloromethane) solvate of 2 with Cu-Cu and Cu-O distances of 3.055 and 1.94Å, respectively, is typical for dihydroxo-bridged dicopper compounds with square-pyramidal Cu^|| configuration (τ = 0.03), adopting an anti arrangement. In agreement with the relatively wide Cu-O-Cu angles of 103.5° an analysis of the temperature dependence of the magnetic susceptibility revealed a rather strong (J = -633 cm^-1) antiparallel spin-spin coupling. The effect is ascribed to the steric bulk of the ligand L³.

Herein is reported an experimental and theoretical study of the circular dichroism properties of TRISPHAT (1) anion. ECD analysis of the [tetramethylammonium][Δ-1] salt confirms the absolute configuration assignment obtained through X-ray crystallographic analysis of the parent cinchonidium salt. The structure, infrared, and vibrational circular dichroism (VCD) spectra derived from density functional theory (DFT) calculations are compared with experimental data.

The enantioseparation of baclofen (4-amino-3-p-chlorophenylbutyric acid) was achieved by CE-LIF with highly sulfated β-CD (HS-β-CD) as chiral selector. Naphthalene-2,3-dicarboxaldehyde was used for the derivatization of nonfluorescent baclofen. HS-β-CD (2%) containing 50 mM borate buffer at pH 9.5 was chosen as the optimal running electrolyte and applied to the analysis of baclofen enantiomers in human plasma. The linearity of calibration curves (R ² ≥ 0.998) for R-(-) and S-(+)-baclofen was in the 0.1-2.0 μM concentration range. After a simple ACN-protein precipitation, the LOD of baclofen in plasma sample was found as low as 50 nM.

The optical properties of a thin film of the [Ru(bpy)₃][NaCr(ox)₃] network structure obtained by pulsed laser deposition are described. The luminescence shows the characteristic doublet of R lines at 14 400 cm⁻¹ of the spin-forbidden ligand field transition ^2E(t2g3)→^4A₂(t2g3) of the [Cr(ox)₃]³⁻ chromophore. The resonant energy migration within the R₁ line shows that the three-dimensional crystallographic structure is preserved during the coating process. The observation of the R lines of [Cr(bpy)₃]³⁺ at 13 710 cm⁻¹ indicates that a small fraction of Cr³⁺ ions migrate from the oxalate network to the tris-bipyridine cation site in the cavities of the network.

In many instances, the deduction of spectroscopic parameters from electron paramagnetic resonance spectra depends on spectrum simulation and parameter optimization. We have developed two software packages based on the approximate formulae of Iwasaki for the calculation of line positions and on the Levenberg-Marquardt algorithm for nonlinear least-squares optimization. Our software applies to systems having an anisotropicg-tensor and an arbitrary number of hyperfine interactions with nuclei. They are written in the FORTRAN 77 programming language. At present, neither the nuclear quadrupolar interaction nor the nuclear Zeeman interaction terms are handled. The programs CRISAJU and EPRPOWDERFIT apply to the cases of single crystals and powders, respectively. For use in the latter, thanks to the software ODYSSEE which implements automatic differentiation of algorithms, an ancillary subroutine, which contributes to the performance of the optimization, was created automatically.

The recombination dynamics of ion pairs generated upon electron transfer quenching of perylene in the first singlet excited state by tetracyanoethylene in acetonitrile is quantitatively described by the extended unified theory of photoionization/recombination. The extension incorporates the hot recombination of the ion pair passing through the level-crossing point during its diffusive motion along the reaction coordinate down to the equilibrium state. The ultrafast hot recombination vastly reduces the yield of equilibrated ion pairs subjected to subsequent thermal charge recombination and separation into free ions. The relatively successful fit of the theory to the experimentally measured kinetics of ion accumulation/recombination and free ion yield represents a firm justification of hot recombination of about 90% of primary generated ion pairs.

UNIL088 is a water-soluble prodrug of cyclosporine A (CsA) developed for topical eye delivery. Such a prodrug has to fulfil two paradoxical requirements as it must be rapidly hydrolysed under physiological conditions but also retain a long shelf-life in aqueous media. This study has been conducted to explore the stability of UNIL088 formulated as an eyedrop solution. The stability study of the prodrug was performed over a pH range of 5–7 at 20 °C and at various ionic strengths. The molecule was more stable at pH 5 than at pH 7 with conversion rate constant of 3.2 × 10⁻³ and 26.0 × 10⁻³ days⁻¹, respectively. The effect of temperature was studied at four different temperatures and activation energy was determined. Conversion of UNIL088 followed a pseudo-first-order kinetic with an activation energy of 79.4 kJ mol⁻¹. Due to its low solubility, CsA generated precipitated in the solution. The average size of CsA precipitates, determined by photon spectroscopy, was 0.22 and 1.08 μm at 7 and 14 days, respectively. The hydrolysis mechanism was partially elucidated by identification of the intermediate pSer-Sar-CsA.

The tendency for mixed-isotope O₂ fragments to exhibit different stretching frequencies in asymmetric environments is examined with various levels of electronic structure theory for simple peroxides and peroxyl radicals, as well as for a variety of monocopper–O₂ complexes. The study of the monocopper species is motivated by their relevance to the active site of galactose oxidase. Extensive theoretical work with an experimental model characterized by Jazdzewski et al. (J. Biol. Inorg. Chem. 8:381–393, 2003) suggests that the failure to observe a splitting between ¹⁶O¹⁸O and ¹⁸O¹⁶O isotopomers cannot be taken as evidence against end-on O₂ coordination. Conformational analysis on an energetic basis, however, is complicated by biradical character inherent in all of the copper–O₂ singlet structures.

Quantum chemical calculations show that metal−hydride molecules are more compact when they are placed inside a fullerene cage than when they are isolated molecules. The metal−hydrogen bond distance in ZrH₄ becomes 0.15 Å shorter when it is placed inside a C₆₀ cage. Metal−polyhydride molecules with a large number of H atoms such as ScH₁₅ and ZrH₁₆, which are not bound as isolated molecules, are predicted to be bound inside a fullerene cage. It is also shown that two TiH₁₆ clusters are bound inside a bicapped (9,0) carbon nanotube. Possible ways to make metal−hydrides inside C₆₀ and nanotubes are suggested.

Four compounds containing metal−metal quadruple bonds, the [M₂(CH₃)₈]^n- ions (M = Cr, Mo, W, Re and n = 4, 4, 4, 2, respectively), have been studied theoretically using multiconfigurational quantum-chemical methods. The molecular structure of the ground state of these compounds has been determined and the energy of the δ → δ* transition has been calculated and compared with previous experimental measurements. The high negative charges on the Cr, Mo, and W complexes lead to difficulties in the successful modeling of the ground-state structures, a problem that has been addressed by the explicit inclusion of four Li⁺ ions in these calculations. The ground-state geometries of the complexes and the δ → δ* transition have been modeled with either excellent agreement with experiment (Re) or satisfactory agreement (Cr, Mo, and W).

The synthesis, structural characterization, and photophysical behavior of a 14-membered tetraazamacrocycle with pendant 4-dimethylaminobenzyl (DMAB) and 9-anthracenylmethyl groups is reported (L³, 6-((9-anthracenylmethyl)amino)-trans-6,13-dimethyl-13-((4-dimethylaminobenzyl)amino)-1,4,8,11-tetraazacyclotetradecane). In its free base form, this compound displays rapid intramolecular photoinduced electron transfer (PET) quenching of the anthracene emission, with both the secondary amines and the DMAB group capable of acting as electron donors. When complexed with Zn(II), the characteristic fluorescence of the anthracene chromophore is restored as the former of these pathways is deactivated by coordination. Importantly, it is shown that the DMAB group, which remains uncoordinated and PET active, acts only very weakly to quench emission, by comparison to the behavior of a model Zn complex lacking the pendant DMAB group, [ZnL²]²⁺ (Chart 1). By contrast, Stern−Volmer analysis of intermolecular quenching of [ZnL²]²⁺ by N,N-dimethylaniline (DMA) has shown that this reaction is diffusion limited. Hence, the pivotal role of the bridge in influencing intramolecular PET is highlighted.

Mixed matlokite hosts of composition BaFBr_xI_1−x(0≤x≤1) (pure and doped with Sm²⁺, Eu²⁺) were studied with x-ray crystallography, luminescence, Raman, and electron paramagnetic resonance (EPR) spectroscopy. Results are presented for BaFBr_0.5I_0.5 which demonstrate that a ferrielectric domain structure is formed due to the fact that the heavy halogen ions form separate sublattices with randomly distributed domain walls. The space group of a domain is P4  mm (No. 99). The EPR data from Eu²⁺ allowed to determine the volume fraction of domains.

Separation and determination of some common metal ions was achieved with methyl 3-amino-3-(pyridin-3-yl)propanoate dihydrochloride (MAPP) as an ion-pairing reagent and pyridine as a detectable counter-ion for indirect UV detection at 254 nm. The effects of the complexing reagent and chromophore concentrations, applied voltage, and organic solvent content on the separation were investigated. The optimized separation was carried out in a running electrolyte containing 16 mM MAPP and 20 mM pyridine at pH 4.0 and was successfully applied to the qualitative and quantitative analysis of Li⁺, Na⁺, Mg²⁺, Ca²⁺, Ba²⁺, Ni²⁺, and Zn²⁺ in pharmaceutical vitamin preparations and various water samples.

The orbital-free frozen-density embedding scheme within density-functional theory [ T. A. Wesolowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993) ] is applied to the calculation of induced dipole moments of the van der Waals complexes CO₂⋯X (X = He, Ne, Ar, Kr, Xe, Hg). The accuracy of the embedding scheme is investigated by comparing to the results of supermolecule Kohn-Sham density-functional theory calculations. The influence of the basis set and the consequences of using orbital-dependent approximations to the exchange-correlation potential in embedding calculations are examined. It is found that in supermolecular Kohn-Sham density-functional calculations, different common approximations to the exchange-correlation potential are not able to describe the induced dipole moments correctly and the reasons for this failure are analyzed. It is shown that the orbital-free embedding scheme is a useful tool for applying different approximations to the exchange-correlation potential in different subsystems and that a physically guided choice of approximations for the different subsystems improves the calculated dipole moments significantly.