Single crystals of Ce₂RhGa₁₂ have been synthesized using Ga flux and their structure was determined by single-crystal X-ray diffraction. Ce₂RhGa₁₂ crystallizes in the tetragonal space group P4/nbm (No. 125), and is isostructural to Ce₂PdGa₁₂, with Z = 2 and lattice parameters a = 6.0405 Å and c = 15.706 Å. Data were collected at the Swiss Norwegian Beam Line at the European Synchrotron Facility, Grenoble, France. Laue diffraction was carried out to confirm the quality of the single crystal and showed well-defined spots and tetragonal symmetry.

The green-fluorescent protein of the jellyfish operates with the most powerful phenolate donors in the push–pull fluorophore. To nevertheless achieve red fluorescence with the same architecture, sea anemone and corals apply oxidative imination, a process that accounts for the chemistry of vision as well. The objective of this study was to apply these lessons from nature to one of the most compact family of panchromatic fluorophores, i.e. core-substituted naphthalenediimides (cNDIs). We report straightforward synthetic access to hydroxylated cNDI and cPDI cores by palladium-catalyzed cleavage of allyloxy substituents. With hydroxylated cNDIs but not cPDIs in water-containing media, excited-state intramolecular proton transfer yields a second bathochromic emission. Deprotonation of hydroquinone, catechol and boronic ester cores provides access to an impressive panchromism up to the NIR frontier at 640 nm. With cNDIs, oxidative imination gives red shifts up to 638 nm, whereas the expanded cPDIs already absorb at 754 nm upon deprotonation of hydroquinone cores. The practical usefulness of hydroquinone cNDIs is exemplified by ratiometric sensing of the purity of DMF with the “naked eye” at a sensitivity far beyond the “naked nose”. We conclude that the panchromatic hypersensitivity toward the environment of the new cNDIs is ideal for pattern generation in differential sensing arrays.

The title compound, an achiral flexible molecule containing a 1,2,3-triazole structure as the acceptor subunit, crystallizes as a single enantiomorph in the space group P2₁2₁2₁. The material exhibits nonlinear optical properties and is capable of second harmonic generation. Thus, the developed molecular scaffold represents an interesting novel type of NLO chromophore.

Two molecules containing two phenylphosphaalkene moieties linked by an anthracene (1) or by a naphthalene (2) ring have been synthesized and their crystal structures have been determined. While electrochemical measurements show that these two systems are easily reduced, EPR spectra indicate that, at room temperature, the electronic structures of the two reduction compounds 1˙⁻ and 2˙⁻ are quite different. In 1˙⁻, in good accordance with DFT predictions, the unpaired electron is delocalized on the full molecule while in 2˙⁻ it is confined on a single phosphaalkene moiety. This difference is attributed to the short distance between the two phenylphosphaalkene groups in 2˙⁻ which hinders their reorientation after addition of an electron. The role of this motion is consistent with the fact that two additional paramagnetic species are detected at 145 K: the dianion 2²⁻ characterized by a rather small exchange coupling constant and the radical monoanion 2*˙⁻ resulting from the formation of a one electron P–P bond. These two species are probably reaction intermediates which can lead to the formation of biphosphane.

The recently developed mechanoelastic model is applied to characterize the thermal transition in spin-crossover complexes, with special attention given to the case of spin-crossover nanoparticles. In a two-dimensional system, hexagonal-shaped samples with open boundary conditions are composed of individual molecules that are linked by springs and can switch between two states, namely, the high-spin (HS) and the low-spin (LS) states. The switching of an individual molecule during the spin transition is decided by way of a Monte Carlo standard procedure, using transition probabilities depending on the temperature, the energy gap between the two states, the enthalpy difference, the degeneracy ratio, and the local pressure determined by the elongation or compression of its closest springs. The influence of external parameters, such as temperature sweeping rate and pressure, or intrinsic features of the system, such as the value of its spring constant, on the width of the thermal hysteresis, its shape, and its position are discussed. The particular case of spin-crossover nanoparticles is treated by considering them embedded into a polymer environment, which essentially affects the molecules situated at the edges and faces by decreasing their transition probabilities from HS to LS. Finally, the pressure hysteresis, obtained by varying the external pressure at constant temperature is discussed.

An efficient synthetic approach to a symmetrically functionalized tetrathiafulvalene (TTF) derivative with two diamine moieties, 2-[5,6-diamino-4,7-bis(4-pentylphenoxy)-1,3-benzodithiol-2-ylidene]-4,7-bis(4-pentylphenoxy)-1,3-benzodithiole-5,6-diamine (2), is reported. The subsequent Schiff-base reactions of 2 afford large π-conjugated multiple D–A arrays, for example the triad 2-[4,9-bis(4-pentylphenoxy)-1,3-dithiolo[4,5-g]quinoxalin-2-ylidene]-4,9-bis(4-pentylphenoxy)-1,3-dithiolo[4,5-g]quinoxaline (8) and the corresponding tetrabenz[bc,ef,hi,uv]ovalene-fused pentad 1, in good yields and high purity. The novel redox-active nanographene 1 is so far the largest known TTF-functionalized polycyclic aromatic hydrocarbon with a well-resolved ¹H NMR spectrum. The electrochemically highly amphoteric pentad 1 and triad 8 exhibit various electronically excited charge-transfer states in different oxidation states leading to intense optical intramolecular charge transfer (ICT) absorbances over a wide spectral range. The chemical and electrochemical oxidations of 1 result in an unprecedented TTF^•+ radical cation dimerization, leading to the formation of [1^•+]₂ at room temperature in solution due to the stabilizing effect arising from strong π–π interactions. Moreover, ICT fluorescence is observed with large solvent-dependent Stokes shifts and quantum efficiencies of 0.05 for 1 and 0.035 for 8 in CH₂Cl₂.

We model here the behavior of spin transition compounds, considering molecules arranged in a 2D hexagonal lattice and interacting via springs. The role of impurities in the clustering and nucleation phenomena is analyzed, as well as the manner in which the impurities affect the relaxation curves. The switching of the individual molecules is checked using a Monte Carlo procedure. When a molecule changes its state, it also modifies its volume, and the new equilibrium positions of all the molecules are calculated. As in previously reported experiments, it is found here that bigger impurities slow down the relaxation from the metastable high-spin state to the low-spin state, while smaller impurities act in an opposite way. It is shown that if the concentration of the impurities is higher than a certain threshold, then they act as a barrier, trammeling the fast evolution of domains developing from the edges.

PURPOSE. To compare the photochemical properties of UV filter molecules present in the human lens (kynurenine, KN; 3-hy- droxykynurenine, 3OHKN; 3-hydroxykynurenine O-gluco- side, 3OHKG; 4-(2-aminophenyl)-4-oxobutanoic acid, AHA; and glutathionyl-kynurenine, GSH-KN) with the use of the following parameters: excited singlet lifetime, fluorescence quantum yield, triplet quantum yield, photodecomposition quantum yield.

METHODS. The excited singlet lifetimes were measured with the use of fluorescence upconversion (time resolution, 210 fs) and pump-probe transient absorption (time resolution, 200 fs) methods. The fluorescence quantum yields were determined relative to an aqueous solution of quinine bisulfate. The triplet quantum yields were measured with the use of nanosecond laser flash photolysis. The photodecomposition quantum yields were determined by steady state photolysis followed by the high-performance liquid chromatography analysis.

RESULTS. The secondary UV filters—AHA and GSH-KN are better photosensitizers than the primary ones -KN, 3OHKN and 3OHKG: the singlet state lifetimes of the secondary UV filters are longer, and the quantum yields of fluorescence and triplet state formation are higher.

CONCLUSIONS. With aging, the ratio primary/secondary UV filters in the human lens decreases from approximately 10:1 to 2:1. The obtained results demonstrate that the quality of the secondary UV filters is inferior compared to the primary ones, which may result in a higher susceptibility of old lenses to UV light. That might be an important factor for the development of the age-related cataract.

Facile access to complex systems is crucial to generate the functional materials of the future. Herein, we report self-organizing surface-initiated polymerization (SOSIP) as a user-friendly method to create ordered as well as oriented functional systems on transparent oxide surfaces. In SOSIP, self-organization of monomers and ring-opening disulfide exchange polymerization are combined to ensure the controlled growth of the polymer from the surface. This approach provides rapid access to thick films with smooth, reactivatable surfaces and long-range order with few defects and high precision, including panchromatic photosystems with oriented four-component redox gradients. The activity of SOSIP architectures is clearly better than that of disordered controls.

Highly occupied: A highly porous form of Mg(BH₄)₂ (see picture; Mg green, BH₄ blue, unit cells shown in red) reversibly absorbs H₂, N₂, and CH₂Cl₂. At high pressures, this material transforms into an interpenetrated framework that has 79 % higher density than the other polymorphs. Mg(BH₄)₂ can act as a coordination polymer that has many similarities to metal–organic frameworks.

In this article, the synthesis of a novel high-conjugated ligand and its corresponding Ru(II) complex PTFTF:Ru is reported, along with the linear and nonlinear optical characterizations. Two-photon absorption based optical power limiting properties (OPL), especially in the near infrared, are described and compared to those of the analogous complexes previously published. Combined with a preliminary theoretical approach, this allows us to highlight several key parameters for OPL optimization in such molecular systems and more particularly the spectral overlap between TPA and excited-state absorption.

This work illustrates a simple approach for optimizing the lanthanide luminescence in molecular dinuclear lanthanide complexes and identifies a particular multidentate europium complex as the best candidate for further incorporation into polymeric materials. The central phenyl ring in the bis-tridentate model ligands L3–L5, which are substituted with neutral (X = H, L3), electron-withdrawing (X = F, L4), or electron-donating (X = OCH₃, L5) groups, separates the 2,6-bis(benzimidazol-2-yl)pyridine binding units of linear oligomeric multi-tridentate ligand strands that are designed for the complexation of luminescent trivalent lanthanides, Ln(III). Reactions of L3–L5 with [Ln(hfac)₃(diglyme)] (hfac^– is the hexafluoroacetylacetonate anion) produce saturated single-stranded dumbbell-shaped complexes [Ln₂(Lk)(hfac)₆] (k = 3–5), in which the lanthanide ions of the two nine-coordinate neutral [N₃Ln(hfac)₃] units are separated by 12–14 Å. The thermodynamic affinities of [Ln(hfac)₃] for the tridentate binding sites in L3–L5 are average (6.6 ≤ log(β_2,1^Y,Lk) ≤ 8.4) but still result in 15–30% dissociation at millimolar concentrations in acetonitrile. In addition to the empirical solubility trend found in organic solvents (L4 > L3 >> L5), which suggests that the 1,4-difluorophenyl spacer in L4 is preferable, we have developed a novel tool for deciphering the photophysical sensitization processes operating in [Eu₂(Lk)(hfac)₆]. A simple interpretation of the complete set of rate constants characterizing the energy migration mechanisms provides straightforward objective criteria for the selection of [Eu₂(L4)(hfac)₆] as the most promising building block.

Self-assembly processes between a tripodal ligand and Ln^III cations have been investigated by means of supramolecular analytical methods. At an equimolar ratio of components, tetranuclear tetrahedral complexes are readily formed in acetonitrile. The structural analysis of the crystallographic data shows a helical wrapping of binding strands around metallic cations. The properties of this series of highly charged 3D compounds were examined by using NMR spectroscopy and optical methods in solution and in the solid state. In the presence of excess metal, a new trinuclear complex was identified. The X-ray crystal structure elucidated the coordination of metallic cations with two ligands of different conformations. By varying the metal/ligand ratio, a global speciation of this supramolecular system has been evidenced with different spectroscopic methods. In addition, these rather complicated equilibria were successfully characterised with the thermodynamic stability constants. A rational analysis of the self-assembly processes was attempted by using the thermodynamic free energy model and the impact of the ligand structure on the effective concentration is discussed.

The structure and thermodynamic properties of lanthanide complexes with a new tripodal ligand L2 have been elucidated using different physicochemical methods. At stoichiometric ratios, the tetrahedral three-dimensional complexes with lanthanide cations are formed in acetonitrile with good stabilities. Despite minor structural changes comparing to previously investigated tripodal ligands, the resulting assembly exhibits different features revealed with the crystal structure of [Eu₄L2₄](OH)(ClO₄)₁₁ (orthorhombic, Pbcn). Interestingly, the highly charged edifice contains an inner cage encapsulating a perchlorate anion. Such lanthanide mediated cage-like assemblies are rare, and may be of interest for different sensing applications. Indeed, the anionic guest can be exchanged with different anions. The related host–guest equilibria were investigated with NMR techniques. Various aspects of these reactions are qualitatively discussed.

The bi-functional for the non-electrostatic part of the exact embedding potential of frozen-density embedding theory (FDET) depends on whether the embedded part is described by means of a real interacting many-electron system or the reference system of non-interacting electrons (see [Wesolowski, Phys. Rev. A. 77, 11444 (2008)]). The difference δΔF^MD[ρ_A] / δρ_A^(r), where ΔF^MD[ρ_A] is the functional bound from below by the correlation functional E_c[ρ_A] and from above by zero. Taking into account ΔF^MD[ρ_A] in both the embedding potential and in energy is indispensable for assuring that all calculated quantities are self-consistent and that FDET leads to the exact energy and density in the limit of exact functionals. Since not much is known about good approximations for ΔF^MD[ρ_A], we examine numerically the adequacy of neglecting ΔF^MD[ρ_A] entirely. To this end, we analyze the significance of δΔF^MD[ρ_A] / δρ_A^(r) in the case where the magnitude of ΔF^MD[ρ_A] is the largest, i.e., for Hartree-Fock wavefunction. In hydrogen bonded model systems, neglecting δΔF^MD[ρ_A] / δρ^(r) in the embedding potential marginally affects the total energy (less than 5% change in the interaction energy) but results in qualitative changes in the calculated hydrogen-bonding induced shifts of the orbital energies. Based on this estimation, we conclude that neglecting δΔF^MD[ρ_A] / δρ_A^(r) may represent a good approximation for multi-reference variational methods using adequate choice for the active space. Doing the same for single-reference perturbative methods is not recommended. Not only it leads to violation of self-consistency but might result in large effect on orbital energies. It is shown also that the errors in total energy due to neglecting δΔF^MD[ρ_A] / δρ_A^(r) do not cancel but rather add up to the errors due to approximation for the bi-functional of the non-additive kinetic potential.

In embedding methods such as those labeled commonly as QM/MM, the embedding operator is frequently approximated by the electrostatic potential generated by nuclei and electrons in the environment. Such approximation is especially useful in studies of the potential energy surface of embedded species. The effect on energy of neglecting the non-Coulombic component of the embedding operator is corrected a posteriori. The present work investigates applicability of such approximation in evaluation of electronic excitation energy, the accuracy of which depends directly on that of the embedding potential. For several model systems involving cis-7-hydroxiquinoline hydrogen-bonded to small molecules, we demonstrate that such truncation of the embedding operator leads to numerically unstable results upon increasing the size of the atomic basis sets. Approximating the non-Coulombic component of the embedding potential using the expression derived in Frozen-Density Embedding Theory ([Wesolowski and Warshel, J. Phys. Chem.1993, 97, 8050] and subsequent works) by means of even a simple bifunctional dependent on the electron density of the chromophore and its hydrogen-bonded environment, restores the numerical stability of the excitation energies that reach a physically meaningful limit for large basis sets.

A multiconfigurational self-consistent field method based on the concept of generalized active space (GAS) is presented. GAS wave functions are obtained by defining an arbitrary number of active spaces with arbitrary occupation constraints. By a suitable choice of the GAS spaces, numerous ineffective configurations present in a large complete active space (CAS) can be removed, while keeping the important ones in the CI space. As a consequence, the GAS self-consistent field approach retains the accuracy of the CAS self-consistent field (CASSCF) ansatz and, at the same time, can deal with larger active spaces, which would be unaffordable at the CASSCF level. Test calculations on the Gd atom, Gd₂ molecule, and oxoMn(salen) complex are presented. They show that GAS wave functions achieve the same accuracy as CAS wave functions on systems that would be prohibitive at the CAS level.

We present the femtosecond spectroscopic investigation of a covalently linked dyad, PCB-P3HT, formed by a segment of the conjugated polymer P3HT (regioregular poly(3-hexylthiophene)) that is end capped with the fullerene derivative PCB ([6,6]-phenyl-C61-butyric acid ester), adapted from PCBM. The fluorescence of the P3HT segment in tetrahydrofuran (THF) solution is reduced by 64% in the dyad compared to a control compound without attached fullerene (P3HT-OH). Fluorescence upconversion measurements reveal that the partial fluorescence quenching of PCB-P3HT in THF is multiphasic and occurs on an average time scale of 100 ps, in parallel to excited-state relaxation processes. Judging from ultrafast transient absorption experiments, the origin of the quenching is excitation energy transfer from the P3HT donor to the PCB acceptor. Due to the much higher solubility of P3HT compared to PCB in THF, the PCB-P3HT dyad molecules self-assemble into micelles. When pure C60 is added to the solution, it is incorporated into the fullerene-rich center of the micelles. This dramatically increases the solubility of C60 but does not lead to significant additional quenching of the P3HT fluorescence by the C60 contained in the micelles. In PCB-P3HT thin films drop-cast from THF, the micelle structure is conserved. In contrast to solution, quantitative and ultrafast (<150 fs) charge separation occurs in the solid-state films and leads to the formation of long-lived mobile charge carriers with characteristic transient absorption signatures similar to those that have been observed in P3HT:PCBM bulk heterojunction blends. While π -stacking interactions between neighboring P3HT chains are weak in the micelles, they are strong in thin films drop-cast from ortho-dichlorobenzene. Here, PCB-P3HT self-assembles into a network of long fibers, clearly seen in atomic force microscopy images. Ultrafast charge separation occurs also for the fibrous morphology, but the transient absorption experiments show fast loss of part of the charge carriers due to intensity-induced recombination and annihilation processes and monomolecular interfacial trap-mediated or geminate recombination. The yield of the long-lived charge carriers in the highly organized fibers is however comparable to that obtained with annealed P3HT:PCBM blends. PCB-P3HT can therefore be considered as an active material in organic photovoltaic devices.

Even flow: Photoinduced symmetry-breaking charge separation takes place in a few picoseconds in a 1,3-bis(perylene)propane dyad in polar solvents. Polarized transient absorption measurements show that the direction of the charge flow is random and entirely governed by the fluctuations of the solvent orientation around the dyad.

Several novel aromatic ketone-based two-photon initiators containing triple bonds and dialkylamino groups were synthesized and the structure-activity relationships were evaluated. Branched alkyl chains were used at the terminal donor groups to improve the solubility in the multifunctional monomers. Because of the long conjugation length and good coplanarity, the evaluated initiators showed large two-photon cross section values, while their fluorescence lifetimes and quantum yields strongly depend on the solvent polarity. All novel initiators exhibited high activity in terms of two-photon-induced microfabrication. This is especially true for fluorenone-based derivatives, which displayed much broader processing windows than well-known highly active initiators from the literature and commercially available initiators. While the new photoinitiators gave high reactivity in two-photon-induced photopolymerization at concentration as low as 0.1% wt, these compounds are surprisingly stable under one photon condition and nearly no photo initiation activity was found in classical photo DSC experiment.

Barium calcium magnesium fluoride (Ba₂(Ba_xCa_1-x)Mg₄F₁₄, x=0.19-0.26) has been synthesized at 850 °C from precursors prepared by the solution precipitation method. Single crystals with composition of Ba_2.200(2)Ca_0.800(2)Mg₄F₁₄were obtained after prolonged heating. Lattice parameters from single crystal data are a = 12.4203(8) and c = 7.4365(5) Å [tetragonal, space group P4₂/mnm (No. 136)]. They increase with increasing barium concentration within a given stability window. The structure is built of a network of MgF₆ octahedra forming a pyrochlore related channel system and isolated fluorine ions. Within the channels, heavy alkaline earth ions are located. The wide channel is filled with off-center positioned barium ions. The channel with a narrow cross section hosts both ions, Ca²⁺and Ba²⁺. The structure is isotypic with Pb₃Nb₄O₁₂F₂ but has a different coordination around Ba/Ca and Pb, respectively. Doped with ∼1% Eu(II), the compound shows intense blue luminescence under UV activation.

Several assertions which are incorrect or might be misleadingly interpreted as well as omissions of issues concerning the non-additive kinetic energy potential made by Fux et al. are analyzed. They concern issues of great importance for any computational method based on the orbital-free embedding theory: evaluation of the total energy, approximating the non-additive kinetic potential, exact properties of non-additive kinetic energy potential. In a nutshell, the authors do not distinguish between two different quantities: the functional, i.e., the correspondence assigning the non-additive kinetic potential to a pair of electron densities and the function (the potential itself).

The p53 tumour suppressor gene, the most frequently mutated gene in human cancer, encodes a transcription factor that contains sequence-specific DNA binding and homo-tetramerization domains. Interestingly, the affinities of p53 for specific and non-specific DNA sites differ by only one order of magnitude, making it hard to understand how this protein recognizes its specific DNA targets in vivo. We describe here the structure of a p53 polypeptide containing both the DNA binding and oligomerization domains in complex with DNA. The structure reveals that sequence- specific DNA binding proceeds via an induced fit mechan- ism that involves a conformational switch in loop L1 of the p53 DNA binding domain. Analysis of loop L1 mutants demonstrated that the conformational switch allows DNA binding off-rates to be regulated independently of affinities. These results may explain the universal prevalence of conformational switching in sequence-specific DNA binding proteins and suggest that proteins like p53 rely more on differences in binding off-rates, than on differences in affinities, to recognize their specific DNA sites.

The activities of our research group in the field of photoinduced electron transfer reactions are discussed and illustrated by several examples

We theoretically analyze, fabricate, and characterize a three-dimensional plasmonic nanostructure that exhibits a strong and isotropic magnetic response in the visible spectral domain. Using two different bottom-up approaches that rely on self-organization and colloidal nanochemistry, we fabricate clusters consisting of dielectric core spheres, which are smaller than the wavelength of the incident radiation and are decorated by a large number of metallic nanospheres. Hence, despite having a complicated inner geometry, such a core–shell particle is sufficiently small to be perceived as an individual object in the far field. The optical properties of such complex plasmonic core–shell particles are discussed for two different core diameters.

A solid solution of magnesium and manganese borohydrides was studied by in situ synchrotron radiation X-ray powder diffraction and infrared spectroscopy. A combination of thermogravimetry, mass and infrared spectroscopy, and atomic emission spectroscopy were applied to clarify the thermal gas desorption of pure Mn(BH₄)₂ and a solid solution of composition Mg_0.5Mn_0.5(BH₄)₂. Mg_xMn_(1−x)(BH₄)₂ (x = 0–0.8) conserves the trigonal structure of Mn(BH₄)₂ at room temperature. Manganese is dissolved in the hexagonal structure of α-Mg(BH₄)₂, with the upper solubility limit not exceeding 10 mol.% at room temperature. There exists a two-phase region of trigonal and hexagonal borohydrides within the compositional rangex = 0.8–0.9 at room temperature. Infrared spectra show splitting of various vibrational modes, indicating the presence of two cations in the trigonal Mg_xMn_(1−x)(BH₄)₂ solid solutions, as well as the appearance of a second phase, hexagonal α-Mg(BH₄)₂, at higher magnesium contents. All vibrational frequencies are shifted to higher values with increasing magnesium content. The decomposition temperature of the trigonal Mg_xMn_(1−x)(BH₄)₂ (x = 0–0.8) does not vary significantly as a function of the magnesium content (433–453 K). The desorbed gas contains mostly hydrogen and 3–7.5 mol.% diborane B₂H₆, as determined from analyses of the Mn(BH₄)₂ and Mg_0.5Mn_0.5(BH₄)₂ samples. An eutectic relation between α-Mg(BH₄)₂ and LiBH₄ is observed. The solid solution Mg_xMn_(1−x)(BH₄)₂ is a promising material for hydrogen storage as it decomposes at a similar temperature to Mn(BH₄)₂, i.e. at a much lower temperature than pure Mg(BH₄)₂ without significantly losing hydrogen weight capacity thanks to substitution of Mn by Mg up to 80 mol.%. The questions of diborane release and reversibility remain to be addressed.

The synthesis of a novel alkali-metal aluminium borohydride NaAl(BH₄)_xCl_4−x from NaBH₄ and AlCl₃ using a solid state metathesis reaction is described. Structure determination was carried out using synchrotron powder diffraction data and vibrational spectroscopy. An orthorhombic structure (space group Pmn2₁) is formed which contains Na⁺ cations and complex [Al(BH₄,Cl)₄]⁻anions. Due to the high chlorine content (1 ≤ x ≤ 1.43) the hydrogen density of the borohydride is only between 2.3 and 3.5 wt.% H₂ in contrast to the expected 14.6 wt.% for chlorine free NaAl(BH₄)₄. The decomposition of NaAl(BH₄)_xCl_4−x is observed in the target range for desorption at about 90 °C by differential scanning calorimetry (DSC), in situ Raman spectroscopy and synchrotron powder X-ray diffraction. Thermogravimetric analysis (TG) shows extensive mass loss indicating the loss of H₂ and B₂H₆ at about 90 °C followed by extensive weight loss in the form of chloride evaporation.

YMn₂ forms either interstitial YMn₂H_x hydrides for x ≤ 4.5 or a complex YMn₂H₆ hydride when submitted to high hydrogen pressure. These compounds have been studied by inelastic neutron scattering (INS) in order to clarify the different modes of H vibration. The INS spectra of YMn₂H_x hydrides are strongly dependent on the H content. YMn₂H₆ and YMn₂D₆ show broad bands, also observed by Raman and IR spectroscopy, assigned to H–Mn–H (or D) and Mn–H bending and stretching modes. Both ErMn₂D₆ and ErMn_1.8Fe_0.2D₆ show, in addition to the H vibration mode, an intense band at 215 cm⁻¹ which has been attributed to a magnetic excitation of Er³⁺ in view of its momentum transfer dependence.

Size Exclusion Chromatography (SEC) on a semi-preparative scale (10 mg and more) was used to size-select ultrasmall gold nanoclusters (< 2 nm) from polydisperse mixtures. In particular, the ubiquitous byproducts of the etching process towards Au₃₈(SR)₂₄ (SR: thiolate) clusters were separated and gained in high monodispersity (based on mass spectrometry). The isolated fractions were characterized by UV/Vis spectroscopy, MALDI mass spectrometry and electron microscopy. Most notably, the separation of Au₃₈(SR)₂₄ and Au₄₀(SR)₂₄ clusters is demonstrated.

Nanofluids have been proposed to improve the performance of microchannel heat sinks. In this paper, we present a systematic characterization of aqueous silica nanoparticle suspensions with concentrations up to 31  vol %. We determined the particle morphology by transmission electron microscope imaging and its dispersion status by dynamic light scattering measurements. The thermophysical properties of the fluids, namely, their specific heat, density, thermal conductivity, and dynamic viscosity were experimentally measured. We fabricated microchannel heat sinks with three different channel widths and characterized their thermal performance as a function of volumetric flow rate for silica nanofluids at concentrations by volume of 0%, 5%, 16%, and 31%. The Nusselt number was extracted from the experimental results and compared with the theoretical predictions considering the change of fluids bulk properties. We demonstrated a deviation of less than 10% between the experiments and the predictions. Hence, standard correlations can be used to estimate the convective heat transfer of nanofluids. In addition, we applied a one-dimensional model of the heat sink, validated by the experiments. We predicted the potential of nanofluids to increase the performance of microchannel heat sinks. To this end, we varied the individual thermophysical properties of the coolant and studied their impact on the heat sink performance. We demonstrated that the relative thermal conductivity enhancement must be larger than the relative viscosity increase in order to gain a sizeable performance benefit. Furthermore, we showed that it would be preferable to increase the volumetric heat capacity of the fluid instead of increasing its thermal conductivity.

For nine solvents of various polarity (from cyclohexane to water), the solvatochromic shifts of the lowest absorption band of coumarin 153 are evaluated using a computational method based on frozen-density embedding theory [Wesolowski and Warshel, J. Chem Phys., 1993, 97, 9050, and subsequent articles]. In the calculations, the average electron density of the solvent 〈ρ_B(r→)〉 is used as the frozen density. 〈ρ_B(r→)〉 is evaluated using the statistical-mechanical approach introduced in Kaminski et al., J. Phys. Chem. A, 2010, 114, 6082. The small deviations between experimental and calculated solvatochromic shifts (the average deviation equals to about 0.02 eV), confirm the adequacy of the key approximations applied: (a) in the evaluation of the average effect of the solvent on the excitation energy, using the average density of the solvent instead of averaging the shifts over statistical ensemble and (b) using the approximant for the bi-functional of the non-electrostatic component of the orbital-free embedding potential, are adequate for chromophores which interact with the environment by non-covalent bonds. The qualitative analyses of the origin of the solvatochromic shifts are made using the graphical representation of the orbital-free embedding potential.

Shifts in the excitation energy of the organic chromophore, cis-7-hydroxyquinoline (cis-7HQ), corresponding to the π→π^* transition in cis-7HQ and induced by the complexation with a variety of small hydrogen-bonded molecules, obtained with the frozen-density embedding theory (FDET), are compared with the results of the supermolecular equation-of-motion coupled-cluster (EOMCC) calculations with singles, doubles, and non-iterative triples, which provide the reference theoretical data, the supermolecular time-dependent density functional theory (TDDFT) calculations, and experiment. Unlike in the supermolecular EOMCC and TDDFT cases, where each complexation-induced spectral shift is evaluated by performing two separate calculations, one for the complex and another one for the isolated chromophore, the FDET shifts are evaluated as the differences of the excitation energies determined for the same many-electron system, representing the chromophore fragment with two different effective potentials. By considering eight complexes of cis-7HQ with up to three small hydrogen-bonded molecules, it is shown that the spectral shifts resulting from the FDET calculations employing non-relaxed environment densities and their EOMCC reference counterparts are in excellent agreement with one another, whereas the analogous shifts obtained with the supermolecular TDDFT method do not agree with the EOMCC reference data. The average absolute deviation between the complexation-induced shifts, which can be as large, in absolute value, as about 2000 cm^-1, obtained using the non-relaxed FDET and supermolecular EOMCC approaches that represent two entirely different computational strategies, is only about 100 cm^-1, i.e., on the same order as the accuracy of the EOMCC calculations. This should be contrasted with the supermolecular TDDFT calculations, which produce the excitation energy shifts that differ from those resulting from the reference EOMCC calculations by about 700 cm^-1 on average. Among the discussed issues are the choice of the electronic density defining the environment with which the chromophore interacts, which is one of the key components of FDET considerations, the basis set dependence of the FDET, supermolecular TDDFT, and EOMCC results, the usefulness of the monomer vs supermolecular basis expansions in FDET considerations, and the role of approximations that are used to define the exchange-correlation potentials in FDET and supermolecular TDDFT calculations.

The femtosecond-resolved evolution of the emission spectrum of the important conjugated polymer poly(3-hexylthiophene) (P3HT) is presented. Detailed fluorescence up-conversion spectroscopy was performed on P3HT solid-state films and on P3HT in chlorobenzene solution. Two excitation wavelengths and several emission wavelengths, covering the entire fluorescence spectrum, were used. The data were complemented by polarization-sensitive measurements. Our global analysis allowed a reconstruction of the time-resolved emission spectra with 200 fs temporal resolution, so that spectral changes due to the early relaxation processes following π–π* interband absorption in the pristine polymer could be comprehensively characterized. Absorption occurs in isolated polymer chains in solution and in the solid state (including interchain interactions) for the film. In both cases, we find evidence of delocalization of the electrons and holes formed in the energy bands directly after photoexcitation with excess energy. This is followed by ultrafast (~100 fs) self-localization of the primary photoexcitation and by relatively slow exciton formation (~1 ps). Further relaxation occurs with time constants ranging from hundreds of femtoseconds to tens of picoseconds, due to exciton hopping to sites with lower energy and to a slow conformational planarization of the polymer backbone. Depolarization, a spectral red shift, and important changes in the vibronic structure are observed as a consequence of this relaxation. Finally, relaxed intrachain and interchain singlet excitons are formed in solution and film, respectively, on a 100–200 ps time scale. They decay with a ~500 ps time constant, by intersystem crossing in solution and by nonradiative recombination in the film. Our results are consistent with and strongly support the conclusions we obtained from a similar time-resolved fluorescence study of the polymer PCDTBT (J. Am. Chem. Soc.2010, 132, 17459): ultrafast charge separation in polymer:fullerene blends seems to occur before localization of the primary excitation to form a bound exciton.

The fluorescence lifetime of the radical cation of N,N,N′,N′-tetramethyl-p-phenylenediamine (Wurster's blue) decreases from 260 ps at 82 K to 200 fs at room temperature. Calculations indicate a small barrier between the excited-state minimum (D₁ min) and a conical intersection (CI) of the excited and ground state potentials. The intersection is reached within 200 fs upon torsion of one of the C—N bonds.

A novel N-substituted 4-methoxy-1,8-naphthalimide (NAFTA 8) especially designed for fluorescent labeling of gold nanoparticles has been synthesized. NAFTA 8 bears a long methylene chain at the imide N atom and has a terminal SH group, which enables its chemical binding to gold nanostructures. The longest wavelength absorption maximum of NAFTA 8 in chloroform is at 370 nm, the fluorescent maximum is at 430 nm and the fluorescent quantum yield is 0.95. The newly synthesized fluorophore is applied for functionalization of gold nanoparticles with diameter 1.5 ± 0.5 nm prepared through chemical reduction. The obtained Monolayer Protected Clusters are characterized by elemental analysis, TEM, XPS, FT-IR, absorption and fluorescence spectroscopy. The performed investigations provide evidence for the formation of chemical bond between the thiol ligand and the gold surface. They also show that the obtained metal/dielectric 3D structures are highly fluorescent.

Using bottom-up and self-assembly processes, large scale layered arrays of strongly coupled gold nanoparticles with controllable dimensions were fabricated. By carefully adjusting the distance between adjacent gold nanoparticle arrays, it is possible to control the coupling of the localized surface plasmon polariton resonance as sustained by individual gold nanoparticles. A greater interaction is observed at smaller separations, leading to a well pronounced shift in the spectral position of resonances that can be adjusted with high precision. Simulations showed good agreement with experimental observations in an in-depth investigation of such structures, suggesting minimal separations of only one nanometer are achieved.

The excited-state dynamics of eosin B (EB) at dodecane/water and decanol/water interfaces has been investigated with polarization-dependent and time-resolved surface second harmonic generation. The results of the polarization-dependent measurements vary substantially with (1) the EB concentration, (2) the age of the sample, and (3) the nature of the organic phase. All of these effects are ascribed to the formation of EB aggregates at the interface. Aggregation also manifests itself in the time-resolved measurements as a substantial shortening of the excited-state lifetime of EB. However, independently of the dye concentration used, the excited-state lifetime of EB at both dodecane/water and decanol/water interfaces is much longer than in bulk water, where the excited-state population undergoes hydrogen-bond-assisted non-radiative deactivation in a few picoseconds. These results indicate that hydrogen bonding between EB and water molecules at liquid/water interfaces is either much less efficient than in bulk water or does not enhance non-radiative deactivation. This strong increase of the excited-state lifetime of EB at liquid/water interfaces opens promising avenues of applying this molecule as a fluorescent interfacial probe.

The connection of two Cr^III sensitizers around a central Er^III acceptor in a self-assembled cation provides high local metal concentrations that favor efficient nonlinear energy transfer upconversion luminescence (see picture). Upon selective low-energy near-infrared irradiation of Cr^III-centered transitions, 1 displays an unprecedented molecular two-photon upconverted green Er^III-centered emission.

We investigated by optical microscopy the thermal spin transition in single crystals of [Fe(bbtr)₃](ClO₄)₂ (bbtr = 1,4-di(1,2,3-triazol-1-yl) butane). The growth of the low-spin phase was observed for different crystal orientations and sizes. The process always started from a corner of the crystal but its further development depended on the size, shape and thermal history of the crystal. In crystals of smaller size, under isothermal conditions, the low-spin phase developed in a continuous way, through the propagation of a rather well defined transformation front, with a higher propagation velocity inside the planes perpendicular to the c axis. In larger crystals the spontaneous occurrence of inhomogeneous stresses led to a stepwise propagation process.

The photocatalytic degradation of l-asparagine and l-glutamic acid over Au/TiO₂ and TiO₂ catalysts was investigated in situ by attenuated total reflection infrared (ATR-IR) in combination with modulation excitation spectroscopy. Oxalate was detected on the catalyst surface, which has not been reported before for degradation of amino acids by studies focusing on intermediates in solution. The ATR-IR spectra provide valuable information on the fate of the nitrogen. Ammonium was detected, in agreement with previous studies. Most importantly, strong signals of cyanide were observed, and this assignment has been corroborated by ¹⁵N labeling experiments. Cyanide was not reported before, to the best of our knowledge, for the photocatalytic degradation of amino acids. Cyanide was formed in the presence and the absence of gold particles on the TiO₂ surface. The cyanide leads to leaching of gold via Au(CN)₂⁻ species that were detected in solution by mass spectrometry.

In this article we present an overview of our recent research in the fields of in situ spectroscopy, nanomaterials and chirality. Our research focuses around the spectroscopic investigation of chemical reactions taking place at solid-liquid interfaces. This research goesh and in hand with the development of experimental techniques that enable us to study interface phenomena in situ. Using such techniques we try to shed light on photocatalytic reactions like the decomposition of organic pollutants in water or the reduction of carbon dioxide. We are moreover interested in chiral surfaces and their ability to discriminate betweenen antiomers. Again this relies on special techniques that highlight the enantiodiscriminating surface-adsorbate interactions. We further more seek to transfer chirality from adsorbates to metal nanoparticles. The latter are probed by chiroptical techniques, particularly also vibrational circular dichroism (VCD). Finally, we aim at preparing metamaterials with tailored optical properties by organizing plasmonic particles in two and three dimensions.

The photophysics of two dyes from the xanthene family, eosin B (EB), and eosin Y (EY) has been investigated in various solvents by femtosecond transient absorption spectrosco- py, first, to clarify the huge disparity of the EB fluorescence lifetimes reported in literature, and, second, to understand the mechanism responsible for the ultrafast excited-state deactivation of EB in water. The excited-state lifetime of EB was found to be much shorter in water and in other protic solvents, due to the occurrence of hydrogen-bond assisted nonradiative deactivation. This mechanism is associated with the hydrogen bonds between the solvent molecules and the nitro groups of EB, which become stronger upon optical excitation due to the charge-transfer character of the excited-state. This process is not operative with EY, where the nitro groups are replaced by bromine atoms. Therefore, the excited-state lifetime of EB in solution is directly related to the strength of the solvent as a hydrogen-bond donor, offering the possibility to build a corresponding scale based on the fluorescence quantum yield or lifetime of EB. This scale of hydrogen-bonding strength could be especially useful for studies of liquid interfaces by time-resolved surface second harmonic generation.

The synthesis and the photophysical properties of the complex [Ru(TTF-dppz)₂(Aqphen)]²⁺(TTF = tetrathiafulvalene, dppz = dipyrido-[3,2-a:2′,3′-c]phenazine, Aqphen = anthraquinone fused to phenanthroline via a pyrazine bridge) are described. In this molecular triad excitation into the metal−ligand charge transfer bands results in the creation of a long-lived charge separated state with TTF acting as electron donor and anthraquinone as terminal acceptor. The lifetime of the charge-separated state is 400 ns in dichloromethane at room temperature. A mechanism for the charge separation involving an intermediate charge-separated state is proposed based on transient absorption spectroscopy.

Analysis of time-resolved anisotropy of transient absorption enabled determination of room temperature ground and excited state rate constants for intramolecular double hydrogen transfer in two similar porphycenes, one of them with symmetric and the other, with asymmetric character of a double minimum potential for hydrogen motion. The perturbation preserves a quasi-symmetric minimum in S₀, but the rate decreases approximately two times. In S₁, the perturbed potential becomes strongly asymmetric, and the downhill hydrogen transfer occurs with a rate higher than that observed for a symmetrical compound.

The excited-state dynamics of aminostilbazolium dyes is known to be dominated by nonradiative deactivation through large-amplitude motion. In order to identify the coordinate(s) responsible for this process, the excited-state lifetimes of two dialkylaminostyryl-methylpyridinium iodides have been measured at liquid−liquid interfaces using time-resolved surface second harmonic generation. We found that the decay time of the excited-states of both compounds was increasing with the viscosity of the apolar phase, consisting of n-alkanes of varying length, but was unaffected by that of the polar phase, made of water/glycerol mixtures. This indicates that the nonradiative deactivation is associated with the twist of the dialkylaniline group, which is located in the apolar part of the molecule.

Whereas the neat polymeric iron(II) compound [Fe(bbtr)₃](ClO₄)₂, bbtr = 1,4-di(1,2,3-triazol-1-yl)butane, shows a quantitative spin transition triggered by a crystallographic phase transition centered at 107 K with a 13 K wide hysteresis, the iron(II) complexes in the diluted mixed crystals [Fe_xZn_1−x(bbtr)₃](ClO₄)₂, x = 0.02 and 0.1, stay predominantly in the ⁵T₂ high-spin state down to cryogenic temperatures. However, the ¹A₁ low-spin state can be populated as metastable state via irradiation into the spin-allowed ⁵T₂→⁵E ligand-field transition of the high-spin species in the near-infrared. The quantum efficiency of the light-induced conversion is approximately 10% at low temperatures and decreases rapidly above 160 K. The lifetime of the light-induced low-spin state decreases from 15 days at 40 K to 30 ns at 220 K, that is, by 14 orders of magnitude. In the high-temperature regime the activation energy for the low-spin→high-spin relaxation is 1840(20) cm⁻¹.

The structural and vibrational properties of the isostructural compounds Ca₂FeH₆ and Sr₂RuH₆ are determined by periodic DFT calculations and compared with their previously published experimental crystal structures as well as new experimental vibrational data. The analysis of the vibrational data is extended to the whole series of alkaline-earth iron and ruthenium hydrides A₂TH₆ (A = Mg,Ca,Sr; T = Fe, Ru) in order to identify correlations between selected frequencies and the T-H bond length. The bulk moduli of Ca₂FeH₆ and Sr₂RuH₆ have also been determined within DFT. Their calculated values prove to compare well with the experimental values reported for Mg₂FeH₆ and several other compounds of this structure.

The high energy of hydrogen vibrations in solids is the origin of their strong impact on thermodynamic properties. The peculiar structure of complex hydrides amplifies this impact. We shed light on the vibrational properties of three allotropes of Ca(BH₄)₂ using density-functional theory calculations, infrared spectroscopy, and inelastic neutron scattering. We show that the vibrational properties of Ca(BH₄)₂ depend on the specific phase and are hitherto the origin of their differences in stability.

We propose a new approach to determine a suitable zeroth-order wavefunction for multiconfigurational perturbation theory. The same ansatz as in complete active space (CAS) wavefunction optimization is used but it is split in two parts, a principal space (A) and a much larger extended space (B). Löwdin's partitioning technique is employed to map the initial eigenvalue problem to a dimensionality equal to that of (A) only. Combined with a simplified expression for the (B) portion of the wavefunction, we are able to drastically reduce the storage and computational demands of the wavefunction optimization. This scheme is used to produce reference wavefunctions and energies for subsequent second-order perturbation theory (PT2) corrections. Releasing the constraint of computing the exact CAS energy and wavefunction prior to the PT2 treatment introduces a nonstandard paradigm for multiconfigurational methods. Based on the results of test calculations, we argue that principal parts with only few percents of the total number of CAS configurations could provide final multiconfigurational PT2 energies of the same accuracy as in the standard paradigm. In the future, algorithmic improvements for this scheme will bring into reach active spaces much beyond the present limit of CAS-based methods, therefore allowing for accurate studies of systems featuring strong correlation.

Several new studies of Mg(BH₄)₂ are reported. A 1:1 LiBH₄:Mg(BH₄)₂ mixture was studied by in situ synchrotron X-ray diffraction and reveals an eutectic behavior with the eutectic composition more rich in Mg(BH₄)₂, and the eutectic temperature lower than 456 K. No dual cation compound was observed in this experiment.

New vibrational spectra including INS data have been obtained and are compared with theoretical DFT calculations and recent NMR studies, showing good agreement.

Single crystals of Hydroxyethylammonium L – tartrate monohydrate [HEALT] have been grown by slow evaporation technique using water as a solvent. The structural and vibrational properties of the crystals were studied. Besides these characterizations ab initio quantum chemical calculations have been performed at HF/6-31G (d) level to derive first order hyperpolarizability. It is shown that the first order hyperpolarizability is found to be 14.2 times more than that of urea. The characteristic vibrational frequencies obtained from polarized Raman spectra in different scattering configurations have been assigned based on the complete factor group analysis. Vibrational analysis of IR and Raman reveals that the charge transfer interaction must be responsible for nonlinear optical (NLO) properties of the present system. The UV absorption measurements have also been carried out to confirm the utility of the material for optical applications.

The importance of the nonelectrostatic component of the embedding potential is investigated by comparing the complexation induced shifts of the iso-g obtained in embedding calculations to its supermolecular counterparts. The analyses are made in view of such multilevel simulations, for which supermolecular strategy is either impractical or impossible, such as the planned simulations for the whole enzyme ferredoxin oxidoreductase. For the biliverdin radical surrounded by a few amino acids, it is shown that the embedding potential comprising only Coulomb terms fails to reproduce even qualitatively the shifts evaluated from supermolecular calculations. The nonelectrostatic component of the exact embedding potential is a bifunctional of two electron densities [Wesolowski and Warshel, J. Phys. Chem. 1993, 97, 8050; Wesolowski, Phys. Rev. A 2008, 77, 012504]. Therefore we analyze in detail both the quality of the approximant for the bifunctional and the importance of the choice of the electron densities at which it is evaluated in practical calculations.

The recently developed second-order perturbation theory restricted active space (RASPT2) method has been benchmarked versus the well-established complete active space (CASPT2) approach. Vertical excitation energies for valence and Rydberg excited states of different groups of organic (polyenes, acenes, heterocycles, azabenzenes, nucleobases, and free base porphin) and inorganic (nickel atom and copper tetrachloride dianion) molecules have been computed at the RASPT2 and multistate (MS) RASPT2 levels using different reference spaces and compared with CASPT2, CCSD, and experimental data in order to set the accuracy of the approach, which extends the applicability of multiconfigurational perturbation theory to much larger and complex systems than previously. Relevant aspects in multiconfigurational excited state quantum chemistry such as the valence−Rydberg mixing problem in organic molecules or the double d-shell effect for first-row transition metals have also been addressed.

The photophysics and excited-state dynamics of two dyads consisting of either a free-base or a zinc-tetraphenylporphyrin linked through a rigid bridge to a core-substituted naphthalenediimide (NDI) have been investigated by femtosecond-resolved spectroscopy. The absorption and fluorescence spectra differ substantially from those of the individual units, pointing to a substantial coupling and to a delocalisation of the excitation over the whole molecule, as confirmed by quantum chemistry calculations. A strong dependence of their excited-state dynamics on the solvent polarity has been observed. In toluene, the fluorescence quantum yield of the dyads is of the order of a few percent and the main decay channel of the emitting state is proposed as intersystem-crossing to the triplet state. However, in a medium polarity solvent like dichloromethane, the emitting state undergoes charge separation from the porphyrin to the NDI unit within 1–3 ps, and the ensuing charge-separated state recombines in about 10–20 ps. This solvent dependence can be explained by the weak driving force for charge separation in polar solvents and the large electronic coupling between the porphyrin and NDI moieties, making charge separation a solvent-controlled adiabatic process.