Ru(II) complexes with chelating ligands, 4′,5′-ethylenedithiotetrathiafulvenyl[4,5-f][1,10]phenanthroline (L1), 1,3-dithiole-2-thiono[4,5-f][1,10]phenanthroline (L2), and 1,3-dithiole-2-ono[4,5-f][1,10]phenanthroline (L3), have been prepared and their structural, electrochemical, and photophysical properties investigated. Density functional theory (DFT) calculations indicate that the highest occupied molecular orbital of [Ru(bpy)₂(L1)](PF₆)₂ (1) is located on the tetrathiafulvalene (TTF) subunit and appears ≈0.6 eV above the three Ru-centered d orbitals. In agreement with this finding, 1 exhibits three reversible oxidations: the two at lower potentials take place on the TTF subunit, and the one at higher potential is due to the Ru³⁺/Ru²⁺ redox couple. Complexes [Ru(bpy)₂(L2)](PF₆)₂ (2) and [Ru(bpy)₂(L3)](PF₆)₂ (3) exhibit only the Ru³⁺/Ru²⁺-related oxidation. The optical absorption spectra of all complexes reveal a characteristic metal-to-ligand charge transfer (MLCT) band centered around 450 nm. In addition, in the spectrum of 1 the MLCT band is augmented by a low-energy tail that extends beyond 500 nm and is attributed to the intraligand charge transfer (ILCT) transition of L1, according to time-dependent DFT calculations. The substantial decrease in the luminescence quantum yield of 1 compared to those of 2 and 3 is attributed to the reductive quenching of the emissive state via electron transfer from the TTF subunit to the Ru³⁺ center, thus allowing nonradiative relaxation to the ground state through the lower-lying ILCT state. In the presence of O₂, complex 1 undergoes a photoinduced oxidative cleavage of the central Câ•�C bond of the TTF fragment, resulting in complete transformation to 3. This photodegradation process was studied with ¹³C NMR and optical absorption spectroscopy.

Palladium-catalyzed cross-coupling reactions between chlorinated 1,3,5-triazines (TZ) and tetrathiafulvalene (TTF) trimethyltin derivatives afford mono- and C₃ symmetric tris(TTF)-triazines as donor–acceptor compounds in which the intramolecular charge transfer (ICT) is modulated by the substitution scheme on TTF and TZ and by chemical or electrochemical oxidation. The TTF-TZ-Cl₂ and (SMe)₂TTF-TZ-Cl₂ derivatives show fully planar structures in the solid state as a consequence of the conjugation between the two units. Electrochemical and photophysical investigations, supported by theoretical calculations, clearly demonstrate that the lowest excited state can be ascribed to the intramolecular charge transfer (ICT) Ï€(TTF)→π*(TZ) transition. The tris(TTF) compound [(SMe)₂TTF]₃-TZ shows fluorescence when excited in the ICT band, and the emission is quenched upon oxidation. The radical cations TTF^+• are easily observed in all of the cases through chemical and electrochemical oxidation by steady-state absorption experiments. In the case of [(SMe)₂TTF]₃-TZ, a low energy band at 5000 cm^–1, corresponding to a coupling between TTF^+• and TTF units, is observed. A crystalline radical cation salt with the TTF-TZ-Cl₂ donor and PF₆^– anion, prepared by electrocrystallization, is described.

The synthesis and photophysical properties of the complex [Fe(phen)₂(TTF-dppz)]²⁺ (TTF-dppz = 4′,5′-bis-(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2′,3′-c]phenazine, phen = 1,10-phenanthroline) are described. In this complex, excitation into the metal–ligand charge transfer bands results in the population of a high-spin state of iron(II), with a decay lifetime of approximately 1.5 ns, in dichloromethane, at room temperature. An intraligand charge transfer state can also be obtained and has a lifetime of 38 ps. A mechanism for the different states reached is proposed based on transient absorption spectroscopy.

This contribution investigates Ln^III complexes formed with a small ditopic ligand, L1, and their structural, thermodynamic and photophysical properties. The spectrophotometric and NMR titrations evidence the triangular assemblies [Ln₃(L1-H)₃]⁶⁺ at stoichiometric conditions and their properties are discussed in relation to L2-containing analogues. In addition, the dinuclear species, [Ln₂(L1-H)]⁵⁺, is observed with an excess of metal.

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.

Two tridentate and one bidentate binding strands have been anchored on a carbon atom to provide a new unsymmetrical tripodal ligand L for Ln(III) coordination. The ligand itself adopts a single conformation in solution stabilized by intramolecular hydrogen bonds evidenced in the solid state. The reaction of L with trivalent lanthanides provides different coordination complexes depending on the metal/ligand ratio. The speciation studies with selected lanthanides were performed in solution by means of NMR, ESMS, and spectrophotometric titrations. Differences in coordination properties along the lanthanide series were evidenced and may be associated with the changes in the ionic size. However, thermodynamic stability constants for the species of the same stoichiometry do not significantly vary. In addition, the structure of the dinuclear complex [Eu₂L₂]⁶⁺ has been elucidated in the solid state, where the complex crystallizes predominantly as an M-isomer. The crystal structure shows the coordination of two different ligands to each europium cation through tridentate strands, and the europium nine-coordinate sphere is completed with three solvent molecules. Finally, the results of photophysical investigations of [Eu₂L₂]⁶⁺ are in close agreement with the structural parameters determined by crystallography.

The synthesis and structural characterization of a tetrathiafulvalene-fused perylenediimide molecular dyad is presented. Its largely extendedπ-conjugation provides intense optical absorption bands over a wide spectral range. The planar functional molecule exhibits a short-livednonluminescent excited state attributed to intramolecular charge separation.

In order to study the electronic interactions in donor-acceptor ensembles as a function of pH, an efficient synthetic route to three imidazole-annulated tetrathiafulvalene (TTF) derivatives 1-3 is reported. Their electronic absorption spectra, in view of photoinduced intramolecular charge transfer, and their electrochemical behavior were investigated, and pKa values for the two protonation processes on the acceptor unit were determined in organic solvents by photometric titration. The influence of the TTF moiety on these values is discussed.

Triangular luminescent box: Self-assembly of a new multidentate receptor with europium cations results in the formation of trinuclear discrete complexes. X-ray crystallography shows that nine-coordinate cations are linked by ligands to provide a triangular complex in the solid state and in solution. Despite the coordinated solvent molecules, this topologically unusual complex exhibits remarkable luminescent properties.

A Ï€-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 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 Ï€-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 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.