A large pi-conjugated chromophore composed of two dipyrido[3,2-a:2’,3’-c]phenazine (dppz) units directly fused to the central tetrathiafulvalene (TTF) core, has been prepared as a bridging ligand, and its strong binding ability to Ru²⁺ forming a new dinuclear complex is presented. The electronic absorption and luminescence and the electrochemical behaviour of the free ligand as well as the Ru²⁺ complex have been investigated in detail. The free ligand shows a very strong band in the UV region consistent with ligand centred Ï€-Ï€* transitions and an intense broad band in the visible region corresponding to an intramolecular charge transfer (ILCT) transition. Upon coordination, a metal-to-ligand charge transfer (MLCT) appears at 22520 cm^-1 while the ILCT band is bathochromically shifted by 1620 cm^-1. These electrochemically amphoteric chromophores have also been characterized by spectroelectrochemical methods. The oxidized radical species of the free ligand show a strong tendency to undergo aggregation, in which long-distance attractive interactions overcome the electrostatic repulsion. Moreover, these two new chromophores reveal an ILCT fluorescence with large solvent-dependent Stokes shifts and quantum efficiencies of 0.052 for the free ligand and 0.016 for its dinuclear Ru²⁺ complex in CH₂Cl₂.

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 Ï€-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.

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.

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.