The ligand 3-chloro-6-dipicolylamino-1,2,4,5-tetrazine (Cl-TTZ-dipica) 1, prepared by the direct reaction between 3,6-dichloro-1,2,4,5-tetrazine and di(2-picolyl)-amine, afforded a series of four neutral transition metal complexes formulated as [Cl-TTZ-dipica-MCl₂]₂, with M = Zn(II) 2a, Cd(II) 2b, Mn(II) 2c and Co(II) 2d, when reacted with the corresponding metal chlorides. The dinuclear structure of the isostructural complexes was disclosed by single crystal X-ray analysis, clearly indicating the formation of [M^II-(m-Cl)₂M^II] motifs and the involvement of the amino nitrogen atom in semi-coordination with the metal centers, thus leading to distorted octahedral coordination geometries. Moreover, the chlorine atoms, either coordinated to the metal or as substituent on the tetrazine ring, engage respectively in specific anion-p intramolecular and intermolecular interactions with the electron poor tetrazine units in the solid state, thus controlling the supramolecular architecture. Modulation of the emission properties is observed in the case of the Zn(II) and Cd(II) complexes when compared to the free ligand. A striking difference is observed in the magnetic properties of the Mn(II) and Co(II) complexes. An antiferromagnetic coupling takes place in the dimanganese(II) compound (J = -1.25 cm^-1) while the Co(II) centers are ferromagnetically coupled in the corresponding complex (J = +0.55 cm^-1), the spin Hamiltonian being defined as H = -JS_A^.S_B.

Bis(thiomethyl)- and bis(thiohexyl)-tetrathiafulvalene-bromo-benzothiadiazoles, containing electron donor tetrathiafulvalene (TTF) and electron acceptor benzothiadiazole (BTD) units, have been prepared by Stille coupling reactions between the TTF-SnMe₃ precursors and BTD-Br₂. In another series of experiments, TTF-acetylene-BTD compounds have been synthesized by Sonogashira coupling between either TTF-acetylenes and BTD-Br₂ in low yields, or TTF-iodine and BTD-acetylene in moderate yields. In the compound TTF-C≡C-BTD the TTF and BTD units are coplanar in the solid state, as shown by the single crystal X-ray structure, and there is segregation in the packing between the donor and acceptor units. All the derivatives have good electron donor properties, as determined by cyclic voltammetry measurements, and they can also be reversibly reduced thanks to the presence of the BTD moiety. UV-visible spectroscopy and photophysical investigations show the presence of an intramolecular charge transfer (ICT) band and an emission band originating from the charge transfer. Both the absorption and the emission are modulated by the substitution scheme and the insertion of the acetylenic bridge.

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 structurally characterized tetrathiafulvalene-1,2,4,5-tetrazine donor–acceptor system shows redox tuneable intramolecular charge transfer, solvatochromic and electrochromic behaviour. Attachment of a dipicolyl-amine chelating unit affords a multifunctional ligand, which allows the preparation of the ZnCl₂ complex in which an anion-Ï€ interaction is seen.

Electrochemical and photophysical analysis of new donor–acceptor systems 2 and 3, in which a benzothiadiazole (BTD) unit is covalently linked to a tetrathiafulvalene (TTF) core, have verified that the lowest excited state can be ascribed to an intramolecular-charge-transfer (ICT) Ï€(TTF)→π*(benzothiadiazole) transition. Owing to better overlap of the HOMO and LUMO in the fused scaffold of compound 3, the intensity of the ¹ICT band is substantially higher compared to that in compound 2. The corresponding CT fluorescence is also observed in both cases. The radical cation TTF^+. is easily observed through chemical and electrochemical oxidation by performing steady-state absorption experiments. Interestingly, compound 2 is photo-oxidized under aerobic conditions.