Mechanism of the oxidative dimerization of DTF (dithiafulvenes) to form TTF vinylogues (tetrathiafulvalenes) has been investigated by cyclic voltammetry at low and high scan rates for a series of substituted DTF. It involves first the formation of the cation radical which couples to form the protonated dication. This dication slowly deprotonates to give the final TTF (k ) 0.5-1 s -1 ). The dimerization rate constant was found to be in the range of k dim ) (2-4) × 10 8 L mol -1 s -1 and not vary much with the nature of the substituent.

Oxidation of a series of TTF vinylogues has been investigated in acetonitrile and dichloromethane. Depending on the substituent and the solvent, two single-electron transfers or one two-electron process was observed. Density functional modeling calculations and detailed analysis of the electrochemical behavior show that the unusual redox behavior for short-length TTF vinylogues is due to substantial conformation changes concerted with the electron transfers. Flash photolysis and spectroelectrochemistry experiments were also performed to confirm this conclusion. Through fine-tuning of the molecule structure and substituent choice, it is possible to control the relative stabilities of the different redox species. At one end, this leads to situations where the second electron transfer is much easier than the first one. At the other end, opposite situations are observed with a large increase of the separation between the first and second oxidation potentials by comparison to similar TTF without steric hindrance. The inner sphere reorganization energies remain modest (0.35−0.45 eV), allowing a fast passage between the different conformations during the electron transfers.