Electrosynthesis and redox behavior of vinylogous TTF displaying strong conformational changes associated with electron transfers

The redox properties of a series of substituted vinylogous tertrathiafulval enes (TTF) prepared by oxidative coupling of 1,4-dithiafulvenes (DTF) have been investigated in acetonitrile and dichloromethane. The different steps of the electrodimerization mechanism have been characterized: fast electron transfer, coupling between two cation-radicals and slow deprotonation. Thr ough the substituent choice of DTF, it is possible to control the relative stabilities of the different redox species of the electrogenerated vinylogo us TTF. According to the nature and position of the substituent, the struct ural changes induced by the steric interactions lead to a compression of po tential (where the second electron is easier to remove than the first one), or on the contrary to a large increase of the separation between the first and second oxidation potentials (by comparison with similar molecules with out steric hindrance). Density functional modeling calculations and detaile d analysis of the electrochemical behavior have been used to rationalize th e substituent effect. A good agreement with the occurrence of an EE mechani sm in which the electron transfer is concerted with the conformation change s is found. The inner reorganization energies are low (0.35-0.45 eV) allowi ng a fast passage between the different conformations during the electron t ransfers. (C) 2001 Elsevier Science Ltd. All rights reserved.