Effects of structural factors on the π-dimerization and/or disproportionation of the cation radical of extended TTF containing thiophene-based π-conjugated spacers
Résumé
The electrochemical and chemical oxidation of extended TTF 4 and 5 are analysed by cyclic voltammetry, Visible/NIR and ESR spectroscopies, and the X-ray structures of the new salts 5BF4(CH2Cl2) and 4ClO4(THF)1/2 are presented. The effects of structural factors on the -dimerization or the disproportionation reaction of the cation radical are shown. The oxidation of compound 4 presents the successive formation of stable cation radical and dication species both in dichloromethane (DCM) and in a CH3CN/THF mixture. In contrast, for compound 5, the stability of the oxidation states strongly depends on the nature of the solvent. In DCM, the oxidation of 5 proceeds by two close one-electron transfers while in CH3CN/THF the dication is directly formed via a two-electron process. The X-ray structures of the two salts reveal the formation of -dimers of cation radical. While the dimer (52)2+ is due mainly to - interactions between the conjugating spacer, the multiplication of the sulfur atoms in compound 4 contributes to stabilize the dimer by the combined effects of S-S and - interactions. Visible/NIR and ESR experiments confirm the higher tendency of 4+. to dimerize with the occurrence of dimer and monomer in solution, while for 5+. only the monomer is detected in DCM. On the other hand, by dissolution of 5BF4(CH2Cl2) in CH3CN, only the neutral and the dicationic states of compounds 5 are observed owing to the disproportionation reaction.