THIOPHENE OLIGOMERS AS POLYTHIOPHENE MODELS .2. ELECTROCHEMISTRY AND INSITU ESR OF END-CAPPED OLIGOTHIENYLS IN THE SOLID-STATE - EVIDENCE FOR PI-DIMERIZATION OF HEXAMERIC POLARONS IN POLYTHIOPHENE

Thin films of thiophene oligomers (n = 4, 6, 8, and 10) methyl-protected toward anodic coupling at the terminal alpha positions were investigated by cyclic voltammetry and in situ ESR in acetonitrile. Reversible oxidation goes from a single one-electron step (tetramer) to a single two-electron step (octamer and decamer) through two separate one-electron steps (hexamer). ESR indicates strong magnetic dimerization for the one-electron-oxidized hexamer. The close resemblance of the electrochemical and ESR behavior of the hexamer with that of polythiophene suggests that oxidation of the latter occurs via hexameric spin-dimerized polarons. The hexameric model is discussed taking account of the oligomeric nature of polythiophene.