ELECTROCHEMICAL AND ELECTRONIC-PROPERTIES OF NEUTRAL AND OXIDIZED SOLUBLE ORTHOGONALLY-FUSED THIOPHENE OLIGOMERS

The chemical and electrooxidation of spiro-fused thiophene trimers, SIII, and spiro-fused thiophene heptamers, SVII, with terminal alpha-Si(CH3)3 and beta-CH3 groups were studied in CH2Cl2 at room temperature. The heptamer segments in SVII oxidize stepwise to produce the mono radical cation, the bis(radical cation), the radical cation/dication, and the bis(dication), respectively. The existence of these intermediate ions was confirmed by vis/near-IR and ESR analyses. The presence of anodic peaks at different potentials for the removal of the first and second electron from SIII and SVII suggests that some interaction exists between the radical cation and the neutral oligomers. However, once both oligomers are oxidized, there appears to be no significant electronic interactions between the orthogonally positioned heptamer cations except possibly some weak magnetic coupling. With SIII, the trimer segments oxidize at fairly anodic potentials, and the four sequential intermediates are not observed because the less stable cations probably dimerize to form a bis(spiro structure) containing a thiophene hexamer cation.