Electrochemical and spectroelectrochemical investigations of small-bandgap π-conjugated polymers and their precursors

The film-formation behaviour of 1,3-dihydro-bis-[1,3-(2-thienylmethylidene)]-isothianaphthene (2) (as a model compound for oligomerization of arenemethylidenes) under anodic oxidation has been investigated by cyclic voltammetry under a variety of reaction conditions. Detailed cyclovoltammetric and spectroelectrochemical studies of the oxidation processes of 5,5′-bis-(di-phenylmethylidene)- 2,2′,5,5′-tetrahydro-2,2′-bithiophene (3), 5,5′-bis-(phenyl-p-tolylmethylidene)-2,2′,5,5′-tetrahydro-2,2′-bithiophene (4), 5.5′-bis-(phenyl- 2-thienyl-methylidene)-2,2′,5,5′-tetrahydro-2,2′-bi-thiophene (5) and 5,5′-bis-(di-2-thienylmethylidene)-2,2′,5,5′-tetrahydro-2,2′- bithiophene (6) reveal two reversible oxidation steps and no oligomerization as observed for 2. Electrochemical and spectroelectrochemical investigations of electropolymerized cyanosubstituted p-conjugated polymers 7b and 8b with a small bandgap derived from β,β′-di-(2- thienyl)-β,β′-(2,5-thiophene)-diacrylnitrile (7a) and substituted dithienylethylene 8a are reported. The electronic influence of two cyano groups and steric hindrance avoid the film formation of 1,2-dicyano-1,2-di-2-(thienyl)ethylene (9a).