THIOPHENE-ALKYLTHIOPHENE COPOLYMERS FROM SUBSTITUTED DIALKYLOLIGOTHIOPHENES

Oxidation of a series of dioctyloligothiophenes, in which the terminal thiophene rings are substituted at the S-position, affords mixtures o f soluble oligomers and polymers consisting of substituted and unsubst ituted thiophene-2,5-diyl repeat units. Polymers derived from these ol igomers have conjugation lengths approaching that of 100% head-to-tail PATs and have high electrical conductivities (similar to 40 S cm(-1)) . Electrochemical oxidation of low concentrations of oligomers, by cyc ling to a potential just positive of the onset of oxidation, affords f ilms of the corresponding dimers that are insoluble in acetonitrile bu t that can be spectroscopically characterized in chlorinated solvents. These dimers are intermediates in the formation of the corresponding polymers. Electrochemical oxidation at high monomer concentrations or at potentials far positive of the oxidation potential affords films co ntaining monomer, dimer, and polymer. Chemical oxidation of dialkylate d terthiophene and quarterthiophene affords dimeric and polymeric mate rials that are useful for comparisons to intermediates formed during e lectrochemical polymerization. The oligomers and polymers were charact erized by NMR, infrared, and visible spectroscopy, cyclic voltammetry, and X-ray diffraction.