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 of soluble oligomers and polymers consisting of substituted and unsubstituted thiophene-2,5-diyl repeat units. Polymers derived from these oligomers 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 cycling to a potential just positive of the onset of oxidation, affords films of the corresponding dimers that are insoluble in acetonitrile but 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 containing monomer, dimer, and polymer. Chemical oxidation of dialkylated terthiophene and quarterthiophene affords dimeric and polymeric materials that are useful for comparisons to intermediates formed during electrochemical polymerization. The oligomers and polymers were characterized by NMR, infrared, and visible spectroscopy, cyclic voltammetry, and X-ray diffraction.