Syntheses of New Alternating CT-Type Copolymers of Thiophene and Pyrido[3,4-b]pyrazine Units: Their Optical and Electrochemical Properties in Comparison with Similar CT Copolymers of Thiophene with Pyridine and Quinoxaline

Abstract

Four kinds of new π-conjugated copolymers of electron-donating thiophene with highly electron-withdrawing pyrido[3,4-b]pyrazine derivatives have been prepared by using the Stille reaction and electrochemical oxidative polymerization in high yields, and their optical and electrochemical properties have been compared with those of previously reported CT-type π-conjugated polymers. Chemically prepared polymers show an [η] value of about 0.3 dL g-1. The π−π* absorption bands (λmax = ca. 633 nm) of the copolymers are observed at a longer wavelength by about 30 nm than those of similar CT-type copolymers of thiophene with pyridine and quinoxaline. These UV−vis data are considered to reflect a stronger CT interaction between thiophene and pyrido[3,4-b]pyrazine, which has a higher electron-withdrawing ability than pyridine and quinoxaline. The copolymers are electrochemically active in both oxidation and reduction regions. In the reduction (n-doping) region, the copolymers show normal three couples of n-doping an...