LY(BENZO[1,2-B4,5-B']DITHIOPHENE-4,8-DIYLVINYLENE) - SYNTHESIS, PROPERTIES, AND ELECTRONIC-STRUCTURE OF A NEW DITHIOPHENE-FUSED P-PHENYLENEVINYLENE CONDUCTING POLYMER

A new conducting polymer poly(benzo[1,2-b:4,5ib']dithiophene-4,8-d (1) , has been synthesized by the pyrolysis of the soluble precursor polym er 2, which was itself prepared by a multistep synthesis. The polymer is burgundy, and a film has lambda(max) = 503 nm (2.47 eV) and a band- gap (band edge) of 1.89 eV. Upon doping (FeCl3) the polymer film becom es light blue-green and has a conductivity of 60 S cm(-1). The origina l absorption peak at 503 nm decreases, while two new near-IR absorptio ns at 860 and 1860 nm appear during doping, which is reversible. Quant um mechanical calculations show a rather low rotational barrier in the monomer, and additional calculations on various oligomers and the pol ymer suggest that the stable form of the polymer is aromatic and plana r.