Small band gap oligothieno[3,4-b]pyrazines

The synthesis and the optical and electrochemical properties of thiophene end capped oligo(2,3-alkylthieno3,4- b]pyrazine)s are presented. The optical absorption rapidly shifts to lower energies with increasing chain length, caused in almost equal amounts by a rise of the HOMO and a lowering of the LUMO levels. The optical band gap of the polymer is estimated to be 1.13 +/- 0.07 eV. Extrapolated redox potentials indicate that the polymer is a small band gap p-type material.