The effect of changes in pi-conjugated terthienyl systems using thienyl and ethylenedioxybenzene functionalized thieno[3,4-b]pyrazine precursors: Multicolored low band gap polymers

New classes of thieno[3,4-b]pyrazines containing thienyl and ethylenedioxy phenyl units on electron-withdrawing moieties of pi-conjugated terthienyl were synthesized. The effect of structural differences on electrochemical and optoelectronic properties of the resulting polymers was investigated. Changes in the electronic nature of the functional groups enable to tune the electrochemical properties of the pi-conjugated terthienyl monomers by lowering oxidation potential from 062 V (DTTP) to 056 V (DBTP) Spectroelectrochemical analyses revealed that the neutral polymer (PDBTP) is dark green in its neutral state revealing pi-pi* transitions in two well-separated bands at 410 and 751 nm The electronic band gap of polymer, defined as the onset of the pi-pi* transition, is found to be 1.0 eV Using the thienyl unit instead of ethylenedioxy phenyl, a red shift in the band gap (0 95 eV) is observed The polymer, PDTTP, exhibits multicolor electrochromism and can be switched between a dark yellow neutral state, a green intermediate state, and a brown oxidized state PDBTP also shows a multicolored electrochromic behavior with three distinct states: dark green at the neutral state, a brown intermediate state, and a brown-violet oxidized state. (C) 2010 Elsevier Ltd. All rights reserve