Tuning the band gap of easily oxidized bis(2-thienyl)- and bis(2-(3,4-ethylenedioxythiophene))-phenylene polymers

The synthesis, characterization and electrochemical polymerization, along with redox switching behavior of the resultant polymers, of 1,4-bis(2-(3,4-ethylenedioxy)thienyl)-2,5-difluorobenzene (1) and 1,4-bis(2-thienyl)-2,5-difluorobenzene (2) is presented. Compounds 1 and 2 were synthesized by a Pd degrees-catalyzed cross-coupling and in good yields (85% and 84%, respectively). both monomers electropolymerize to form electroactive redox switchable films, with the more electron-rich 3,4-ethylenedioxythiophene derivative polymerizing and switching at lower potentials. The electronic band gaps were determined to be 1.9 eV for P1 and 2.3 eV for P2. Thin films of P1 and P2 were found to be electrochromic and exhibit color changes of red-to-blue/black for P1 and yellow-to-black for P2. These results are compared with various substituted bis(heterocycle)benzene derivatives in order to present a series of structure to property relationships. (C) 1998 John Wiley & Sons, Ltd.