Band-gap engineering of donor-acceptor conjugated polymers

Three series of alternating donor-acceptor substituted co-oligomers (with different chain length), consisting of pyrrole or thiophene as the electron-rich unit and quinoxaline or 2,1,3,-benzobisthiadiazoles as the electron-deficient unit, were prepd. by Pd-catalyzed Stille coupling methodol. The incremental bathochromic shift of the absorption max. upon chain elongation of the three series of oligomers is less than that of the homo-oligomers of thiophene and pyrrole, which is caused by a diminished dispersion of the LUMO level upon chain elongation. The latter conclusion was drawn after comparing the oxidn.- and redn. behavior of the thiophene/benzothiadiazole oligomers with that of thiophene oligomers. The incremental bathochromic shift shows similarity for all three series of oligomers, which is used as a tool in the band-gap engineering of donor-acceptor substituted conjugated polymers