DESIGN OF NOVEL DONOR-ACCEPTOR POLYMERS WITH LOW BANDGAPS

Quantum chemical results on the electronic and geometric structures of some novel donor-acceptor polymers containing alternating electron-do nating group X (X = CH2, SiH2 or GeH2) and electron-accepting group Y (Y = drop C = CH2, = drop C = O, = drop C = CF2 or C = C(CN)(2)) along the conjugated cis-polyacetylene backbone, obtained on the basis of t he one-dimensional tight-binding self-consistent field-crystal orbital (SCF-CO) method at the MNDO-AM1 level of approximation, are reported. The optimized geometries of the polymers show a strong dependence on the nature of the electron-donating group X. Polymers derived from X = CH2 or GeH2 and Y = drop C = C(CN)(2) are predicted to have bandgap v alues of less than 1 eV. An analysis of their pi-bond order data and t he patterns of their frontier orbitals shows these two polymers to hav e quinoid-like electronic structures, in contrast to the benzenoid-lik e electronic structures for the rest of the polymers.