Theoretical design of donor-acceptor polymers with low bandgaps

The electronic and geometric structures of some novel hypothetical donor-acceptor polymers containing alternating electron-donating group X (X = CF2, SiF2, or GeF2) and electron-accepting group Y (Y = drop C=CH2, drop C=O, drop C=CF2 or drop C=C(CN)(2)) obtained on the basis of the one-dimensional tight-binding self-consistent field-crystal orbital (SCF-CO) method at the MNDO-AMI level of approximation are reported. Polymers derived from X = CF2, SiF2 or GeF2 and Y = drop C=C(CN)(2) are predicted to have stable quinoid-like electronic structures with bandgap values of less than 1 eV. All other polymers are found to have benzenoid-like electronic structures. The smaller bandgap values of the quinoid-like polymers in contrast to the benzenoid-like polymers are rationalized on the basis of their pi-bond order data and the patterns of their frontier orbitals. (C) 1998 Elsevier Science B.V.