Geometric structure and electronic properties of poly[2,3-8,9]benzanthracene, a new fully fused-ring conjugated polymer

We report modified neglect of diatomic overlap (MNDO) geometry optimizations and valence-effective Hamiltonian (VEH) band structure calculations on a new ladder-type polymer, poly[2,3-8,9]benzanthracene (PBA). Interest in this new fully fused-ring polymer arises from the fact that its synthesis has been recently achieved. The theoretical results indicate that both the geometric and electronic structures of PBA are to be interpreted as resulting from the interactions between a fully planar polyparaphenylene chain and the ethylenic moieties which bridge it. The VEH calculated bandgap for PBA is high, on the order of 2.86 eV, i.e., a value similar to the one calculated for planar polyparaphenylene itself. This wide bandgap is shown to arise from the [HOMO - 1] and [LUMO + 1] levels of polyparaphenylene, the former (latter) being destabilized (stabilized) by antibonding (bonding) interactions with the ethylenic moieties. Differences between linear and angular annelations are briefly discussed.