Towards organic polymers with small intrinsic band gaps. II. Investigation of the electronic structure of poly(pyrenylene vinylenes)

Geometry optimizations and band structure calculations are reported on two polymeric vinylene derivatives of pyrene: poly(1,6-pyrenylene vinylene) and poly(2,7-pyrenylene vinylene). The results are indicative of a dramatic sensitivity of the electronic structure on the mode of connection of the two vinylene units to the pyrene rings, in agreement with the chemist's intuition. An analysis of the atomic π orbital contributions to the one-electron wave functions shows that the HOMO-LUMO characteristics of both compounds are markedly different. The 1-6 mode of connection leads to an electronic structure similar to that of polyparaphenylene with a bandgap of 2.9 eV. The 2-7 mode of connection results in a significantly lower bandgap, around 1.7 eV, due to the stabilization of quinoid resonance structures.