Inverse photoinduced electron transfer in large betaine molecules

We have used ab initio methods to confirm the existence of an inversion in the photoinduced intramolecular electron transfer in large conjugated pyridinium betaines, by examining compounds where an imidazole ring and a pyridinic group are connected by polyenic chains of increasing size. As these intermediary conjugated bridges get longer, an unusual net charge transfer is observed. The conjugated chain becomes a channel for the photoinduced electronic density flow, and the amount of charge at the donor and acceptor groups is reduced, while an inversion in the spatial localization of the frontier orbitals occurs. We discuss the corresponding implications on the nonlinear optical, photochemical and solvatochromic properties of these molecules.

Ab initio methods were used to confirm the existence of an inversion in the direction of the photoinduced intramolecular electron transfer in large conjugated pyridinium betaines. We have examined a family of compounds where an imidazole and a pyridinic group are connected by polyenic chains of increasing size. For longer intermediary conjugated bridges, an unusual net charge transfer is observed, as the photoinduced electronic flow happens from the acceptor side to the donor moiety of the molecule. We discuss the implications of the observed inversion of the spatial localization of the frontier molecular orbitals upon the nonlinear optical, photochemical and solvatochromic properties of these molecules.