Theoretical studies on the nonlinear optical properties of zwitterionic organic molecules: effect of π–σ–π through-bond coupling on the first hyperpolarizability

First hyperpolarizabilities (β) have been calculated by time-dependent Hartree–Fock (TDHF) formalism using the ab initio SCF wavefunctions for some zwitterionic organic molecules containing a π-electron donor and π-electron acceptor separated by saturated C–C σ-bonds (saturated bridges). The geometries of the molecules have been optimized using HF/6-31G basis sets. Charge transfer is observed even when the donor and acceptor are separated by more than one σ-bond, giving rise to a large first hyperpolarizability. This study suggests that these bridges may have potential applications in the development of nonlinear optical materials.