Major intermolecular effects on nonlinear electrical response in a hexatriene model of solid state polyacetylene

Through detailed model studies, benchmarked by extensive ab initio calculations, we show (1) how sizable medium effects on molecular electrical response of polymeric solids can arise; (2) that classical electrostatics accurately reproduces a full quantum treatment; and (3) that for a large bundle of hexatriene molecules taken as a model of polyacetylene, the medium effect will lead to as much as a 95% reduction in the second hyperpolarizability and a 50% reduction in the polarizability. For designing organic materials with enhanced nonlinear optical (NLO) properties, the results reveal features that might be optimized and point to a sound model for selecting other features.