Theoretical study on second hyperpolarizability of pyridinium cation-chrolide anion pair: Structre-NLO-correlation of the ion pair

Static hyperpolarizability of pyridinium cation-chloride anion pair is investigated by ab initio molecular orbital (MO) method. It is found that the component of molecular second hyperpolarizability in the direction of cation-anion linkage drastically increases as the distance between the ion pair increases. This strong dependence of the second hyperpolarizability on the distance is considered to reflect the structure-NLO-correlation of organic ion systems.