Tin Metal Cluster Compounds as New Third-Order Nonlinear Optical Materials by Computational Study

It is quite appealing but challenging to predict and synthesize new nonlinear optical (NLO) materials with exceptional performance. Herein, the different Sn 4 cluster core structures and third-order NLO properties are studied through electronic structure, excited hole–electron, bonding character, and aromaticity analysis. As a result, Sn 4 clusters with ring core structure (Sn 4 -R) not only have the smallest E gap, the largest UV–vis response intensity, but also the strongest third-order NLO response in our work. As proved by natural bond orbitals’ (NBO) analysis, electron localization function (ELF), and adaptive natural density partitioning (AdNDP), the Sn 4 4+ has two in-plane four center-two electron (4c-2e) Sn–Sn σ-bonds, resulting in a good delocalization. For the first time, delocalization of metal cluster cores in tin clusters that is beneficial to the third-order NLO response is proposed, which provides a new guidance to design and prepare third-order NLO materials.