External electric field driven conformation transition between lithium salts and electride-like molecules: intriguing NLO switches in Li@corannulene

Abstract

The external electric field has emerged as a powerful tool for building molecular switches with excellent properties. In this work, we investigate the impact of an external electric field on the transition between lithium salt and electride-like molecule conformations in Li@corannulene. Remarkably, the distance between the Li atom and the corannulene bottom displays a sharp increase under the influence of an external electric field strength of F_−z = 110 × 10⁻⁴ a.u. As the external electric field strength increases, the Li atom brings about different directions of charge transfer (CT). The natural population analysis (NPA) charge and the molecular electrostatic potential (ESP) results show that the intermolecular CT occurs from the Li atom to the corannulene with the F_−z ranging from 0 to 100 × 10⁻⁴ a.u. Interestingly, when the external electric field reaches F_−z = 110 × 10⁻⁴ a.u., the CT is oriented from the corannulene to the Li atom. Moreover, electron localization function (ELF) basins are presented under an F_−z of 110 × 10⁻⁴ a.u., which indicates that Li@corannulene exhibits electride-like (e⁻⋯[Li@corannulene]⁺) molecules and lithiation salt (Li⁺[corannulene]⁻) under an F_−z of 0 to 100 × 10⁻⁴ a.u. Significantly, the differences in charge transfer also contribute to a significant improvement in hyperpolarizabilities (β_tot) during the conformation transition from lithiation salt (Li⁺[corannulene]⁻) to electride-like (e⁻⋯[Li@corannulene]⁺) molecules. This study explores the potential of Li@corannulene as a promising second-order NLO material, and the external electric field provides an efficient strategy for designing and developing NLO switching devices.