Long-Range Charge Transfer Driven by External Electric Field in Alkalides M–LCaL–M (M = Li or Na, L = All-cis 1,2,3,4,5,6-Hexafluorocyclohexane): Facially Polarized Janus-Type Second Order Nonlinear Molecular Optical Switches

Alkalides with large nonlinear optical (NLO) responses exhibit broad applications in the electro-optical device field. In the present work, based on alkali (Li and Na) in conjunction with alkaline-earth (Ca) atoms doped into facially polarized all-cis 1,2,3,4,5,6-hexafluorocyclohexane (C₆F₆H₆), we first reported two facially polarized Janus-type alkalides as an external electric field (EEF)-induced second order NLO switches M–LCaL–M (M = Li or Na, L = C₆F₆H₆). The two 4s electrons of the Ca atom are, respectively, pushed out by the negative fluorocarbon face of one L and each of them concentrate on one alkali atom and combine with the s electron of the later to form excess electron pair. Owing to the two excess electron pairs [highest occupied molecular orbital (HOMO) and HOMO – 1], the novel alkalides M^––LCa²⁺L–M^– is formed. Interestingly, with continuous increasing of EEF magnitude, the centrosymmetric M^––LCa²⁺L–M^– bearing two excess electron pairs is obviously broken and a long-range charge transfer is exhibited gradually from one end of the alkali atom through the middle LCaL to the other end of it. Meanwhile, the influence of EEF brings a large static electronic first hyperpolarizability from 0 (EEF = 0, off form) to 59 826 (M = Li, EEF = 19 × 10^–4 au, on form) or 64 231 au (M = Na, EEF = 12 × 10^–4 au, on form). They also have the largest vibrational first hyperpolarizabilities (on form). These results show that alkalides M^––LCa²⁺L–M^– have potential application for NLO materials as well as exhibit advantages such as high sensitivity, being fast, and having reversible switching.