Designing a new class of excess electron compounds with unique electronic structures and extremely large nonlinear optical responses

An intriguing type of excess electron compounds with unique electronic structures was achieved on the basis of a facially polarized molecule all-cis 1,2,3,4,5,6-hexafluorocyclohexane (1). By doping two different faces of this Janus molecule with an alkaline earth atom and an alkali-metal atom, a series of M-1-M' (M = Be, Mg, and Ca; M' = Li, Na, and K) compounds were firstly constructed. Calculated results show that, different from Be and Mg, one 4s electron of Ca in Ca+-1-M'− (M' = Li, Na, and K) can be transferred to the upper alkali metal atom forming an alkali metal anion, while the remaining 4s electron of Ca was pushed away from Ca+ yielding localized electrons around it by the instinctive facial polarization of 1 or with the assist of oriented external electric fields (OEEFs). More interesting, these novel compounds exhibit extremely large first hyperpolarizabilities (β0) of 9.94 × 105‒1.81 × 106 au and high stability. Thus, this work could provide the first members simultaneously containing typical alkalide features and electride-like characteristics to further enrich the family of excess electron compounds and offer novel candidates as NLO materials of high performance.