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

Abstract

An intriguing class of excess electron compounds with unique electronic structures was obtained on the basis of a facially polarized molecule, namely, 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 first constructed. The calculated results show that unlike 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, thus forming an alkali metal anion, while the remaining 4s electron of Ca is pushed away from Ca⁺, yielding localized electrons around it by the instinctive facial polarization of 1 or with the assistance of oriented external electric fields (OEEFs). Interestingly, these novel compounds exhibit extremely large first hyperpolarizabilities (β₀) in the range of 9.94 × 10⁵–1.81 × 10⁶ a.u. and high stability. Thus, this work can provide first members simultaneously containing typical alkalide features and electride-like characteristics to further enrich the family of excess electron compounds and offer novel candidates for NLO materials with high performance.