Efficient external electric field manipulated nonlinear optical switches of all-metal electride molecules with infrared transparency: Nonbonding electron transfer forms an excess electron lone pair

Focusing on the interesting new concept of all-metal electride, centrosymmetric molecules e^-+M²⁺(Ni@Pb₁₂)^2-M²⁺_+e^- (M = Be, Mg, and Ca) with two anionic excess electrons located at the opposite ends of the molecule are obtained theoretically. These novel molecular all-metal electrides can act as infrared (IR) nonlinear optical (NLO) switches. Whereas the external electric field (F) hardly changes the molecular structure of the all-metal electrides, it seriously deforms their excess electron orbitals and average static first hyperpolarizabilities (β^e₀ (F)). For e^-+M²⁺(Ni@Pb₁₂)^2-M²⁺_+e^-, a small external electric field F = 8 × 10^-4 au (0.04 V/Å) drives a long-range excess electron transfer from one end of the molecule through the middle all-metal anion cage (Ni@Pb₁₂)^2- to the other end. This long-range electron transfer is shown by a prominent change of excess electron orbital from double lobes to single lobe, which forms an excess electron lone pair and electronic structure Ca²⁺(Ni@Pb₁₂)^2-Ca²⁺+2e^-. Therefore, the small external electric field induces a dramatic β^e₀ (F) contrast from 0 (off form) to 2.2 × 10⁶ au (on form) in allmetal electride molecule Ca(Ni@Pb₁₂)Ca. Obviously, such switching is high sensitive. Interestingly, in the switching process, such long-range excess electron transfer does not alter the valence and chemical bond nature. Then, this switching mechanism is a distinct nonbonding evolution named electronic structure isomerization, which means that such switching has the advantages of being fast and reversible. Besides, these all-metal electride molecules also have a rare IR transparent characteristic (1.5-10 μm) in NLO electride molecules, and hence are commendable molecular IR NLO switches. Therefore, this work opens a new research field of electric field manipulated IR NLO switches of molecular all-metal electrides.