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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

He, Hui-Min, Li, Ying, Yang, Hui, Yu, Dan, Li, Si-Yi, Wu, Di, Hou, Jian-Hua, Zhong, Rong-Lin, Zhou, Zhong-Jun, Gu, Feng-Long, Luis, Josep M., Li, Zhi-Ru
The Journal of Physical Chemistry C 2017 v.121 no.1 pp. 958-968
calcium, chemical structure, electric field, electron transfer, electrons, isomerization, magnesium
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 (β₀ᵉ(F)). For e–+Ca²⁺(Ni@Pb₁₂)²–Ca²⁺+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 β₀ᵉ(F) contrast from 0 (off form) to 2.2 × 10⁶ au (on form) in all-metal 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.