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<sup>–</sup>+M<sup>2+</sup>(Ni@Pb<sub>12</sub>)<sup>2–</sup>M<sup>2+</sup>+e<sup>–</sup> (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 (<i>F</i>) hardly changes the molecular structure of the all-metal electrides, it seriously deforms their excess electron orbitals and average static first hyperpolarizabilities (β<sub>0</sub><sup>e</sup>(<i>F</i>)). For e<sup>–</sup>+Ca<sup>2+</sup>(Ni@Pb<sub>12</sub>)<sup>2–</sup>Ca<sup>2+</sup>+e<sup>–</sup>, a small external electric field <i>F</i> = 8 × 10<sup>–4</sup> 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@Pb<sub>12</sub>)<sup>2–</sup> 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 Ca<sup>2+</sup>(Ni@Pb<sub>12</sub>)<sup>2–</sup>Ca<sup>2+</sup>+2e<sup>–</sup>. Therefore, the small external electric field induces a dramatic β<sub>0</sub><sup>e</sup>(<i>F</i>) contrast from 0 (off form) to 2.2 × 10<sup>6</sup> au (on form) in all-metal electride molecule Ca­(Ni@Pb<sub>12</sub>)­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.