An External Electric Field Manipulated Second-Order Nonlinear Optical Switch of an Electride Molecule: A Long-Range Electron Transfer Forms a Lone Excess Electron Pair and Quenches Singlet Diradical

Abstract

An electride molecule e–···K­(1)+···calix­[4]­pyrrole···K­(2)+···e– as an external electric field (F) manipulated nonlinear optical (NLO) switch is designed theoretically for the first time. As this molecule is an unusual singlet diradical electride molecule with two easily driven excess electrons (by electric field) at two opposite ends of the molecule, a novel switching mechanism of electronic structure isomerization emerges as a distinctive nonbonding evolution in the electride molecule. A small electric field driving leads to a long-range excess electron transfer from one side K(1) through the middle calix[4]­pyrrole to the other side K(2), forms a lone excess electron pair of s-type rather than a single bond, and quenches the singlet diradical. Meanwhile, the molecular electronic structure becomes K(1)+···calix­[4]­pyrrole···K­(2)+···2e–. Therefore, the small electric field driving brings a very high static first hyperpolarizability (β0) contrast from 0 (F = 0, Off form) to 4.060 × 105 au (F = a small nonzero value of 5 × 10–4 au, On form). Notably, under the electric field of 30 × 10–4 au, β0 reaches the largest value of 3.147 × 106 au and the molecule displays the most optimal NLO switching behavior. Furthermore, we consider also that 4H atoms of calix[4]­pyrrole are substituted with 4F and 2Be atoms, respectively; then the 2Be and 4F substitution effects on the NLO switch in electride molecules are exhibited. This work opens a new research field of an electric field manipulated NLO switch of electride molecules.

A nonlinear optical switch induced by an external electric field: inorganic alkaline–earth alkalide

“…(EEF ¼ 30 Â 10 À4 (a.u. )), as well as Be 6 Li 8 and Be 6 Li 14 , were reported by Li and Hou et al 19,20,50 It is worth noticing that the above-mentioned NLO molecular switches are all electride molecules. 19,20,50 To the best of our knowledge, NLO switch molecules of an inorganic alkalineearth alkalide have not been reported yet.…”

“…Excess electron compounds have been proven to serve as potential candidates for NLO materials with excellent NLO responses. [15][16][17][18][19][20] In recent years, studies on excess electron compounds have gained plentiful attention. [21][22][23][24][25][26][27][28][29] Alkalides and electrides are typical representatives of excess electron compounds, where anion sites are occupied by anionic alkalis and trapped electrons, respectively.…”

“…light irradiation, 47 redox reaction, 48 pH variation, ion recognition, 49 external electric eld (EEF), and so on. 19,20,50 On the one hand, among the above-mentioned external stimulators, EEF plays an important role in chemistry. For instance, Nakano et al have shown that singlet diradical molecules induced by EEF can produce giant static second hyperpolarizability.…”

“…54 Furthermore, EEF is also used to probe other properties, such as the P stacking interaction, 55 proton transfer, 56 metal-ligand bonding, chemical reactions etc. 57 On the other hand, NLO switches with a large difference in NLO properties in the presence of external stimulator triggering have attracted more and more attention in recent years, 19,20,50 because of their excellent potential applications in signal processing, data storage and optical frequency converters etc. [3][4][5][6][7][8][9] In the presence of EEF triggering, NLO switches of the organic electride molecule K(1)/calix [4]pyrrole/K(2) with b e 0 values ranging from 0 (EEF ¼ 0 (a.u.))…”

Diradical Character and Second Hyperpolarizability of Alkaline Earth Metal Inverse Sandwich Complexes Involving Cyclopentadienyl and Cyclooctatetraene Ligands

“…Indeed, Liu et al reported that AISC systems with Ca as an alkaline earth metal shows intermediate diradical character ( y ) of sσ‐orbital of Ca atom . As the second‐order NLO materials, the similar structures of AISCs, like the alkali metal inverse sandwich molecules and all‐metal electrode molecules with the structure, in which the alkaline earth metals sandwich metal clusters, exhibit large first hyperpolarizabilities (the molecular‐level origin of 2 nd ‐order NLO properties) and act as external‐field‐induced NLO switch. Krieck et al have synthesized AISCs with Ca as an alkaline earth metal , .…”