Effects of the Cage Number and Excess Electron Number on the Second Order Nonlinear Optical Response in Molecular All-Metal Electride Multicage Chains

Abstract

For novel all-metal electride, multicage chain structures [(Ni@ Ge 9 ) Ca 3 ] n (n = 1−4) with all real frequencies are obtained theoretically for the first time. In the structure of n = 1, the Ni@Ge 9 metal cage as the shortest chain skeleton is surrounded by nonbridge Ca atoms. In the structures of n = 2−4, Ni@Ge 9 metal cages are connected by bridge Ca atom pair(s) forming new hybrid multicage chain skeletons surrounded by nonbridge Ca atoms. And interesting pull−push electron relay occurs. The chain skeleton pulls valence electrons from nonbridge Ca atoms forming skeleton polyanion, and then formed polyanion pushes remaining valence electrons of the Ca atoms forming excess electrons. The excess electron numbers are Ne = 2, 0, 4, 4 for n = 1, 2, 3, 4, respectively. It is shown that these structures with excess electrons are molecular all-metal electride multicage chains, unexpectedly, and the structure (n = 2) without excess electron is a Ca salt. For nonlinear optical (NLO) response, the electride chains have large static first hyperpolarizabilities (β 0 e ). And β 0 e increases strongly from 9321 (n = 1, N e = 2) to 54232 au (n = N e = 4), which exhibits that significant cage number and excess electron number effects on NLO response. Besides electronic contribution (β 0 e ) to static first hyperpolarizability, the large vibrational contribution (β 0 nr ) are also revealed, and the ratios of β 0 nr /β 0 e are 0.18−1.17. Moreover, the frequency-dependent values β e (−2ω; ω, ω) and β e (−ω; ω, 0) have also been estimated. Especially, the evolutions of prominent cage number effects on β 0 e , β 0 nr , β e (−2ω; ω, ω) and β e (−ω; ω, 0) are similar. Then a new design strategy of enhancing NLO response by increasing metalcage number is obtained. Hence, these molecular all-metal electride multicage chains as novel nanorods are promising new NLO nanomaterials.

Nonlinear optical response of endohedral all-metal electride cages 2e−Mg2+(M@E12)2−Ca2+(M = Ni, Pd, and Pt; E = Ge, Sn, and Pb)

“…The VIP correlates with the size of the spherical lobe rounding Mg in HOMO, which is associated to the dispersion of excess electron density. The VIP values of these molecules are slightly larger than the reported values of inorganic, organic and other all-metal electride molecules,15,24,30,31,56 but smaller than the very larger value (7.78 eV) of the electride molecule with the excess electron protected inside the C 36 F 36 cage.…”

“…30 Moreover, we also constructed one-dimensional all-metal electride chains [(Ni@Ge 9 )Ca 3 ] n (1, 2, 3, and 4) and explored their structures and electric properties. 31 In this all-metal electride multicage chain series, increases strongly from 9321 (n = 1, N e = 2) to 54232 au (n = N e = 4),…”

Germanium-based superatom clusters as excess electron compounds with significant static and dynamic NLO response; a DFT study

“…14 The excess electron system is well-known for triggering second and third-order nonlinearity. 15,16 In the family of excess electron compounds, electride, 17 alkalides, 18 and alkalineearthides 19,20 are well known.…”

Substituent effects at nitrogen/phosphorus atoms of dialkaline earth metal complexes: Excess electron and large second‐hyperpolarizability

“…Other useful strategies have been made to consider different species with varying shapes, sizes, a number of coordination sites, number of excess electrons along with their different spin states to optimize the magnitude of first‐hyperpolarizability. However, first‐hyperpolarizability of diffuse electron compounds has been studied widely than the second‐hyperpolarizability.…”