Novel inorganic aromatic mixed-valent superalkali electride CaN3Ca: an alkaline-earth-based high-sensitivity multi-state nonlinear optical molecular switch

Focusing on innovative high-performance single-pole double-throw nonlinear optical (NLO) molecular switches, two C-3v configurations (1 and 3) and one D-3h configuration (2) of bipyramidal CaN3Ca have been obtained by using quantum mechanical methods. Not only are 1, 2, and 3 alkaline-earth-based aromatic superalkalis, but they are also interesting electrides. The salt-like electronic structures of e(-)MIDLINE HORIZONTAL ELLIPSISCa2+N33-Ca2+ (1) and Ca2+N33-Ca2+MIDLINE HORIZONTAL ELLIPSISe- (3) with localized redox centres are rare inorganic Robin-Day class II-type structures, and e(0.5-)MIDLINE HORIZONTAL ELLIPSISCa2+N33-Ca2+MIDLINE HORIZONTAL ELLIPSISe0.5- (2) with a delocalized structure is a class III-type mixed-valent superalkali electride. Under a small external electric field of +/- 0.0110 a.u. (0.565 V angstrom(-1)), the short-distance hopping of Ca atoms in CaN3Ca from the D-3h configuration with in-plane aromaticity to each C-3v configuration with out-of-plane aromaticity brings about the long-range transfer of half an electron from one Ca atom to another. And, subsequently, a large dipole moment (mu(0)) and remarkable static first hyperpolarizability (beta(0)) occur. mu(z) and beta(zzz) range from 0 (D-3h, off form) to -12.1 or 12.1 D (C-3v, on forms) and from 0 (D-3h, off form) to -19 428 or 19 428 a.u. (C-3v, on forms), respectively. These extremely large differences in mu(z) and beta(zzz) values between the D-3h and each of the C-3v configurations confirm the potential of these inorganic aromatic Robin-Day-type superalkali electrides for applications in high-sensitivity multi-state nonlinear optical switches.