Designing hybrid materials with advanced optical properties using superalkali M3O (M = Li, Na, and K) and isoelectronic species of cyclo[18]carbon (B6C6N6 and B9N9)

Abstract

The geometric, electronic, and optical properties of the hybrid materials formed by complexing B6C6N6 and B9N9 with superalkali M3O (M = Li, Na, and K), that is, M3O@B6C6N6 and M3O@B9N9 (M = Li, Na, and K), were studied systematically by using (time-dependent) density functional theory [(TD-)DFT] and wavefunction analysis. The structure of B6C6N6 and B9N9 in the complexes exhibits varying degrees of deformation under the influence of M3O (M = Li, Na, and K). Natural population analysis (NPA) confirms charge transfer from the M3O (M = Li, Na, and K) to B6C6N6 and B9N9, and independent gradient model based on Hirshfeld partition (IGMH) analysis reveals the binding nature of the units. M3O@B6C6N6 (M = Li, Na, and K) series complexes exhibit higher polarizabilities (αiso) than M3O@B9N9 (M = Li, Na, and K) series, and K3O@B6C6N6 and K3O@B9N9 have the highest first hyperpolarizabilities (βtot) in their respective series, comparable to that of the corresponding complex of cyclo[18]carbon (C18). The M3O@B6C6N6 (M = Li, Na, and K) system remains almost transparent in the visible (Vis) region, but the absorption of M3O@B9N9 (M = Li, Na, and K) gradually covers the Vis region with the increase of alkali metal index. These results collectively demonstrate that complexing superalkali with molecular rings represents an effective strategy for designing high-performance nonlinear optical (NLO) materials, and K3O@B6C6N6 is an excellent candidate for Vis NLO molecule.