Third order NLO properties of corannulene and its Li-doped dimers: effect of concave–convex and convex–convex structures

Abstract

Buckybowls involving π–π interactions offer exciting future opportunities in terms of designing novel smart nonlinear optical (NLO) materials. Dimeric species of corannulene (C₂₀H₁₀), the smallest buckybowl, was considered as a model for the host–guest assemblies, which exhibited the convex–concave stacking of curved conjugated carbon surfaces. Different stacking motifs (concave–convex and convex–convex dimers) of C₂₀H₁₀ dimers that affect the NLO properties are the focus of our study. We performed density functional theory calculations on the structure, binding interactions, electronic absorption spectra and second hyperpolarizabilities of π-stacking dimers of C₂₀H₁₀ and its Li-doped derivative. It was found that the concave–convex dimers exhibit stronger binding interactions because of larger electrostatic interactions and thus are more stable with respect to the convex–convex dimers. The doping of Li ion significantly enhances the orbital interaction between the monomers but slightly affects the spectra and the second hyperpolarizabilities of the dimers. The convex–convex dimers exhibit larger polarizabilities and second hyperpolarizabilities (γ_zzzz) as a result of enhanced interlayer charge transfer properties. There is an increasing linear relationship between the electronic coupling and γ_zzzz values. The results presented in this article provide important evidence for the convex–convex stacking motif that enhances the NLO properties of the π-stacking dimers. Thus, controlling molecular stacking is an important way in terms of designing novel smart NLO materials.