Interplay between the diradical character and third-order nonlinear optical properties in fullerene systems

Abstract

To reveal new structure-property relationships in the nonlinear optical (NLO) properties of fullerenes that are associated with their open-shell character, we investigated the interplay between the diradical character (y i) and second hyperpolarizability (longitudinal component, γzzzz) in several fullerenes, including C20, C 26, C30, C36, C40, C42, C48, C60, and C70, by using the broken-symmetry density functional theory (DFT; LC-UBLYP (μ=0.33)/6-31G*//UB3LYP/6- 31G*). We found that the large differences between the geometry and topology of fullerenes have a significant effect on the diradical character of each fullerene. On the basis of their different diradical character, these fullerenes were categorized into three groups, that is, closed-shell (y i=0), intermediate open-shell (0