Shedding light on static and dynamic hyperpolarizabilities of thia[7&8]circulenes, toward their NLO applications

Herein, we examined the nonlinear optical properties of thia[7&8]circulenes (1-18). Circulenes are the building blocks of various nanomaterials such as graphene, nanotubes, and fullerenes. Many studies on circulenes have focused on the aromaticity of circulenes, but less attention has been paid on optoelectronics properties. Carbon atoms of the [7&8]circulenes are replaced with multiple sulfur atoms to designed thia[7&8]circulenes (1-18). These circulenes (1-18) are thermodynamically, kinetically, and chemically stable. Nonlinear optical (NLO) response is evaluated through static and frequency-dependent first and second hyperpolarizability values. The static first hyperpolarizability (β_o) of these compounds ranges between 0.00 and 496 au. The frequency-dependent coefficients for all thia[7&8]circulenes show remarkable enhancement at 532 and 1064 nm, respectively. The nonlinear refractive index is increased up to 1.13 × 10^-14 au for circulene 9 at 532 nm. These findings successfully demonstrated that nonlinear optical response of thia[7&8]circulenes can be increased by decorating multiple sulfur atoms. The unsymmetrical distribution of sulfur atoms is more effective in enhancing nonlinear optical response.