Third-order nonlinear optical properties of the host–guest complexes formed between fullerenes and cycloparaphenylene ([n]CPP: n = 9, 10 and 11)

Abstract

The host–guest complexes formed between [9–11]CPPs and C₆₀ were studied extensively due to their excellent photoelectric conversion properties and photochemistry. The drastically increased electron accepting ability of Li⁺@C₆₀ with respect to C₆₀ may induce strong intermolecular charge transfer interaction with [9–11]CPP. In this paper, a comprehensive computational analysis of the structure, intermolecular interactions, absorption spectra, charge transfer characteristics and nonlinear optical properties of [9–11]CPP⊂C₆₀ and [9–11]CPP⊂Li⁺@C₆₀ were studied using density functional theory calculations. It was found that the intermolecular binding energies of [10]CPP⊂C₆₀ and [10]CPP⊂Li⁺@C₆₀ were −47.76 and −60.08 kcal mol⁻¹, which were larger than those of [9, 11]CPP⊂C₆₀ and [9, 11]CPP⊂Li⁺@C₆₀. Thus, [10]CPP was found to be the most ideal fullerene encapsulator and most suitable for encapsulating C₆₀. In addition, with the increase of the CPP ring size, the second hyperpolarizability (γ) values of [n]CPP⊂C₆₀ increase gradually. In addition, the γ values of [9–11]CPP⊂Li⁺@C₆₀ were all greater than those of [9–11]CPP⊂C₆₀, indicating that embedding Li⁺ into fullerene spheres can effectively improve their third-order nonlinear optical responses.