Electronic and nuclear contributions to the third-order optical susceptibility of the C 60-TTF dyads

Abstract

We have measured the third-order susceptibility χ ijkl 〈3〉 of a C 60-TTF compounds in tetrahydrofuran (THF) solutions using the degenerate four wave mixing technique at λ=532 nm in the picosecond regime. To know the physical nature of the optical non-linearities, we separate the electronic and nuclear contributions in χ 〈3〉. From these measurements we have deduced the values of the second-order hyperpolarisabilities γ. For the calculation of the susceptibility values, CS 2 has been used a reference material (having χ 〈3〉=1.24×10 −20 m 2 V −2) in a standard commonly used procedure taking into account the linear absorption of the sample. As the absorption of the studied compounds is very weak at λ=532. This paper presents a theoretical analysis of the second-order hyperpolarisabilities γ t of fullerenes modified, too. Theoretical calculations of the γ were carried out at the restricted Hartree–Fock level (RHF) using AM1 and PM3 semi-empirical SCF-MO methods within the HyperChem 7.0 program.