Theoretical study of the first-order and third-order polarizabilities in benzene and thiophene derivatives: Influence of ethenyl derivation and quinoid geometries

We present ab initio Coupled Perturbed Hartree-Fock calculations on the first-order and third-order polarizabilities of several benzene and thiophene derivatives in either aromatic or quinoid geometric structures. As the calculated optical nonlinearities are known to be very sensitive to the size and nature of the basis set used for the calculations, we first examine the efficiency of different basis sets including polarization and diffuse functions. The 3-21 G+pd basis set appears to be appropriate to calculate the third-order polarizabilities in the organic molecules considered in this work. We then analyze the influence on the nonlinear optical components of the introduction on the aromatic ring of an ethenyl group, as well as the effect of a switch to a quinoid structure. The results confirm an important increase in the γ values when derivatizing the aromatic rings with an ethenyl group. However, the switch from an arylethenyl type of structure to a purely quinoid structure does not lead to any significant increase in the average γ value.