An MP2 study of linear polarizabilities and second-order hyperpolarizabilities for centrosymmetric squaraines

The ground-state geometry, basis set, electron correlation, and frequency dependency of the longitudinal components of linear polarizabilities αzz and second hyperpolarizabilities γzzzz of the centrosymmetric (2,4-diphenyl)squaraine and its derivatives have been studied using finite-field (FF) and time-dependent Hartree–Fork (TDHF) approaches, respectively. The substitution at the para and/or ortho positions at the phenyl rings is crucial to the magnitude and sign of γzzzz, depending on the nature of the substituents. Going from powerful electron-withdrawing groups to powerful electron-donating groups at para positions, γzzzz varies from positive to negative, while the ortho hydroxys at the phenyls enhance greatly the negative γzzzz values. The computational methodology affects considerably the calculated γzzzz values, especially for the squaraines with weak donors at both terminals.