Determination of first-order molecular hyperpolarizability of EAADCy and EDMAADCy using steady-state spectroscopic data and quantum-chemical calculations

Ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) and ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate (EDMAADCy) organic molecules containing separate electron donor and electron acceptor groups belong to biphenyl derivatives in which a large dipole moment change between ground (S0) and the first intramolecular charge transfer excited (S1) states, as well as a large transition moment have been noted. The existence of electronically excited states with a strong intermolecular charge transfer (ICT) character is an essential prerequisite for large non-linear optical properties. Therefore, in this paper, we present a scrupulous analysis of the first-order hyperpolarizabilities of the studied molecules using an equivalent internal field model of an organic molecule. The calculated (using semiempirical calculations, CAChe WS 5.04) additive part of the first-order hyperpolarizability, βadd, values are discussed in relationship to the experimental data of the charge transfer hyperpolarizability, βCT, obtained from steady-state spectroscopic measurements.