Nonlinear optical properties and performance optimization of the pro-aromatic chromophores for NLO materials

Geometric structures and nonlinear optical properties (NLO) of the pro-aromatic chromophores, comprising indoline moiety as an electron donor and azo linker as a π-conjugated bridge, have been investigated by means of quantum chemistry method and the response theory. Three solvent models were used to study the short-range interaction and long-range interaction between solvent and solution in order to simulate the experimental spectra. Simulated absorption used by the polarizable continuum model gave a well agreement with experimental measurement. The micro-mechanisms of first hyperpolarizability were explained on the basis of the two-level models, and charge difference density methods demonstrated that the chromophore (4f), which indoline moiety acts as an electron donor and N,N-dimethyl formamide as an acceptor bridged by azo bridge, displays an efficient intramolecular charge transfer properties amplifying the NLO response. Calculations of two-photon absorption (TPA) for the indoline chromophore were performed to develop their potential application on TPA materials. Additionally, some molecules were designed by replacing electron donor and introducing additional heteroatoms to tune the NLO parameters. The results show 4f-a with 1,4-phenylenediamine donor unit and introducing one heteroatom display well NLO character.