Carbazole based NLOphoric styryl dyes- synthesis and study of photophysical properties by solvatochromism and viscosity sensitivity

We have synthesized push-pull chromophore based on carbazole moiety. The intramolecular charge transfer (ICT) of these dyes were examined by photophysical properties such as absorption, emission and fluorescence quantum yield in varying solvents of different polarities. They show absorption and emission in the range of 390-460 nm and 510-600 nm respectively. Oscillator strengths, transition dipole moments, different solvent polarity functions and frontier molecular orbital (FMO) analysis have been studied for understanding charge transfer from donor to the acceptor moiety. Density Functional Theory (DFT) revealed dyes with phenyl group in conjugation path with an acceptor (Dyes 9c and 10c) exhibited a relatively lower sigma(2PA) cross-section in comparison to their counterparts devoid of conjugation (Dyes 9a, 9b, 10a, and 10b). Viscosity induced emission intensity enhancement has been observed for all dyes at 0-100% PEG-400 in ethanol 9c and 10c are good FMR as compared to the other due to the presence of extra-p-conjugation. Bond length, bond order alternation analysis and non-linear polarizability studies of these dyes were calculated by DFT. The spectral variations were analyzed by means of linear solvation energy relationships concept proposed by Kamlet-Taft and Catalan parameters which indicate that solvent polarizability/dipolarity play an important role as compared to solvent acidity or basicity. Thus, linear and non-linear optical properties of styryls have been determined.