Rotational Isomerism of Phenylthiolated Chromophores with Large Variation of Optical Nonlinearity

We design and synthesize various π-conjugated phenyltriene chromophores having different thiolated electron donor groups such as thiol, alkylthiol, and arylthiol groups to systematically investigate the electron-donating ability of sulfur analogues. For comparison, we also investigate the commonly used electron donor groups, oxygen-containing hydroxyl and alkoxy groups, as well as nitrogen-containing dialkylamino groups. Experimental and/or theoretical analysis of the nonlinear optical properties of these chromophores in gas, solution, and solid states suggest that the rotational isomerization of an arylthiolated group acting as electron donor in polyene chromophores induces a large variation of molecular optical nonlinearities. The first hyperpolarizabilities, calculated separately with finite-field (FF) and time-dependent density functional theory (TD-DFT) two-state model methods, indicate that this phenomenon is a consequence of the competitive electronic transitions from the ground state to the first and second excited states modulated by the rotation of thiophenyl group.