Comparative photophysics and ultrafast dynamics of dimethylaminochalcone and a structurally rigid derivative: experimental identification of TICT coordinate.

Photophysical parameters and ultrafast dynamics of dimethylaminochalone (DMAC-A) have been compared with a structurally bridged analogue (namely, c-DMAC) in solvents of varying polarities. Conformational locking of the single bond connecting the donor and acceptor groups in c-DMAC arrests the twisted intramolecular charge transfer (TICT) relaxation and consequently the photophysical parameters such as fluorescence yield, fluorescence lifetime and triplet yield change significantly. The intramolecular charge transfer character of the LE state is found to be unaffected by conformational restriction. Femtosecond transient absorption spectroscopic studies confirmed that in polar solvents, solvation is the only relaxation process in c-DMAC as opposed to the ultrafast TICT of DMAC-A. The solvent polarity effect on the relaxation dynamics has also been discussed.