Solvatochromism and intramolecular charge transfer in dialkylamino-substituted halogenated thienyl chalcone analogues

Abstract

Herein, we present the study of two complementary intramolecular charge transfer (ICT) transitions in two sets of dialkylamino-substituted halogenated thienyl chalcones. We demonstrate that while the first (and stronger) ICT takes place from the 4-(dialkylamino)phenyl moiety to the enone, the second ICT involves the thienyl substituent as the donor. The former is evidenced by a robust solvatochromic shift in both absorption and emission spectra, implying a large increase in the dipole moment upon excitation to the lowest excited state. The latter, a short-range ICT process, is confirmed upon photoexcitation of the higher energy bands, and its enhancement by the larger polarizability of the iodine substituent. With the help of (TD)-DFT calculations and the solvatochromic method, we quantified the extent of these effects and set the stage for further developments towards the design of new chalcone-based dyes. We demonstrated that theoretical calculations allow fine-tuning the sensitive balance between these complementary ICT processes.