Twisted intramolecular charge transfer: A time-dependent density functional theory study on the sensing mechanism of a Schiff base sensor for fluoride

The fluoride-sensing mechanism of a Schiff-base type sensor (Dyes Pigments, 2015, 123, 166) has been investigated by time-dependent density functional theory. The experimental ultraviolet and fluorescence spectra of the sensor before and after fluoride addition were well reproduced. The theoretical results showed that sensor molecules had distinctly different geometries in the ground state and first singlet excited state, which corresponded with the proposed twisted intramolecular charge transfer process and explained how the sensor fluorescence quenched. Thus, the sensor analysis of the fluoride anion by fluorescent spectroscopy was explained.