Sensing mechanism of a ratiometric near-infrared fluorescent chemosensor for cysteine hydropersulfide: Intramolecular charge transfer

Previous studies have shown that the cysteine hydropersulfide (Cys-SSH) as the sulfur donor is crucial to sulfur-containing cofactors synthesis. Recently, a selective and sensitive near-infrared ratiometric fluorescent chemosensor Cy-DiSe has been designed and synthesized to detect Cys-SSH spontaneously. Herein, by means of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches, the sensing mechanism has been thoroughly explored. According to our calculations, the experimental data have been reproduced. The results indicate the intramolecular charge transfer (ICT) is the reason for changes in fluorescence wavelengths. Compared with the chemosensor Cy-DiSe, the larger energy gap of Cy induced by ICT mechanism leads to the blue-shift of the absorption and emission spectra, which guarantees that Cy-DiSe can become a ratiometric fluorescent chemosensor to detect Cys-SSH.