Theoretical study on the excited state mechanism of the fluorescent probe for detecting HOCl

Abstract

The abnormal level of hypochlorous acid (HOCl) in the human body will cause a series of diseases, and it is of great importance for designing and developing efficient fluorescent probes to detect HOCl. In this work, the fluorescence mechanism of BTMSP, a ratiometric fluorescent probe for detecting HOCl based on the sulfide oxidation reaction, has been studied through theoretical calculations. The optimized geometric configuration and infrared spectroscopy analysis of BTMSP and BTMTP at the ground state and excited state demonstrate that the intramolecular hydrogen bond interaction (O − H···N) strengthened, which will facilitate the proton transfer at the excited state. The potential energy curves for BTMSP and BTMTP at the S0, S1 state along the increasing in bond length of O–H were scanned. The frontier molecular orbitals (MOs) and charge density difference (CDD) map, the distribution of electrons and holes were discussed to investigate the charge transfer process. In addition, the calculated emission spectra demonstrates a significant blue shift in the wavelength occurred when BTMSP was oxidized by HOCl, which is consistent with the experimental results. All of the above calculated results indicate the excited state intramolecular proton transfer (ESIPT) process of BTMTP are remain existed, rather than as reported that the ESIPT had been canceled due to the stronger electron-withdrawing of sulfoxide group.