Identifying the Role of Excited-State Proton Transfer and Photoinduced Electron Transfer in Detecting Hypochlorous Acid for a Benzothiazole-Based Colorimetric Fluorescent Probe

Abstract In this work, the fluorescence mechanism of Hypochlorous Acid (HOCl) chemosensor JBD with 2-(20-Hydroxyphenyl) benzothiazole (HBT) as fluorophore has been investigated by density functional theory (DFT) and time-dependent DFT methods. For JBD probe, the potential energy barrier for the forward excited-state (S 1 ) intramolecular proton transfer (ESIPT) is 0.71kcal/mol, while for reversed ESIPT is 8.47kcal/mol. The stability of Keto isomers provides reliable evidence for the existence of two isomers of JBD in S 1 state. Dual fluorescence of JBD has been observed in the experiment, which is a typical feature for the ESIPT. Through the analysis of the change of intramolecular charge transfer (ICT) extent, it is found that JBD undergo a significant geometric rearrangement upon photoexcitation, which leads to the large Stokes shift. After adding HOCl, the double emission is closed and the fluorescence disappears. We use hole-electrons to analyze the charge distribution, providing evidence for possibility of ICT processes occurring.