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 2‐(20‐hydroxyphenyl) benzothiazole‐4‐(1‐isocyanovinyl)pyridine (JBD) has been investigated by density functional theory (DFT) and time‐dependent DFT (TDDFT) methods. For JBD probe, the potential energy barrier for the forward excited‐state (S 1 ) intramolecular proton transfer (ESIPT) is 0.71 kcal/mol, while for reversed ESIPT is 8.47 kcal/mol. Due to the keto isomers are stable, the two isomers can be existed in the S 1 state. Dual fluorescence of JBD has been observed in the experiment, which is a typical feature for the ESIPT. By analyzing the change of the degree of intramolecular charge transfer (ICT), JBD could undergo a significant geometric rearrangement upon photoexcitation, leading to the large stokes shift. Adding HOCl, the double emission is turned off and the fluorescence disappears. In order to provide the possibility of ICT processes, the charge distribution has been analyzed by hole‐electrons.