Theoretical insights into the directionality of ESIPT behavior of BTHMB molecule with two proton acceptors in solution

We theoretically explore the spectral properties and excited-state intramolecular proton transfer (ESIPT) process for 3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methoxy-benzaldehyde (BTHMB). After analyzing structural parameters, infrared (IR) spectra, electron density and reduced density gradient, the strengthened intramolecular H-bond in the first excited-state is proved. According to potential energy curves, we confirm that the two isomers of BTHMB can be transformed into each other in the S0 state. After photoexcitation, both isomers can take place ESIPT process. Due to similar and low barriers of two proton transfer pathways, the two ESIPT directions from OH group toward O and N atom in BTHMB can be feasible.

Automated summary

In this study, the spectral properties and excited-state intramolecular proton transfer process of BTHMB were theoretically explored, revealing that both isomers can undergo ESIPT after photoexcitation in feasible directions towards oxygen and nitrogen atoms.