Investigating Methyl Substitution Position Effect on the ESIPT Process in 2-(2'-Hydroxyphenyl) Benzothiazole Derivatives

Yilong Wang; You Li; Dongxiang Li

doi:10.6911/WSRJ.202506_11(6).0010

Authors

Yilong Wang
You Li
Dongxiang Li

DOI:

https://doi.org/10.6911/WSRJ.202506_11(6).0010

Keywords:

Hydrogen bond, DFT/TDDFT, HBT derivatives, ESIPT.

Abstract

Substituent position significantly influences the excited-state intramolecular proton transfer (ESIPT) behavior of 2-(2-hydroxyphenyl)-benzothiazole (HBT) derivatives, which are widely applied in fluorescent sensing. This study compares o-HBT-H and m-HBT-H to explore methyl substitution effects on ESIPT. Using by density-functional theory (DFT) and time-dependent DFT methods, optimized geometries calculations reveal that m-HBT-H exhibits stronger intramolecular hydrogen bonding in S₁ state, enhancing ESIPT activity. Electrostatic potential and frontier molecular orbitals FMOs analyses confirm methyl substitution modulates charge redistribution, strengthening intramolecular interactions. Infrared (IR) spectra and potential energy curves further validate the better ESIPT performance for m-HBT-H. These results provide a theoretical basis for designing advanced HBT-based fluorescent probes with tailored ESIPT properties.

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