Theoretical insights into photochemical behavior and ESIPT mechanism for 2,6-dimethyl phenyl derivatives

Highlights: • AIM and MEP analyses reveal the stabilization of hydrogen bonding interactions. • Enhanced hydrogen bond and charge redistribution reveal ESIPT tendency. • HBT-Py and HBT-Py-DMP undergoes ultrafast ESIPT reactions. • Nonpolar solvents contribute to ESIPT behavior for HBT-Py and HBT-Py-DMP. Belonging to derivatives of 2-(2-hydroxyphenyl)benzothiazole, two novel excited state intramolecular proton transfer (ESIPT)-active 2,6-dimethylphenyls derivative dyes (HBT-Py and HBT-Py-DMP) are investigated theoretically. We mainly focus on the excited state photochemical behaviors and ESIPT mechanisms for these two compounds. Photo-induced intramolecular hydrogen bond has been confirmed to be enhanced, which is the first premise for excited state dynamics. Charge reorganizations and electronical densities changes resulting from photoexcitation reveal ESIPT tendency. We further perform potential energy curves (PECs) simulations, which verifies the ultrafast ESIPT mechanism for these two compounds. Particularly, we present that nonpolar solvents could accelerate ESIPT behaviors.