Theoretical insights into effects of solvent polarity on excited‐state N–H proton transfer behavior for a new fluorophore of 3‐tosylamino‐N‐cyclohexylphthalimide

Compared with O–H···O‐type system, the N–H···O‐type system with excited‐state intramolecular proton transfer (ESIPT) provides a better research object for exploring kinetics and thermodynamics because the existence of amino group can be replaced by various groups. In this work, the ESIPT mechanism of a novel amino type proton donor (3TsAPI) has been studied, and its effects of solvent polarity have been investigated. We optimize the structures of 3TsAPI using density functional theory (DFT)/time‐dependent density functional theory (TDDFT) methods, and electronic spectra data are consistent with the experiment. Through the analyses of structural parameters and spectra related to hydrogen bonding, it is found hydrogen bonding is enhanced in S1 state, and analyses of bond critical point (BCP) parameters and core‐valence bifurcation (CVB) indexes show excited‐state hydrogen bonding is stronger in solvents with weaker polarity. We construct the potential energy curves and find polarity of solvents can regulate the potential energy barrier of ESIPT process and then further elucidate the ESIPT mechanism of 3TsAPI.