Theoretical investigation into the deciphering effects of atomic electronegativity on 2-hydroxy-phenyl-tafamidis: A time-dependent density functional theory study

In light of the potential probe applications of 2-hydroxy-phenyl-tafamidis (2HPT) and its derivatives with different atomic electronegativity (2HPT-O, 2HPT-S, and 2HPT-Se), the mechanisms of excited state intramolecular proton transfer (ESIPT) of 2HPT derivatives have been investigated in this work. Via probing into the geometric parameters of hydrogen bond O-H center dot center dot center dot N, infrared vibrational spectroscopy, and bond critical point values, we can confirm that hydrogen bonding is enhanced in the first excited state (S-1). It is worth mentioning that the enhancement of hydrogen bonding in the S-1 state by low atomic electronegativity 2HPT-Se is particularly important. In light-induced excitation, by comparing the changed behaviors of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals, it could be found that photo-induced charge transfer happens in excited molecules, and charge redistribution facilitates ESIPT reaction. Particularly, the low atomic electronegativity could promote the ESIPT process for 2HPT system. In order to clarify the detailed ESIPT mechanism, we construct the potential energy curves, search for the transition state form, and determine the ESIPT mechanism for 2HPT fluorophores. In this work, we not only elucidated the excited state behavior of 2HPT systems but also proposed a novel mechanism for regulating ESIPT by atomic electronegativity.