Tuning fluorescence behavior and ESIPT reaction of 2-(2-Hydroxy-phenyl)-4(3H)-quinazolinone by introducing different groups

Abstract

Although the excited state intramolecular proton transfer (ESIPT) process and photophysical properties of 2-(2-Hydroxy-phenyl)-4(3H)-quinazolinone (HPQ) have been extensively explored, a comprehensive study of the substitution effects on HPQ is still lacking in theory. Given this situation, HPQ molecules with different electronic substituents are systematically investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT) methods in this work. Two different substituents, including –NH2 (electron-donating group) and –CN (electron-withdrawing group), are selected to complete this study. The fluorescence quenching phenomenon of HPQ in the keto form is well explicated by the twisted intramolecular charge transfer (TICT). Besides, the substitutions of –NH2 and –CN on HPQ give rise to the larger Stokes shifts and reproduces the dual fluorescence property. The primary parameters related to the intramolecular hydrogen bonds (IHBs) and the infrared (IR) vibration spectra of the O1–H2 reveal that all the IHBs for HPQ and its derivatives are enhanced in the S1 state. Meanwhile, from the calculated potential energy curves, it can be inferred that the introduction of –NH2 and –CN enlarges the excited-state energy barrier of the proton transfer process for HPQ. Therefore, we have reason to conclude that the substitutions of –NH2 and –CN groups on HPQ significantly affect the ESIPT process and triggers distinct photophysical behaviors.