Investigation on the excited state intramolecular proton transfer process for the novel 2‐(3,5‐dichloro‐2‐hydroxy‐phenyl)‐benzooxazole‐5‐carboxylicacid system

Abstract

In view of the importance of excited state hydrogen bonding interactions and excited state proton transfer (ESPT) dynamical behaviors, in this work, we theoretically explore the excited state process for a novel 2‐(3,5‐dichloro‐2‐hydroxy‐phenyl)‐benzooxazole‐5‐carboxylicacid (DHPBC) system. On the basis of discrete Fourier transform (DFT) and time‐dependent density functional theory (TDDFT) methods, we reappear previous experimental reports with checking the reasonability of our theoretical level. We calculate and compare the primary geometrical parameters and hydrogen bonding energies around hydrogen bonding moieties, which reveals that the intramolecular hydrogen bond OH···N of DHPBC is enhanced in the S1 state. The increased electron densities around N atom contribute to attracting proton of hydroxyl upon the photoexcitation, which plays important roles in strengthening hydrogen bond and in facilitating excited state intra‐ or intermolecular proton transfer (ESIPT) process. Via constructing potential energy curves along with the ESIPT path, we verify that the ESIPT process of DHPBC system is ultrafast because of the low potential energy barrier. That should be the reason why the normal emission of DHPBC cannot be detected in previous experiment. This work not only clarifies the excited state hydrogen bonding interactions and fills the vacancy of specific ESIPT mechanism for DHPBC system in experiment, but also explains the fluorescence quenching phenomenon.

Existence of α‐mangostin conformers and effects of aprotic and protic solvents on their equilibria, UV–Vis spectra, and chemical descriptors: Density functional theory and time‐dependent density functional theory study

“…TD-DFT on optimized first-excited state geometry gives the fluorescence emission spectrum. Therefore, the TD-DFT method has been widely used to obtain the simulated UV-Vis spectra of interesting organic compounds such as tetrabenzocoronenes (TBC), [36] 2-(3,5-dichloro-2-hydroxy-phenyl)-benzooxazole-5-carboxylic acid (DHPBC), [37] 2,4-bis (benzooxazol-2 0 -yl) hydroquinone (2,4-DHBO) [38] and tetraphenyl ethene-2-(2 0 -hydroxyphenyl) benzothiazole (TPE-HBT). [39] Although α-mangostin exhibits a variety of pharmacological activities and has been used in traditional medicine, its properties, that is, physicochemical, thermodynamic, spectroscopic, and electronic structures have been hardly investigated.…”