Hydrogen bonding interactions induced excited state proton transfer and fluoride anion sensing mechanism for 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐5‐carboxylicacid

Abstract

AbstractThe present work explores and reports photo‐induced behavior and excited state intramolecular proton transfer (ESIPT) process for the novel 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐5‐carboxylicacid (DICH) compound. Our theoretical investigation implies that two intramolecular hydrogen bonds (O1─H2···N3 or O4─H5···O6) of DICH form are strengthening in the first excited state by comparing bond lengths, bond angles, and infrared (IR) spectra, which may facilitate the ESIPT process effectively. Particularly, the changes of O1─H2···N3 are bigger than O4─H5···O6, which demonstrates that the ESIPT is more likely to happen along with O1─H2···N3. Within the framework of MOs analysis, intramolecular charge transfer phenomenon can be found, which could be a reasonable evidence for confirming the occurrence of the ESPT process in the S1 state. We theoretically construct the potential energy curves for DICH system based on fixing both O1─H2 and O4─H5 bond lengths and optimizing structures in both S0 and S1 states. Through the comparisons of potential barriers among stable configurations, we confirm the S1‐state DICH‐PT1 (proton‐transfer tautomer along with O1─H2···N3) should be the most reasonable configuration ascribed to previous experimental emission peak. Furthermore, we also predict and explain the fluoride‐sensing mechanism for DICH system that the deprotonation reaction bringing from fluoride anion inhibits the initial ESIPT process of DICH, which results in the novel changes of ultraviolet‐visible (UV‐Vis) spectra that plays the roles in fluorescence response. We sincerely hope this work could provide essential insights into the design and function of ESIPT as well as florescence sensor for optoelectronic applications.