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Given facile synthetic route and excellent photo stability, excited state intramolecular proton transfer (ESIPT)‐active luminous materials have gained more and more attention. Here, we focus on photo‐induced excitation process and the ESIPT reaction process for the novel 5‐benzothiazol‐2‐yl‐6‐hydroxy‐2‐methyl‐isoindole‐1,3‐dione (HPIBT) molecule. On the level of chemical geometries and infrared spectra, we verify that O─H⋯N of HPIBT should be enhanced. We find that a proton is likely to be attracted by enhanced electronic densities around N, that is, charge transfer impetus ESIPT trend. Combing potential energy curves and searching for transition state, we clarify the ultrafast ESIPT mechanism of HPIBT due to a low barrier, which legitimately explains previous experimental characteristics. [ABSTRACT FROM AUTHOR]

A novel acridone derivative, 10‐methyl‐indolo[2,3‐a]‐indolo[2,3‐a′]acridone (13), was reported by Fang and coworkers [J. Org. Chem. 2019, 84, 3832] in a previous paper. Spectroscopic studies on excited‐state intramolecular proton transfer (ESIPT) of 13 were mentioned, while the mechanism of ESIPT for 13 is deficiency. In this present work, based on the time dependent density functional theory (TDDFT), we investigated the ESIPT mechanism of 13 theoretically. The primary bond lengths, bond angles and the infrared (IR) vibrational spectra involved in the formation of hydrogen bonds verified that the intramolecular hydrogen bond should be strengthened, which manifests the tendency of excited state proton transfer. The redistribution of charge resulting from photoexcitation process reveals the driving force for ESIPT process. According to the results of theoretical potential energy curves along N‐H coordinate, an about 14.825 kcal/mol barrier has been found in the S0 state. However, a low barrier of 6.708 kcal/mol was calculated in the S1 state, which demonstrates that the proton transfer process is more likely to occur in the excited state. In other words, the proton transfer was facilitated by photoexcitation. Particularly, the study about ESIPT mechanism of 13 should be helpful for further understanding property of acridone derivatives. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

• Geometry parameters reveal strengthened intramolecular hydrogen bond of HDPB in S 1. • Photoinduced charge transfer facilitates the ESIPT reaction for HDPB system. • Low potential energy barrier reveals the ultrafast ESIPT process for HDPB molecule. In this work, the ESIPT mechanism of the novel HDPB compound is investigated. Probing into non-hydrogen bonding HDPB-O, we verify the stabilization of hydrogen bond. Based on simulating geometrical changes, we present O H⋯N of HDPB is enhanced by photoexcitation. Exploring MOs, we present charge recombination facilitates attracting proton, which promotes ESIPT tendency. Constructing potential energy curves (PECs) for HDPB, the low potential barrier 2.2107 kcal/mol is found for ESIPT process. Due to the low barrier, ultrafast ESIPT reaction occurs. It explains the non-fluorescent phenomenon of HDPB itself. This work clarifies ESIPT mechanism for HDPB, but also explains experimental phenomenon. [ABSTRACT FROM AUTHOR]