Harnessing Excited-State Intramolecular Proton-Transfer Reaction via a Series of Amino-Type Hydrogen-Bonding Molecules

• Published in: The journal of physical chemistry letters Vol. 6; no. 8; pp. 1477 - 1486
• Main Authors: Tseng, Huan-Wei, Liu, Jun-Qi, Chen, Yi-An, Chao, Chi-Min, Liu, Kuan-Miao, Chen, Chi-Lin, Lin, Tzu-Chieh, Hung, Cheng-Hsien, Chou, Yen-Lin, Lin, Ta-Chun, Wang, Tian-Lin, Chou, Pi-Tai
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16.04.2015
• Subjects: Amines - chemistry; Electrons; Hydrogen Bonding; Protons; proton transfer; dual emission; hydrogen bond
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.5b00423

A series of new amino (NH)-type hydrogen-bonding (H-bonding) compounds comprising 2-(2′-aminophenyl)­benzothiazole and its extensive derivatives were designed and synthesized. Unlike in the hydroxyl (OH)-type H-bonding systems, one of the amino hydrogens can be replaced with electron-donating/withdrawing groups. This, together with a versatile capability for modifying the parent moiety, makes feasible the comprehensive spectroscopy and dynamics studies of amino-type excited-state intramolecular proton transfer (ESIPT), which was previously inaccessible in the hydroxyl-type ESIPT systems. Empirical correlations were observed among the hydrogen-bonding strength (the N–H bond distances and proton acidity), ESIPT kinetics, and thermodynamics, demonstrating a trend that the stronger N–H···N hydrogen bond leads to a faster ESIPT, as experimentally observed, and a more exergonic reaction thermodynamics. Accordingly, ESIPT reaction can be harnessed for the first time from a highly endergonic type (i.e., prohibition) toward equilibrium with a measurable ESIPT rate and then to the highly exergonic, ultrafast ESIPT reaction within the same series of amino-type intramolecular H-bond system.