title: Excited-state intramolecular proton transfer (ESIPT) fine tuned by quinoline-pyrazole isomerism: pi-conjugation effect on ESIPT.
abstract: A series of quinoline/isoquinoline-pyrazole isomers (I-III), in which the pyrazole moiety is in a different substitution position, was strategically designed and synthesized, showing a system with five-membered intramolecular hydrogen bonding. Despite the similarity in molecular structure, however, only I undergoes excited-state intramolecular proton transfer, as evidenced by the distinct 560 nm proton-transfer emission and its associated relaxation dynamics. The experimental results support a recent theoretical approach regarding the conjugation effect on a proton (or hydrogen atom) transfer reaction (J. Phys. Chem. A 2009, 113, 4862-4867). The concept simply predicts that more extended pi conjugation, i.e., resonance, for proton-transfer tautomer species could allow for efficient delocalization of excess charge in the reaction center, resulting in a larger thermodynamic driving force for proton transfer.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Min-Wen
authors.initials: MW
authors.lastname: Chung
authors.forename: Tsung-Yi
authors.initials: TY
authors.lastname: Lin
authors.forename: Cheng-Chih
authors.initials: CC
authors.lastname: Hsieh
authors.forename: Kuo-Chun
authors.initials: KC
authors.lastname: Tang
authors.forename: Hungshin
authors.initials: H
authors.lastname: Fu
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
authors.forename: Shen-Han
authors.initials: SH
authors.lastname: Yang
authors.forename: Yun
authors.initials: Y
authors.lastname: Chi
mesh_terms: D003198:Computer Simulation; D003510:Cyclohexanes / Q000737:chemistry; D007536:Isomerism; D015394:Molecular Structure; D011522:Protons; D011720:Pyrazoles / Q000737:chemistry*; D011804:Quinolines / Q000737:chemistry*
chemical_list: D003510:Cyclohexanes; D011522:Protons; D011720:Pyrazoles; D011804:Quinolines; C031280:pyrazole; C506365:Cyclohexane; C037219:quinoline