title: Modulation of excited-state intramolecular proton transfer by viscosity in protic media.
abstract: 3-Hydroxyquinolones undergo excited-state intramolecular proton transfer (ESIPT), resulting in a dual emission highly sensitive to H-bonding perturbations. Here, we report on the strong effect of viscosity on the dual emission of 2-(2-thienyl)-3-hydroxyquinolone in protic solvents. An increase in viscosity significantly decreases the formation of the ESIPT product, thus changing dramatically the ratio of the two emission bands. Time-resolved studies suggest the presence of solvated species characterized by decay times close to the solvent relaxation times in viscous media. The intramolecular H bond in this species is probably disrupted by the solvent, and therefore, its ESIPT requires a reorganization of the solvation shell for restoring this intramolecular H bond. Thus, the ESIPT reaction of this dye and its dual emission depend on solvent relaxation rates and, therefore, on viscosity. The present results suggest a new physical principle for the fluorescence ratiometric measurement of local viscosity.
authors.affiliation: Photophysique des Interactions Biomoléculaires, UMR 7175-LC1 du CNRS, Institut Gilbert Laustriat, Faculté de Pharmacie, Université Louis Pasteur, 67401 Illkirch, France. dmytro.yushchenko@pharma.u-strasbg.fr
authors.forename: Dmytro A
authors.initials: DA
authors.lastname: Yushchenko
authors.forename: Volodymyr V
authors.initials: VV
authors.lastname: Shvadchak
authors.forename: Andrey S
authors.initials: AS
authors.lastname: Klymchenko
authors.forename: Guy
authors.initials: G
authors.lastname: Duportail
authors.forename: Vasyl G
authors.initials: VG
authors.lastname: Pivovarenko
authors.forename: Yves
authors.initials: Y
authors.lastname: Mély
mesh_terms: D004579:Electron Transport; D005456:Fluorescent Dyes / Q000737:chemistry*; D006860:Hydrogen Bonding; D006912:Hydroxyquinolines / Q000737:chemistry*; D011522:Protons; D012997:Solvents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013997:Time Factors; D014783:Viscosity
chemical_list: D005456:Fluorescent Dyes; D006912:Hydroxyquinolines; D011522:Protons; D012997:Solvents