title: Combined Experimental and Theoretical Study of the Transient IR Spectroscopy of 7-Hydroxyquinoline in the First Electronically Excited Singlet State.
abstract: The photophysics of 7-hydroxyquinoline (7HQ) in protic media results from an interplay of acid-base chemistry, prompted by the effects of photoacidity of the hydroxyl group and photobasicity of the nitrogen atom in the quinoline aromatic system. With ultrafast IR spectroscopic measurements, we follow the proton transfer dynamics of 7HQ in its four possible charged forms in methanol solution. Using deuterated methanol as solvent, we determine deuteron transfer rates from the neutral to the zwitterionic form to be 330 ps, those from the cationic form to the zwitterionic form to be 170 ps, and those from the anionic form to the zwitterionic form to be 600 ps. We compare the observed IR-active fingerprint marker patterns in the electronic ground state and the first electronically excited1Lb-state with those calculated using density functional theory and time-dependent density functional theory, respectively, and find good correspondence between experimental and calculated transitions. The calculations provide insight into the nature of electronic excitation of these four different charged forms of 7HQ, suggesting the key role of electronic charge distribution changes upon electronic excitation of 7HQ and hydrogen bond changes at the donor hydroxyl and acceptor nitrogen moieties.
authors.affiliation: Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg , Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Hoffmann
authors.affiliation: Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie , Max Born Strasse 2A, 12489 Berlin, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Ekimova
authors.affiliation: Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg , Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany.|Physics Department, Freie Universität Berlin , Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Gül
authors.initials: G
authors.lastname: Bekçioğlu-Neff
authors.affiliation: Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie , Max Born Strasse 2A, 12489 Berlin, Germany.
authors.forename: Erik T J
authors.initials: ET
authors.lastname: Nibbering
authors.affiliation: Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg , Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Sebastiani