Dresden 2011 – scientific programme

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MO: Fachverband Molekülphysik

MO 9: Femtosecond Spectroscopy II

MO 9.2: Talk

Tuesday, March 15, 2011, 11:00–11:15, TOE 317

Transient UV/IR Spectroscopy of Hydrogen Bonded Photoacid Molecules — •Mirabelle Prémont-Schwarz¹, Dina Pines², Ehud Pines², and Erik T.J Nibbering¹ — ¹Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie Max Born str 2A 12489 Berlin — ²Department of Chemistry, Ben Gurion University of the Negev, P.O.B. 653, Beersheva 84125, Israel

Photoacids are organic molecules which experience a significant decrease in pKa upon electronic excitation, thereby making them much stronger acids in the excited state than in the ground state. This property has been greatly exploited in the last decades permitting dynamical proton transfer and hydrogen bonding research on femtosecond timescales. While their use is now quite well established, the photophysics leading to this drastic change in pKa remain unclear. In this study, transient UV pump/ IR probe spectroscopy is used in order to monitor the hydrogen stretching oscillator of 2-Naphthol, a prototype photoacid. The OH stretch provides insight into the nature of the electronic redistibution in the molecule as it is a very sensitive probe for hydrogen bonding and given that it is the local probe of the acidic bond. By looking at a series of solvents with different hydrogen bonding strengths as well as ternary systems, one is able to conclude about the importance of an already existing HB in the ground state as well as the relative contribution of dielectric vs specific interactions.