Hydrogen-Bond Dynamics and Solvation of Electronically Excited States as Determined by Femtosecond Vibrational Spectroscopy |
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Authors: | Erik TJ Nibbering Christian Chudoba Thomas Elsaesser |
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Affiliation: | Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Rudower Chaussee 6, D-12489 Berlin, Germany |
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Abstract: | The ultrafast dynamics of site-specific hydrogen bonds between an organic chromophore serving as hydrogen acceptor and a hydrogen-donating species in solution is studied by femtosecond vibrational spectroscopy. This new method gives specific insight into microscopic structural changes of hydrogen bonds initiated by electronic excitation of the chromophore. We study H-bonded complexes of coumarin 102 with the solvent CHCl3, and with phenol. Upon electronic excitation, the intermolecular hydrogen bond between proton donor and acceptor is cleaved within 200 fs, followed by a slower reorientation dynamics of the donor molecules extending into the picosecond regime. For CHCl3, this slower rearrangement is interpreted in terms of polar solvation. In complexes consisting of a coumarin molecule and two phenol moieties, the slower dynamics is related to geometry changes of the phenol–phenol hydrogen bond. The consequences of those results for a microscopic picture of polar solvation are discussed. |
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