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  • Title: Ultrafast dynamics of solute-solvent complexation observed at thermal equilibrium in real time.
    Author: Zheng J, Kwak K, Asbury J, Chen X, Piletic IR, Fayer MD.
    Journal: Science; 2005 Aug 26; 309(5739):1338-43. PubMed ID: 16081697.
    Abstract:
    In general, the formation and dissociation of solute-solvent complexes have been too rapid to measure without disturbing the thermal equilibrium. We were able to do so with the use of two-dimensional infrared vibrational echo spectroscopy, an ultrafast vibrational analog of two-dimensional nuclear magnetic resonance spectroscopy. The equilibrium dynamics of phenol complexation to benzene in a benzene-carbon tetrachloride solvent mixture were measured in real time by the appearance of off-diagonal peaks in the two-dimensional vibrational echo spectrum of the phenol hydroxyl stretch. The dissociation time constant tau(d) for the phenol-benzene complex was 8 picoseconds. Adding two electron-donating methyl groups to the benzene nearly tripled the value of tau(d) and stabilized the complex, whereas bromobenzene, with an electron-withdrawing bromo group, formed a slightly weaker complex with a slightly lower tau(d). The spectroscopic method holds promise for studying a wide variety of other fast chemical exchange processes.
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