title: Ultrafast dynamics of solute-solvent complexation observed at thermal equilibrium in real time.
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.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
authors.forename: Junrong
authors.initials: J
authors.lastname: Zheng
authors.forename: Kyungwon
authors.initials: K
authors.lastname: Kwak
authors.forename: John
authors.initials: J
authors.lastname: Asbury
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.forename: Ivan R
authors.initials: IR
authors.lastname: Piletic
authors.forename: M D
authors.initials: MD
authors.lastname: Fayer