title: Spectroscopic studies of enantiomeric discrimination in jet-cooled chiral complexes.
abstract: Van der Waals complexes formed between chiral molecules in the isolated gas phase were studied by combining supersonic expansion techniques with laser spectroscopy. The weakly bound diastereoisomers formed between a chiral secondary alcohol, butan-2-ol, and a chiral aromatic derivative such as 2-naphthyl-1-ethanol or 1-phenylethanol used as a resolving agent were discriminated on the basis of the spectral shifts of the UV S(0)-S(1) transition of the chromophore. Ground-state depletion spectroscopy (hole burning) has shown that, while only one structure was detected for the 1-phenylethanol/butan-2-ol homochiral complex, the heterochiral complex is trapped in the jet under two different conformations. Two isomers have also been shown for each diastereoisomeric pair of the 2-naphthyl-1-ethanol/butan-2-ol complexes. Using a semiempirical potential model, these isomeric forms were related to calculated structures which exhibit a folded or extended geometry depending on the solvent conformation (anti or gauche). The relative binding energy of the complexes involving R-1-phenylethanol and R- or S-butan-2-ol were obtained from fragmentation threshold measurements following two-color photoionization. Comparison of the diastereoisomers exhibiting a similar spectral signature shows that the homochiral pair is more stable than the heterochiral one by about 0.7 kcal/mol. The fragmentation threshold has been shown to depend on the jet-cooled isomer and this result addresses the role of conformational control in enantioselective interactions.
authors.affiliation: Laboratoire de Photophysique Moléculaire du CNRS, Université de Paris-Sud, Orsay, France.
authors.forename: K
authors.initials: K
authors.lastname: Le Barbu
authors.forename: A
authors.initials: A
authors.lastname: Zehnacker
authors.forename: F
authors.initials: F
authors.lastname: Lahmani
authors.forename: M
authors.initials: M
authors.lastname: Mons
authors.forename: F
authors.initials: F
authors.lastname: Piuzzi
authors.forename: I
authors.initials: I
authors.lastname: Dimicoli