CHIRAL DISCRIMINATION IN JET-COOLED VAN DER WAALS COMPLEXES: ELECTRONIC AND VIBRATIONAL SPECTROSCOPY

$^{a}$M. Mons, F. Piuzzi, I. Dimicoli, A. Zehnacker, F. Lahmani. Phys. Chem. Chem. Phys. 2 5065 (2000). $^{b}$K. Le Barbu, V. Brenner, Ph. Millie, F. Lahmani, A. Zehnacker-Rentien, J. Phys. Chem. A 102 128 (1998).Author Institution: Dept. of Chemistry, Laboratoire de Photophysique Moleculaire du CNRSChiral discrimination plays a key-role in life-chemistry and takes place through the formation of contact pairs implying short-range stereospecific interactions: spectroscopic measurements of jet-cooled van der Waals complexes of chiral molecules therefore provides a powerful strategy for addressing the question of chiral $recognition^{a}$. We present here a study of hydrogen-bonded complexes of chiral molecules by double resonance techniques, either UV/UV (hole burning $spectroscopy)^{b}$ or IR/UV fluorescence depletion spectra. Besides an spectroscopic means of discriminating between two enantiomers, the results presented here, coupled with DFT calculations, bring information on the nature of the forces responsible for chiral recognition. The role of the formation of a hydrogen-bonds network in chiral discrimination will be discussed

Photodissociation de NO

La fluorescence de NO* produit par photodissociation de NO2 a été étudiée en fonction de la longueur d’onde d’excitation dans le domaine 110-140 nm au moyen du rayonnement synchrotron de LURE ACO. Le spectre d’excitation de la fluorescence globale du fragment NO* reproduit le spectre d’absorption de NO2 dans cette région. Les spectres de fluorescence obtenus en excitant N02 dans la bande d’absorption située entre 131 et 125 nm ainsi qu’à 123,6 nm avec la raie de résonance du krypton sont diffus à cause de la superposition des émissions provenant de NO A2Σ+ et B2Π. Deux bandes de fluorescence distinctes ont pu être attribuées aux niveaux NO A (v’ = 2,1). Les mesures de durée de vie de NO Av’ = 1 confirment cette attribution. La population relative de ces deux niveaux est constante dans le domaine 120-130 nm. Un rapport de branchement constant NO A/B = 1 a également pu être évalué dans la même région

Localization of electronic and vibrational energy in the jet-cooled m-cyanophenol/o-cyanophenol dimer: laser induced fluorescence and fluorescence-dip IR spectra

International audienc

An Experimental and Theoretical Study of Jet-Cooled Complexes of Chiral Molecules: The Role of Dispersive Forces in Chiral Discrimination

International audienceIsomer formation in dimeric complexes of a chiral naphthalene derivative (2-naphthyl-1-ethanol) with nonchiral or chiral primary and secondary alcohols (n-propanol, 2-methyl-1-butanol, 2-butanol, 2-pentanol) has been studied by hole-burning spectroscopy. Besides the spectroscopic discrimination between the homochiral and heterochiral complexes, previously observed in the fluorescence excitation spectra, ground-state depletion experiments have shown that each diastereoisomer is cooled in the jet in several isomeric forms. To get information on the structures of the complexes and on the influence of the solvent conformations of these structures, semiempirical calculations that rely on the exchange perturbation method have been performed. It has been shown that the most stable complexes involve a H-bond between the chromophore acting as the donor and the solvent and that they involve anti and gauche conformations of the solvent. The binding energy of the complexes results from a subtle balance between electrostatic and dispersive forces: the complexes involving the gauche and anti conformers of the solvent differ from each other by the amount of dispersion energy relative to the total interaction energy. The increase in the dispersive forces calculated for the complexes with the anti conformers has been related to a larger red shift of the absorption spectrum and is suggested to play a role in the observed chiral discrimination

IR-UV investigation of the structure of the 1-phenylethanol chromophore and its hydrated complexes

International audienc