Hyper-Rayleigh Scattering as a New Chiroptical Method: Uncovering the Nonlinear Optical Activity of Aromatic Oligoamide Foldamers
Résumé
Molecular helices based on self-organized aromatic oligoamide foldamers have been designed and prepared in their two enantiomeric forms in order to probe their second-order nonlinear chiroptical properties in solution. The quinoline oligoamides were rationally functionalized by electron-donating and electron-withdrawing groups to afford a gradual increase of the electronic polarization of the helical architectures. Their hyper-Rayleigh scattering (HRS) responses in solution were accordingly assessed, using either linearly polarized or circularly polarized incident light. Both methods allowed to observe nonlinear optical activity that was quantified, for the first time for molecular systems, through circular differential scattering intensity ratios. The hyper-Rayleigh optical activity (HROA) study reveals important charge transfer differences within the aromatic oligomers, depending on the helix handedness and on the extent of electronic polarization induced by the appended substituents. The origin of the enantiomeric difference is discussed considering both achiral and chiral contributions. Overall, we disclose the capabilities of HRS as a complementary chiroptical method, ideally suited for the analysis of chiral molecular and supramolecular systems in solution. Implementation of auxiliary polarization/detection techniques on our measurement setup is discussed to further increase the chiral discrimination sensitivity and extend the study to a wide rande of small molecular systems.
Domaines
Chimie
Origine : Fichiers produits par l'(les) auteur(s)