Thursday July 10, 14h
ISMO Amphitheater
Conformation and complexation effects on one- and two-photon Photoelectron Circular Dichroism (PECD)
Chirality is ubiquitous in the biosphere, and molecular recognition such as drug-receptor interaction, is sensitive to chirality. Molecular flexibility also plays a key role in this process, allowing the ligand and the target to adapt their conformation to optimize the interaction. This work is a spectroscopic study of chiral molecules in the gas phase, under supersonic jet conditions, without the perturbations due to the solvent. It tackles the questions of chirality and conformation and rests on a chiroptical spectroscopy adapted to dilute media: PECD. PECD is defined as an intense asymmetry in the photoelectrons angular distribution, when a chiral molecule is ionized by circularly polarized light. Two experimental setups were used. The first one, on the DESIRS beamline of the SOLEIL synchrotron, rests on a one VUV photon ionization scheme. The second one, developed during this thesis, is a novel design allowing for conformer-selective PECD, using resonant two-photon ionization by narrow bandwidth lasers, which guaranties the conformer selectivity. Both setups have been applied to flexible molecules. For example, PECD signals opposite in sign have been observed for the conformers of 1-indanol. Induced chirality was observed in a weakly bound complex: PECD is observed after ionization of the orbitals localized on the achiral phenol, hydrogen-bonded to chiral methyloxirane. This is the first example of induced chirality in PECD. Finally, bioxirane’s complex electronic structure was studied thanks to the sensitivity of PECD to initial state properties.