Photonenergy-Controlled Symmetry Breaking with Circularly Polarized Light


  • We are grateful to the general technical staff of the ASTRID synchrotron at ISA and the SOLEIL facilities as well as to N. C. Jones, J.-F. Gil, G. Garcia, and N. de Oliveira for technical and beamline assistance. We thank J.-P. Laugier for recording scanning electron micrographs. This work was supported by a French National Centre of Space Research Fellowship (CNES) to C.M., the International Max Planck Research School at MPS for a PhD scholarship to C.G., and the Agence Nationale de la Recherche (ANR-07-BLAN-0293 and ANR-12-IS07-0006). This work was furthermore supported by the I3 Integrated Activity on Synchrotron and Free Electron Laser Science (IA-SFS), contract no. RII3-CT-2004-506008, under the Research Infrastructure Action of the FP6 EC program Structuring the European Research Area as well as the European Community’s Seventh Framework Program (FP7/2007-2013; grant no. 226716).


Circularly polarized light (CPL) is known to be a true chiral entity capable of generating absolute molecular asymmetry. However, the degree of inducible optical activity depends on the λ of the incident CPL. Exposure of amorphous films of rac-alanine to tunable CPL led to enantiomeric excesses (ee) which not only follow the helicity but also the energy of driving electromagnetic radiation. Postirradiation analyses using enantioselective multidimensional GC revealed energy-controlled ee values of up to 4.2 %, which correlate with theoretical predictions based on newly recorded anisotropy spectra g(λ). The tunability of asymmetric photochemical induction implies that both magnitude and sign can be fully controlled by CPL. Such stereocontrol provides novel insights into the wavelength and polarization dependence of asymmetric photochemical reactions and are highly relevant for absolute asymmetric molecular synthesis and for understanding the origins of homochirality in living matter.