Abstract
The use of femtosecond laser pulses to selectively trigger an asymmetric photoreaction is demonstrated in this study. Depending on the handedness of the laser polarization, more R- or S-enantiomers of a racemate are gradually destroyed, leading to the generation of enantiomeric excess. The kinetic evolution of this excess is detected with a sensitive polarimeter. Hence, discrimination between racemic and achiral solutions and selective preparation of an enantiomeric excess within seconds is achievable. Furthermore, this technique opens the possibility for quantum control with chiral substances if the laser pulses which trigger the photoreaction are adjusted by pulse-shaping techniques.
Highlights
The concepts of symmetry and symmetry breaking play central roles in fundamental theories of physics, and symmetry properties are relevant for many applications across all disciplines of science and engineering
Chirality is an intrinsic structural property arising from symmetry considerations: a chiral object cannot be superimposed with its mirror image
One exploits the chiral properties of light interacting differently with a molecule and its mirror image, i.e., with enantiomers. These approaches rely on a difference in absorption of left versus right circularly polarized light (CD) or a change in the polarization direction of transmitted linearly polarized light (OA), respectively.[2]
Summary
The concepts of symmetry and symmetry breaking play central roles in fundamental theories of physics, and symmetry properties are relevant for many applications across all disciplines of science and engineering. Optically discriminating chiral from achiral objects is usually straightforward, as the spatial conformation can be deduced directly For microscopic objects, such as molecules, indirect spectroscopic methods are often employed using circular dichroism (CD) or optical activity (OA).[1] In both techniques, one exploits the chiral properties of light interacting differently with a molecule and its mirror image, i.e., with enantiomers. Exploiting the CD effect, one enantiomer absorbs light of one handedness stronger than the other and preferentially photodissociates if such a channel is available, causing an ee of the other enantiomer We transfer this idea to state-of-the-art fs laser spectroscopy allowing us (1) to generate and detect ee within seconds rather than days of illumination, (2) to follow the dynamical evolution of the asymmetric decomposition in quasi real-time, i.e., with a 100 Hz sampling rate, and (3) to enable future scenarios of chirality control with shaped fs laser pulses. Various schemes have been suggested using circularly[37,38] or combinations of linearly polarized laser fields[39,40,41,42,43,44,45] but no successful experiment has been reported yet in solution
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