Speaker
Description
Circularly polarized light (CPL) induces different populations in left- and righ-handed versions of randomly oriented chiral molecules. Such differences lead to differences in the product yields of photochemical reactions. Thus, CPL triggers all-optical enantioselective photochemistry. But the difference is usually below 0.1%, rendering CPL impractical for photochemical applications. Therefore, photochemistry still invariably relies on chemical (instead of all-optical) methods to control enantioselectivity. A practical all-optical alternative would allow unprecedented temporal and spatial control over the enantioselectivity of photochemical reactions. Beyond applications like enantiomeric enrichment, such control would also enable new technologies, like enantiomeric switches [2], which are currently hindered by CPL’s low selectivity.
Here we introduce two schemes (see Fig. 1) to enantioselectively control the excited state population of electronic states in chiral molecules. Our proposal [3] can be realized using readily available fs technology [4], requires neither all-resonant transitions nor long electronic coherence times, and yields enantioselectivities close to 30%. Our findings are supported by analytical theory revealing the role of light’s polarization in both schemes, and by ab-initio simulations.
In the 1- vs 2-photon scheme, we find that the enantioselectivity oscillates on the scale of the fundamental wavelength. Thus, maintining enantioselectivity requires contraining the interaction region accordingly, e.g. using appropriately oriented thin flat liquid microjets. We find that the oscillation of the enantioselectivity across the interaction region can be avoided by using the 2- vs 3-photon scheme in Fig. 1b. Including liquid water dispersion yields oscillations on the scale of 50 μm, which can be easily addressed.
Fig. 1:
[2] B L Feringa, Angew. Chem. Int. Ed. 56, 11060 (2017)
[3] A Ordóñez et al., arXiv 2309.02392 (2023)
[4] C Burger et al., Opt. Express 25, 31130 (2017)
