Photochemistry with Plane-Polarized Light: Controlling Photochemical Reactivity via Spatially Selective Excitation

Photochemical reactions are intrinsically difficult to control because they involve high-energy excited state species. Herein, we report a novel approach towards controlling photochemical reactions via using spatially selective excitation of specific electronic transitions. This can be performed using photochemical irradiation with plane-polarized light of a photoreactive compound uniformly aligned in a nematic liquid crystalline (LC) medium. Having chosen cyclopropenone photodecarbonylation as a proof-of-concept reaction, we demonstrated that it could be controlled via changing an angle between the incident light polarization plane and the LC director. We showed that two specific partially forbidden electronic transitions were mostly responsible for this photochemical reaction. We envision that this simple general method can be useful in experimental studies of fundamental details of various photochemical processes, as well as can help to increase selectivity of photochemical transformations.