Can Brønsted Photobases Act as Lewis Photobases?

ABSTRACT

Dative bonding or Lewis acid-base chemistry underpins a large number of chemical phenomena in a variety of fields, such as catalysis, metal-ligand interactions, and surface chemistry. Developing light-controlled Lewis acid-base interactions could offer a new way of controlling and understanding such phenomena. Photoinduced proton transfer, that is, excited-state Brønsted acidity and basicity, has been extensively studied and applied. Here, in direct analogy to excited-state Brønsted basicity, we show that exciting a photobasic molecule with light generates a thermodynamic drive for the transfer of a Lewis acid from a donor to a photobasic molecule. We have used the archetypal BF3 as our Lewis acid and our photoactive Lewis bases are a family of quinolines, which are known Brønsted photobases as well. We have constructed the experimental Förster cycle for this system and have verified it computationally to demonstrate that a significant drive (0.2-0.7 eV) exists for the transfer of BF3 to a photoexcited quinoline. The magnitude of this drive is similar to those reported for Brønsted photobasicity in quinolines. Computational results from TDDFT and energy decomposition analysis show that the origin of such an effect is similar to the Brønsted photoactivity of these molecules, in that they follow the Hammett parameter of substituent groups. These results suggest that photobases may be capable of controlling the chemical phenomena beyond proton transfer and may open opportunities for a new handle in photocatalysis.