Photosensitizing Au(I) Catalysis With Coumarins.

Gold catalysis shows versatility in a wide range of challenging transformations, wherein light-driven reactions open new pathways. Understanding the factors that impact photosensitization is essential for harnessing the reactivity of excited states in gold photoredox and energy transfer catalysis. We use a Au(I) complex attached to a 3-amino coumarin chromophore (1) to investigate the impact of intramolecular photosensitization on its photophysical and photochemical properties. The potential of 1 to mediate light-driven electron- or energy-transfer processes was tested in two representative cross-coupling reactions. 1 performs moderately in these reactions, which we attribute to the emergence of competing pathways, as indicated by photophysical studies. At 298 K 1 emits weakly, which is attributed to the coumarin chromophore based on UV-vis absorption and emission spectroscopy, and supported by DFT calculations. Although advantageous in coupling the coumarin to the gold complex, self-quenching by the amide group results in a reduction of the emission from 1 relative to that of 3-amino coumarin. At 77 K 1 shows phosphorescence, which is absent in the coumarin alone, indicating intramolecular energy transfer is possible. These data indicate that photochemical activation of gold catalysis holds potential, but effective energy transfer between chromophore and catalyst remains a challenge.