Pyrene-4,5-dione as a Visible-Light Organic Photocatalyst for Photooxidation, Photoredox, Energy Transfer, and...

Pyrene-4,5-dione (PQ) is demonstrated to be a metal-free, visible-light organic photocatalyst capable of mediating four major photochemical activation modes: photooxidation, energy transfer, photoredox, and hydrogen atom transfer (HAT). Under mild conditions using blue LEDs, PQ enables diverse synthetic transformations, including singlet oxygen oxidations, [2 + 2] cycloadditions, C-H fluorination, reductive C-C bond formation, oxidative hydroxylation of boronic acids, and HAT-driven alkylation. Its performance is comparable to benchmark systems, while offering the advantages of visible-light absorption and a greener profile compared to typical metal-complex photocatalysts. PQ can be recovered chromatographically (typically 85-90% mass recovery) with no evidence of structural change or degradation. Further, as a proof-of-concept, the reductive C-C coupling was performed in continuous flow, delivering up to 85% yield at 0.17 mmol h^-1 in a 4 mL reactor and 83% yield at 0.41 mmol h^-1 upon numbering-up to a 10 mL reactor. This work highlights the potential of PQ as a practical and versatile photocatalyst for visible-light-driven organic synthesis.