Modular Synthesis of Polycyclic Aromatic Hydrocarbons Enabled by Electrophotocatalysis

We report a modular electrophotocatalytic platform for the construction of polycyclic aromatic hydrocarbons (PAHs) via radical annulations. Using structurally engineered peri-xanthenoxanthene-derived catalysts bearing phosphonium and sulfone groups, we can access highly reducing excited states (down to –3.05 V and –3.44 V vs SCE) by combining electrochemical priming with green-light irradiation. This dual activation enables C(sp²)–C(sp²) and C(sp)–C(sp²) bond formation from otherwise inert aryl halides and alkynes under mild, metal-free conditions. Spectroelectrochemical studies, characterized by theoretical calculations, reveal that the doubly reduced photoexcited species are the key reactive intermediates. The method tolerates diverse functional groups and topologies, affording mono-, bi-, and tri-annulated products as well as cascade and alkyne-driven cycloaromatizations. This work introduces a powerful synthetic blueprint for π-conjugated frameworks, expanding the scope of radical chemistry in PAH synthesis beyond conventional oxidative protocols.