Self-induced charge transfer activation enables metal-free C–H coupling of polycyclic aromatic hydrocarbons under photo irradiation

Abstract

Axially chiral three-dimensional nanographenes (3D NGs) represent promising scaffolds for chiral optoelectronic materials, yet their direct synthesis remains challenging because of the oxidative fragility of π-extended arenes. Here we report a metal-free, photo-irradiated oxidative C–H/C–H biaryl coupling of polycyclic aromatic hydrocarbons mediated by a Brønsted acid and O₂. The reaction efficiently converts π-extended arenols, including fluoranthene derivatives, into structurally diverse axially chiral 3D NGs without overoxidation. Mechanistic studies reveal that self-induced charge transfer (CT) complexation between protonated and neutral arenols triggers photoinduced formation of radical cations, as supported by UV-vis, ESR and DFT analyses. The obtained axially chiral 3D NGs exhibit high configurational stability and photophysical features rationalized by TD-DFT calculations. This strategy establishes a general platform for constructing axially chiral 3D NGs from π-extended arenols under metal-free conditions.