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, visible light-induced 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.