Twist and Shine: Ultra‐Narrow Red Emission from Nitrogen and Oxygen Co‐Doped Hetero‐Nanographenes

Nanographenes, known for their exceptional optoelectronic properties, have garnered significant interest for their tunable electronic structures, particularly through heteroatom doping. Herein, we report the synthesis of two twisted hetero-nanographenes (h-NGs) co-doped with nitrogen and oxygen via a three-step strategy, where the tandem Pictet-Spengler cyclization and ipso-aromatic substitution serve as a key step. Both h-NGs incorporate a unique bis-fused diazacoronene (BFDAC) core, with one further extending the π-system via peri-fusion of four benzopyran units. Single-crystal analyses reveal that BFDAC core of both h-NGs adopts a highly twisted geometry, whereas the benzopyran-fused one has enhanced rigidity. Theoretical studies confirm a global aromaticity with 30 π-electrons delocalized along BFDAC periphery. Notably, co-doping enables precise electronic tuning, with pyridinic nitrogen lowering the LUMO level and benzopyran oxygen raising the HOMO level. Both h-NGs display the red photoluminescence (PL), and the benzopyran-fused derivative exhibits an ultra-narrow emission with a full-width at half-maximum of 19 nm, among the narrowest reported for organic red-emitting materials. Both h-NGs exhibit acid-responsive optical behavior including near-infrared absorption shift and PL quenching, providing additional functional versatility.