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.