Monolayer and Bilayer Nitrogen-Doped Nanographenes Constructed by Cascade Cyclization

Nitrogen-doped nanographenes (NGs) with precise structures are attractive because of their tunable electronic structures and supramolecular assembly behaviors. However, the synthesis of structurally diverse architectures, especially discrete bilayer systems, remains challenging. Herein, we report a cascade photo-induced radical cyclization (PIRC) strategy for the programmable synthesis of a series of peripheral nitrogen-doped NGs with tunable monolayer and bilayer architectures. Starting from nitrogen-doped nanographene 1 as a versatile structural platform, π-extension affords the larger monolayer nanographene 2, whereas modulation of the peripheral steric substituents enables the formation of a discrete bilayer assembly, (3)₂. Single-crystal x-ray diffraction confirmed the monolayer structures of 1 and 2, while NMR spectroscopy, MALDI-TOF mass spectrometry, and DFT calculations revealed that (3)₂ adopts a bilayer configuration. Compared with the monolayer analogues, the bilayer assembly shows broadened and blue-shifted absorption features characteristic of H-type coupling. More importantly, peripheral N─H functionalities enable solvent-responsive dissociation of the bilayer through hydrogen bonding with oxygen-containing solvents, leading to a solvent-switchable transformation between bilayer and monolayer states. The aggregation behavior of (3)₂ is governed by the orthogonality between π-π interactions and hydrogen bonding, giving rise to a unique solvent-dependent yet concentration-independent structural transformation.