A saddle-shaped OBO-doped nanographene: facile synthesis, adaptive double-layer assembly, and enhanced Lewis acidity

Current OBO-doped nanographenes (NGs) are predominantly planar, and the precise synthesis of curved OBO-doped NGs remains a challenge owing to their limited thermodynamic stability. Herein, we report a two-step synthesis of the first saddle-shaped OBO-doped NGs (1a-1c) built upon a corannulene core. Pristine 1a exhibits reversible thermo-responsive behavior characteristic of a lower critical solution temperature (LCST)-type response. Single-crystal X-ray diffraction analysis combined with theoretical calculations reveals that these nanographenes adopt a saddle geometry. Notably, the incorporation of bulky triisopropylphenyl (TIPP) groups not only improves thermodynamic stability but also enables 1c to form ordered, adaptive bilayer assemblies in the solid state, inducing dramatic flattening of the corannulene core-a rare example of structure adaptation driven by supramolecular assembly rather than intramolecular steric effects. Crystallographic analyses further demonstrate that such geometric distortion increases the accessibility of boron centers. Consequently, the saddle-shaped topology imparts significantly enhanced Lewis acidity to these NGs, facilitating the first crystallographically characterized dual methanol coordination on the concave surface of a boron-doped nanographene. This work introduces a unique topological scaffold combining non-planarity, multi-heteroatom doping, and bilayer assembly, expanding the family of heteroatom-doped NGs with novel topologies.