Synthesis of Alternatively-Twisted Nanographenes by Semi-Deprotection-Induced Cyclization

Twisted nanographenes (NGs) are currently attracting a lot of attention owing to their geometrical and electronic structures that differ substantively from conventional planar and nonplanar NGs, while the strategic synthesis of twisted NGs is still a topic of interest because the products are often interconvertible among unidirectionally, alternatively, or randomly twisted geometries and otherwise obtained as a mixture of them. Herein, we report the conformationally specific synthesis of twisted NGs where the geometry was reinforced by introducing 1,4-dioxane rings at a K-region of a central pyrene core that bears a large contortion. The 1,4-dioxane rings were generated by semi-deprotection, of tetraoxa[4.4.4]­propellanes in precursor molecules, which were confirmed to be engaged in forming C–C bonds via a Friedel–Crafts type mechanism. The large contortion within the pyrene core causes a narrowed HOMO–LUMO gap on account of unusual pz-lobe overlap between +z and −z sides, giving rise to red emission with a high quantum yield of 94% as well as stable redox processes of 2e– uptake/release.