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

Abstract

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 p[z]-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.