Heptannulated Perylene Diimides: Formation and Reactivity of Electron-Deficient Tropylium Cations and Heptafulvenes

The development of new π-conjugated motifs opens pathways to previously unexplored classes of organic semiconductors and functional dyes. In this study, five- and seven-membered carbocycles were fused at the ortho and bay regions of electron-deficient perylenes, starting from a common dialdehyde precursor. Structural analysis of the resulting perylene tetraesters, dianhydrides, and diimides (PDIs) revealed three distinct ring-fusion patterns and defined stereochemistry. The fused PDI cycloheptatrienes demonstrated susceptibility to acid-catalyzed transarylation, involving tropylium cation intermediates, which can be used preparatively. Under superacidic conditions, the PDI tropylium cations were directly observed and shown to undergo hydride-transfer reductions. Additionally, a fused PDI bis(heptafulvene) was synthesized by dehydrogenating a suitably substituted PDI cycloheptatriene. The final system contains two quinomethane units, which can be protonated to yield a stable tropylium-like dication.