Scorpion-Shaped\nHybrid Double Helicenes via Orthogonal\nAlkyne Annulation Reactions

Scorpion-shaped\nhybrid double helicenes, consisting of\na [5] or\n[6] carbohelicene and an aza[4]helicene, have been successfully constructed\nby orthogonal alkyne annulations via an aryl C–I bond and amido\nN–H bond from polyaromatic ring-fused iodoisocoumarins. In\nspite of the unexpected instability upon aerobic oxidation upon ambient\nvisible light irradiation over several days, both ultraviolet–visible\nabsorption and photoluminescence spectra along with density functional\ntheory calculations of these helicenes have been studied, which rely\nheavily on the bent polyaromatic ring-fused quinolizinone conjugate\nskeleton. In addition, the Stokes shifts of hybrid double helicenes\nare generally larger than those of the structurally similar mono-carbohelicenes.