Scorpion-Shaped Hybrid Double Helicenes via Orthogonal Alkyne Annulation Reactions.

Scorpion-shaped hybrid double helicenes, consisting of a [5] or [6] carbohelicene and an aza[4]helicene, have been successfully constructed by orthogonal alkyne annulations via an aryl C-I bond and amido N-H bond from polyaromatic ring-fused iodoisocoumarins. In spite of the unexpected instability upon aerobic oxidation upon ambient visible light irradiation over several days, both ultraviolet-visible absorption and photoluminescence spectra along with density functional theory calculations of these helicenes have been studied, which rely heavily on the bent polyaromatic ring-fused quinolizinone conjugate skeleton. In addition, the Stokes shifts of hybrid double helicenes are generally larger than those of the structurally similar mono-carbohelicenes.