Pyrene bridged double[7]helicene embedded with a heptagonal ring†

To utilize [n]helicene-embedded polycyclic aromatic hydrocarbons in the development of circularly polarized materials high luminescence quantum yield and dissymmetric factors are essential to boost (chir)optical properties. Previously we have shown that the (chir)optical properties of pyrene fused mono helicenes can be significantly influenced by the fusing mode and molecular symmetry. We report in this manuscript the stereospecific synthesis and (chir)optical properties of C₁ symmetric pyrene fused double [7]helicene, where the helicene units are connected via hexagonal and heptagonal rings. In line with single helicene congeners, lower symmetric heptagon containing double helicene exhibited higher absorption and emission dissymmetric factors along with a significant increase in fluorescence quantum yield. Our findings in this manuscript provide further insights into the effect of molecular symmetry on the (chir)optical properties of single and double helicenes.