Molecular crystal architecture and optical properties of a thiohelicenes series containing 5, 7, 9, and 11 rings prepared via photochemical synthesis

Helicenes are intrinsically chiral helical molecules structurally characterized by orthofusion of aromatic rings. A series of racemic heterohelicenes composed of thiophene and benzene rings alternated in the helical chain were prepared via photochemical irradiation. The availability of large systems containing 9 and 11 condensed rings allows a better understanding of both optical properties and solid-state organization of thiohelicene molecules. The conformation and the crystal architecture of thiohelicenes, containing up to 11 rings show ring distortions smaller than in carbohelicenes. All the crystals obtained are racemates, and heterochiral assembling is dominant also for the larger systems.