Cyclobishelicenes: shape-persistent figure-eight aromatic molecules with promising chiroptical properties

Abstract : Cyclobis[n]helicenes (n = 3 or 5) are chiral D2-symmetric p-conjugated macrocycles with stable lemniscular, or figure-eight, shapes. The conformational analysis of five different cyclobis[n]helicenes revealed that these molecules can only exist as their lemniscular conformers with high barriers to enantiomerization (>200 kJ.mol-1). The enantiomers of a cyclobis[5]helicene were resolved by HPLC and their unusual chiroptical properties were attributed to the inherent chirality of their macrocyclic figure-eight.