Helical Threads: Enantiomerically Pure Carbo[6]Helicene Oligomers

We report the synthesis of enantiomerically pure carbo[6]helicene oligomers with buta‐1,3‐diyne‐1,4‐diyl bridges between the helicene nuclei. The synthesis of monomeric (±)‐2,15‐bis[(triisopropylsilyl)ethynyl]carbo[6]helicene was achieved in 25 % yield over six steps. Pure (+)‐( P )‐ and (−)‐( M )‐enantiomers were obtained by HPLC on a chiral stationary phase. The dimeric (+)‐( P ) 2 ‐ and (−)‐( M ) 2 ‐configured and the tetrameric (+)‐( P ) 4 ‐ and (−)‐( M ) 4 ‐configured oligomers were obtained by sequential oxidative acetylenic coupling. The ECD spectra of the tetrameric oligomers displayed large Cotton effect intensities of Δ ϵ =−851  m −1  cm −1 at λ =370 nm (( M ) 4 ‐enantiomer). We transformed the buta‐1,3‐diyne‐1,4‐diyl bridge in the dimeric ( P ) 2 and ( M ) 2 oligomer by heteroaromatization into a thiene‐2,5‐diyl linker. Although the resulting chromophore showed reduced ECD intensities, it exhibited a remarkably strong fluorescence emission at 450–500 nm, with an absolute quantum yield of 25 %.