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Helical Threads: Enantiomerically Pure Carbo[6]Helicene Oligomers
Author(s) -
Schaack Cédric,
Sidler Eric,
Trapp Nils,
Diederich François
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201703024
Subject(s) - helicene , oligomer , enantiomer , monomer , chromophore , chemistry , fluorescence , yield (engineering) , oxidative coupling of methane , quantum yield , stereochemistry , crystallography , photochemistry , molecule , polymer chemistry , materials science , polymer , organic chemistry , physics , quantum mechanics , methane , metallurgy
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 %.