부산대학교 도서관

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 %. [ABSTRACT FROM AUTHOR]