Perylene Diimide-Embedded Double [8]Helicenes.

The rational design and modification of the helix is of significance for fully promoting properties of configurationally stable materials for various applications in chiral science. Herein, a straightforward, sterically less demanding synthetic approach involving hybridization between two [6]helicene subunits and a perylene diimide (PDI) scaffold are presented, affording perylene diimide-embedded double [8]helicenes (PD8Hs) which represent the highest double carbohelicenes reported thus far. Due to the structural features of PDI and [6]helicene, the PD8Hs have six stereoisomers including two pairs of enantiomers and two mesomers. Such structural diversity is unprecedented in the realm of double helicenes. The absolute configuration of these PD8Hs was unambiguously confirmed by single-crystal X-ray diffraction analyses, revealing that the subtle configurational differences lead to great variation in the superhelical structure and molecular packing arrangement. Due to the embedding of the PDI chromophore, the PD8Hs possess outstanding fluorescence quantum yields of approximately 30%. Two pairs of enantiomers were resolved by chiral HPLC, and the chiroptical properties were evaluated using circular dichroism and circularly polarized luminescence spectroscopy, of which PD8H-6R exhibited excellent chiroptical performances in both the absorption and emission ranges with dissymmetry factors |gabs| of 0.012 and |glum| of 0.002.