Defect-free one-handed contracted helical tubular ladder polymers with a π-electron-rich cylindrical helical cavity were synthesized by alkyne benzannulations of the random-coil precursor polymers containing 6,6´-linked-1,1´-spirobiindane-7,7´-diol-based chiral monomer units. The resulting tightly-twisted helical tubular ladder polymers showed remarkably high enantioseparation abilities toward a variety of chiral hydrophobic aromatics with point, axial, and planar chiralities. The random-coil precursor polymer and analogous rigid-rod extended helical ribbon-like ladder polymer with no internal helical cavity exhibited no resolution abilities. The molecular dynamics simulations suggested that the π-electron-rich cylindrical helical cavity formed in the tightly-twisted tubular helical ladder structures is of key importance for producing the highly-enantioseparation ability, by which chiral aromatics can be enantioselectively encapsulated by specific π–π and/or hydrophobic interactions.
Carbyne, an elusive sp-hybridized linear carbon allotrope, has fascinated chemists and physicists for decades. Due to its high chemical reactivity and extreme instability, carbyne was much less explored in contrast to the sp2-hybridized carbon allotropes such as graphene. Herein, we report the on-surface synthesis of a polyynic carbon chain with ~40 alkyne units (80 carbon atoms), exhibiting the longest polyyne synthesized and characterized to date as a model for carbyne. The polyynic structure of carbon chains with alternating triple and single bonds is unambiguously revealed by bond-resolved atomic force microscopy, and the decoupled polyynic carbon chain exhibits a band gap of 3.67 eV measured by scanning tunneling spectroscopy. Our results provide a feasible route for the synthesis of long and stable polyynic carbon chains, leading a way to the final preparation of carbyne.
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