Inspired by biological helices (e.g., DNA), artificial helical polymers have attracted intense attention. However, precise synthesis of one-handed helices from achiral materials remains a formidable challenge. Herein, a series of achiral poly(biphenyl allene)s with controlled molar mass and low dispersity were prepared and induced into one-handed helices using chiral amines and alcohols. The induced one-handed helix was simultaneously memorized, even after the chiral inducer was removed. The switchable induction processes were visible to naked eye; the achiral polymers exhibited blue emission (irradiated at 365 nm), whereas the induced one-handed helices exhibited cyan emission with clear circularly polarized luminescence. The induced helices formed stable gels in various solvents with helicity discrimination ability: the same-handed helix gels were self-healing, whereas the gels of opposite-handed helicity were self-sorted. Moreover, the induced helices could separate enantiomers via enantioselective crystallization with high efficiency and switchable enantioselectivity.
In this work, helical polycarbenes
with optical activity were designed
and facilely synthesized through the helix-sense-selective polymerization
(HSSP) of the diazoacetate monomer with a dimethylbenzyl ester pendant
catalyzed by π-allylPdCl with chiral phosphine ligands at room
temperature. The polymerization was carried out in a living and controlled
style, and a range of helical polycarbenes with the desired number-average
molecular weights and narrow molecular weight distributions were obtained.
Circular dichroism and UV–vis analyses revealed that these
polycarbenes exhibited a stable helical conformation with a preferred
handedness, and their helical directions were dependent on the chirality
of the chiral phosphine ligands. Further studies showed that the helical
conformation of the obtained polycarbenes was from the polymeric backbone
rather than the intermolecular aggregation in the solutions. Moreover,
the prepared, optically active, helical polycarbenes possessed excellent
enantioselective crystallization ability for threonine racemates.
The enantiomeric excess (e.e.) of the induced crystals could be up
to 83% via utilizing the prepared helical polycarbenes as a chiral
separation agent.
Inspired by biological helices (e.g., DNA), artificial helical polymers have attracted intense attention. However, precise synthesis of one‐handed helices from achiral materials remains a formidable challenge. Herein, a series of achiral poly(biphenyl allene)s with controlled molar mass and low dispersity were prepared and induced into one‐handed helices using chiral amines and alcohols. The induced one‐handed helix was simultaneously memorized, even after the chiral inducer was removed. The switchable induction processes were visible to naked eye; the achiral polymers exhibited blue emission (irradiated at 365 nm), whereas the induced one‐handed helices exhibited cyan emission with clear circularly polarized luminescence. The induced helices formed stable gels in various solvents with helicity discrimination ability: the same‐handed helix gels were self‐healing, whereas the gels of opposite‐handed helicity were self‐sorted. Moreover, the induced helices could separate enantiomers via enantioselective crystallization with high efficiency and switchable enantioselectivity.
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