Thermotropic, Reversible, and Highly Selective One-Handed Helical Structure of Hydroxyl Group-Containing Poly(phenylacetylene)s and Its Static Memory

In the presence of achiral amine, polyacetylene (poly(1)) prepared using chiral phenylacetylene, with two hydroxyl groups (1), exhibited a unique reversible thermotropic one-handed twisting behavior at a critical twisting temperature (CTT). At lower temperatures, the main chain of poly(1) took a circular dichroism inactive cis-transoidal conformation in a mixture of hexane/achiral amine. However, when the system was heated to a temperature above the CTT, the main chain of poly(1) twisted into a one-handed helical cis-cisoidal conformation. Moreover, efficient chiral amplification based on this thermotropic twisting was also observed in a chiral/achiral copolyacetylene (copoly(1/2)) composed of chiral unit 1 and achiral unit 2, both having hydroxyl groups. The amplified helical chirality in the sequences of achiral unit 2 was memorized in the solid state. The copolymer's composition and the amine size affected the CTT of the system. The twisting mechanism and the effect of temperature, amine, and copolymer composition on the twisting behavior were then investigated.