Helical Polyacetylene-Based Switchable Chiral Columnar Phases: Frustrated Chain Packing and Two-Way Shape Actuator.

Chiral columns formed by a helical cis-polyphenylacetylene (PPA) derivative P1 are reversibly switched during a phase transition between two chiral columnar phases: the frustrated Φh (3D-SL) phase containing four chains at low temperature and a hexagonal columnar phase Φh at high temperature, accompanied by a simultaneous conformational change. The helix-helix transition along the PPA backbone during the Φh (3D-SL) -Φh transition makes the uniaxially oriented P1 capable of reversibly and reproducibly elongating (132 %) upon heating and contracting upon cooling, exhibiting the behavior of a two-way shape actuator.