Thermal Activation of Asymmetry Amplification Effects in Helical Polymer-Metal Complexes

Dynamic helical polymers such as poly(phenylacetylene)s (PPAs) exhibit different asymmetry amplification effects, e.g., helix inversion or screw-sense induction, in the presence of different external stimuli such as temperature, solvents, or metal ions that usually operate independently through interaction with the pendant on the monomer repeating units (m.r.u.). In this work, we will demonstrate that the helical structure of a chiral PPA can be tamed by playing with two different external stimuli such as temperature and metal ions. Thus, when a metal ion salt is delivered to a chloroform solution of a chiral PPA to generate a chiral PPA (m.r.u.)/Mⁿ⁺ complex in a ratio of 1.0/<0.5 mol/mol, a temperature-responsive material is obtained. Interestingly, when the temperature is lowered to about 278-283 K, the metal ion uncomplexes, which recovers the initial helical structure adopted by the PPA. This complexation-decomplexation between the chiral PPA and the metal ions is fully reversible and triggers different asymmetry amplification effects-helix inversion, screw-sense induction or Sergeants-and-Soldiers (SaS), among others-, allowing the creation of a temperature-responsive helical polymer-metal complex (HPMC) from a metal-responsive helical polymer.