Temperature-induced chiroptical changes in a helical poly(phenylacetylene) bearing N,N-diisopropylaminomethyl groups with chiral acids in water.

A stereoregular poly(phenylacetylene) bearing an N,N-diisopropylaminomethyl group as the pendant (poly-1) changed its structure into the prevailing one-handed helical conformation upon complexation with optically active acids in water. The complexes exhibited induced circular dichroism (ICD) in the UV/Vis region of the polymer backbone. Poly-1 is highly sensitive to the chirality of chiral acids and can detect a small enantiomeric imbalance in these acids, in particular, phenyl lactic acid in water. For example, a 0.005% enantiomeric excess of phenyl lactic acid can be detected by CD spectroscopy. The observed ICD intensity and pattern of poly-1 were dependent on the temperature and concentration of poly-1, probably due to aggregations of the polymer at high temperature as revealed by dynamic light scattering and AFM. On the basis of the temperature-dependent ICD changes, the preferred chiral helical sense of poly-1 was found to be controlled by noncovalent bonding interactions by using structurally different enantiomeric acids.