Chiroptical properties of poly(phenylacetylene)s: Experimental observation and theoretical calculation

The chiroptical properties of poly(phenylacetylene) (PPA) are investigated to provide a possible explanation for the optical activity with the aid of Drieding force field calculations. Calculations show that the PPA backbone can form helical structure in the trans-transoidal (t-t) and cis-(cisoidal) (c-c) configurations. The backbone in the cis-transoidal (c-t) and trans-cisoidal (t-s) configurations, however, takes a screw-like non-planar helical structure with phenyl rings spirally rotating around the polymer backbone. The c-t configuration has the lowest energy among the four possible configurations, implying that the observed optical activity in PPAs contributes mainly from c-t configuration.