Synthesis and chiroptical properties of helical poly(phenylacetylene) bearing optically active chiral oxazoline Pendants

The novel optically active (S)-4-benzyl-2-(ethynylphenyl)-oxazoline (BnEPhOx) was successfully prepared and polymerized using rhodium catalyst ([Rh(nbd)Cl]₂) to obtain the moderate molecular weight poly(phenylacetylene)s bearing chiral oxazoline derivatives with high yields (≥90%). The ¹H NMR spectra demonstrated that the resulting polymers had high stereoregular structures. Moreover, the poly(phenylacetylene)s bearing chiral oxazoline exhibited better thermal stability than poly(phenylacetylene). The resulting polymers showed higher absolute values of optical specific rotation than the monomer. The polymers also exhibited intense CD signal in the region of the π-π1 band of the conjugated polyacetylene backbone in chloroform solution. The results of specific rotation and CD spectroscopy indicated that all the polymers adopted higher-order structure with predominantly one-handed screw sense.In addition, the resulting polymers emitted fluorescence under UV irradiation.