Syntheses and Chiroptical Properties of Optically Active Helical Poly(phenylacetylene)s Bearing [60]Fullerene Pendants

Two novel C 60 -bound chiral ( 3 ) and achiral ( 2 ) phenylacetylenes were synthesized by the treatment of C 60 with ( R )- N -[1-(4-ethynylphenyl)ethyl]glycine and N -(4-ethynylbenzyl)glycine by the Prato reaction in the presence of paraformaldehyde and dipentadecyl ketone, respectively. The homopolymerization of the achiral 2 bearing long alkyl chains and copolymerization with optically active phenylacetylenes including 3 using a rhodium catalyst in chloroform homogeneously occurred, giving the C 60 -containing helical poly(phenylacetylene)s soluble in chloroform, while the homopolymers of the analogous achiral C 60 -bound phenylacetylenes with no alkyl chain ( 1 ) and 3 were totally insoluble in common organic solvents. The obtained copolymers exhibited an induced circular dichroism (ICD) both in the main-chain region and in the fullerene chromophoric region, indicating that the optically active copolymers possess a preferred-handed helical conformation and that the pendant fullerene groups are arranged in helical arrays with a predominant screw-sense along the polymer backbones. The formation of a hierarchical supramolecular assembly of the homopolymers of 1 and 3 bearing fullerene pendants on each repeating unit was also studied by electron microscopy.