Synthesis and property of helical poly(phenylacetylene)s bearing chiral ruthenium complexes and real space imaging of meso- and nanoscopic structures by atomic force microscopy

Novel sets of helical poly(phenylacetylene)s bearing a chiral ruthenium (Ru) complex with opposite chirality (Delta and Lambda forms) as a bulky pendant (poly-1 and poly-2) were synthesized through the polymerization of the corresponding optically pure phenylacetylenes with a rhodium catalyst, and their structures in solution and morphology on solid substrates were investigated with NMR, ultraviolet-visible, and circular dichroism (CD) spectroscopies and with atomic force microscopy (AFM), respectively. The obtained cis-transoidal polymers (poly-1 and poly-2) showed characteristic Cotton effects in the region of metal-to-ligand charge transfer of the chiral Ru pendants. Poly-1 and poly-2 were thought to have a predominantly one-handed helical conformation induced by the chiral pendants. However, the apparent Cotton effects derived from the helically twisted pi-conjugated polymer backbone could not be observed, probably because of the strong chiral chromophoric pendants. However, in the AFM images, the helical polymers adsorbed on mica could be easily discerned as isolated strands, and the visualization and discrimination of the right- and left-handed helical structures of the chiral polymers were achieved by high-resolution AFM imaging. On the basis of the AFM observations together with the CD measurements and computational calculation results, possible structures of poly-1 and poly-2 were examined. (C) 2004 Wiley Periodicals, Inc.