The first optically active polygermanes: preferential screw sense helicity of enantiopure chiral-substituted aryl polygermanes and comparison with analogous polysilanes

Circular dichroism and ultraviolet spectroscopic studies of meta and para poly[methyl{(S)-2-methylbutylphenyl}germane]s, the first enantiopure chiral substituted polygermanes, indicate that the polymer main chains are induced to adopt preferential screw sense helical conformations and the values of the Kuhn dissymmetry ratio (gabs,=Δε/ε) at −70 °C were evaluated as −0.34×10−4 and −0.38×10−4, respectively for the polymers above. The analogous polysilanes have gabs, values of −0.76×10−4 and −0.81×10−4, which indicate a greater preferential screw sense selectivity. It is suggested that the origin of the lower screw sense selectivity in the polygermanes lies in the longer EE bond in the backbone, leading to reduced steric interaction between the preferential screw sense-inducing enantiopure chiral side chain moieties.