Helical Polybissilsesquioxane Bundles Prepared Using a Self-Templating Approach

Polybissilsesquioxanes with single-handed helical morphologies attracted much attention during the last decade, which could be applied as asymmetric catalysts and chiral stationary phases. Herein, a pair of chiral biphenylene-bridged bissilsesquioxanes were synthesized. They self-assembled into helical bundles in ethanol, behavior that was confirmed in field emission scanning electron microscopy images. Circular dichroism analysis indicated that the biphenylene groups twisted in a single-handed fashion. Single-handed helical polybissilsesquioxane bundles were prepared via polycondensation of the bissilsesquioxanes, using a self-templating approach. Because of the shrinkage that occurred during polycondensation, the helical pitches of the bundles were shorter than those of their corresponding organic self-assemblies. The wide-angle X-ray diffraction pattern indicated that there were no π-π interactions among the diphenylene groups. The circular dichroism spectra indicated that the chirality was successfully transferred from the bissilsesquioxane self-assemblies to the polybissilsesquioxane. The polybissilsesquioxanes displayed a capacity for the adsorption of nitrobenzene and had potential application for enantioseparation.