Optically active polysilanes. Ten years of progress and new polymer twist for nanoscience and nanotechnology

Abstract

In the family of optically active synthetic polymers, optically active polysilanes, which comprise a helical main chain of silicon-silicon single bonds and chiral and/or achiral side groups, exhibit unique absorption, circular dichroism, and fluorescence spectra around 300-400 nm due to σ-conjugation. Since the first brief report of optically active polysilane synthesis in 1992, the field has now widened to include various homo- and copolymers of optically active poly(dialkylsilane)s, poly(dialkoxysilane)s, poly[alkyl(aryl)silane]s, and poly(diarylsilane)s. This review comprehensively covers work on (i) the relationship between side chain structure, (ii) local structure-global shape relationship, (iii) (chir)optical properties, (iv) (semi)quantitative population analysis of right- and left-handed helices based on Kuhn's dissymmetry ratio, (v) several helical cooperativity effects, (vi) molecular imaging, (vii) inversion of screw-sense, (viii) chiroptical switch and memory, (ix) transfer and amplification of molecular chirality to aggregates, (x) cholesteric liquid crystallinity, (xi) helical supramolecular structures, and (xii) latent helicity, as consequences of side group internal interactions and other external stimuli. Such knowledge and understanding may stimulate optically active polymer research in the realm of nanomaterial science and nanotechnology at the sub-nm level as well as traditional polymer science, and may advance these polymers to new functional nanomaterials and thence to the realization of nanodevices in the future.