Optically Active Polysilanes. Ten Years of Progress and New Polymer Twist for Nanoscience and Nanotechnology

Abstract

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.

Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

“…In the last two decades, we have designed and synthesized a wide range of polysilanes comprising chiral and/or achiral side groups. [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] MF realized that polysilanes were gifted with unique features of exhibiting intense and sharp UV absorption, circular dichroism (CD), and photoluminescence (PL) spectra around 300-400 nm, characteristic of the r-conjugation in the helical silicon-catenated main chain. Individual rod-like helical polysilanes in solution afford a highly intense, narrow exciton absorption band along with a sharp mirror-imaged emission band.…”

Mirror Symmetry Breaking in Helical Polysilanes: Preference between Left and Right of Chemical and Physical Origin

“…Although conclusive results using common chemical substances and apparatuses have not yet been reported, these modern MPV theories and current experimental reports, though still controversial, stimulated the author to revisit the equality and inequality of several ambidextrous artificial helical Si-Si bonded polymer-polysilanes-in solution as a function of temperature [71,72]. In a previous communication, the author reported preliminary testing results, implicating a possibility of detecting subtle differences in chiroptical and achiral 29 Si-NMR and viscometric data for a pair of helical polysilanes [73].…”

A dynamic supramolecular polymer with stimuli-responsive handedness for in situ probing of enzymatic ATP hydrolysis

“…H elically organized polymeric [1][2][3] and supramolecular [4][5][6][7] assemblies have been the subject of considerable interest as biomimetic systems to understand and appreciate asymmetric preferences like homochirality in nature. Typical designs of helical assemblies consist of optically active monomers, which bias the handedness during the (supramolecular) polymerization process [8][9][10][11][12][13][14][15][16][17][18][19] .…”