Polysilanes poly aggregates

The recent interest in substituted silane polymers has resulted in a number of theoretical (15-19) and spectroscopic (19-21) studies. Most of the theoretical studies have assumed an all-trans planar zig-zag backbone conformation for computational simplicity. However, early PES studies of a number of short chain silicon catenates strongly suggested that the electronic properties may also depend on the conformation of the silicon backbone (22). This was recently confirmed by spectroscopic studies of poly(di-n-hexylsilane) in the solid state (23-26). Complementary studies in solution have suggested that conformational changes in the polysilane backbone may also be responsible for the unusual thermochromic behavior of many derivatives (27,28). In order to avoid the additional complexities associated with this thermochromism and possible aggregation effects at low temperatures, we have limited this report to polymer solutions at room temperature. 

Figure 4.27 (a) CD and UV spectra of poly n-hexyl(p- -propoxyphenyl)silane (41) aggregates in toluene/(5> (a solid line) or (R)-2-butanol (b dotted line)/methanol mixtures at 20°C and (.b) plot of CD intensities at 354 nm of the polysilane aggregates in toluene/various ratio of (5)/(i )-2-butanol/methanol mixtures at 20°C. 

In order to further experimentally probe the hard-core model of polysilane aggregate chirality, a series of poly-[(alkyl)alkylphenylsilylene]s, differing in phenyl ring-substituent position and chain length were synthesized, designed such that the polymer chain diameter, d, and helical pitch, p, in the hard-core model were varied.343... 

A novel approach to aggregate control was described by Terao et al., who confined optically active polysilanes inside poly(ureaurethane) microcapsules and then induced aggregation at 20 and — 78 °C by addition of the polysilane-containing microcapsules to THF or ethanol. 5... 

The present knowledge and understanding of 1 may help us to elucidate chiroptical amplification of other optically active polysilanes in isotropic dilute solution, as aggregate forms dispersed in solution, and in a solid film. Indeed, poly(methyl-(-)-/9-pinanylsilane) ((+)-7 Mw = 10200) prepared by Aoki, Oikawa and coworkers showed a bisignate Cotton CD band at 280 and 303 nm, associated with a broad UV absorption at 300 nm in chloroform at... 

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