Synthesis and spectroscopic characterization of heteroatom polysilylenes:: Poly(dialkoxysilylene)s and evidence for silicon σ-oxygen n mixing interaction

A new synthetic route to polysilylenes is reported which allows access to hitherto inaccessible heteroatom-substituted poly(dialkoxysilylene)s. Perchloropolysilane, (SiCl2)(n), undergoes substitution by alcohols in the presence of an amine to yield monomodal poly(dialkoxysilylene)s with molecular weights (M-w) up to 62 000, ultraviolet (UV) absorption maxima due to the lowest energy sigma-sigma* transition of the silicon backbone in the range 336-347 nm (red-shifted compared to dialkyl analogues), and fluorescence emission in the range 368-398 nm. Substitution with enantiopure chiral alcohols affords optically active polymers with matching UV and circular dichroism (CD) signals, indicating preferential screw sense helicity of the main chain, which is further investigated by force field calculations. Theoretical prediction of the reduction of the optical band gap due to interaction between silicon (sigma) and oxygen lone pair (n) orbitals is confirmed.