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

A new synthetic route to polysilylenes is reported which allows access to h itherto inaccessible heteroatom-substituted poly(dialkoxysilylene)s. Perchl oropolysilane, (SiCl2)(n), undergoes substitution by alcohols in the presen ce of an amine to yield monomodal poly(dialkoxysilylene)s with molecular we ights (M-w) up to 62 000, ultraviolet (UV) absorption maxima due to the low est energy sigma-sigma* transition of the silicon backbone in the range 336 -347 nm (red-shifted compared to dialkyl analogues), and fluorescence emiss ion 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 pr ediction of the reduction of the optical band gap due to interaction betwee n silicon (sigma) and oxygen lone pair (n) orbitals is confirmed.