Surface Modification of Layered Polysilane with n-Alkylamines, α,ω-Diaminoalkanes, and ω-Aminocarboxylic Acids

Surface modification of a layered polysilane consisting of two-dimensional crystalline silicon layers was investigated using n -alkylamines, α,ω-diaminoalkanes, and ω-aminocarboxylic acids. All products of the reactions with n -butyl- to n -hexadecylamines were dispersed as nanosheets in chloroform and exhibited the same blue light emission and photoluminescence spectra when exposed to UV light. After removal of the solvent, these products formed regularly stacked structures with an interlayer distance that increased in proportion to the alkyl length. The structure consists of bilayered alkyl chains with a tilt angle of ca. 47°. When the layered polysilane was reacted with α,ω-diaminoalkanes, the products were not dispersed in chloroform, because the silicon layers were covalently bonded by the diamines. The interlayer distances for these products also increased in proportion to the alkyl length. The layered polysilane was also successfully reacted with 12-aminododecanoic acid in pyridine or other polar solvents, where the formation of Si—N bonds was confirmed by Si K-edge X-ray absorption near-edge structure analysis. This result indicates that a highly reactive carboxyl group can be introduced onto the silicon layer surface. A chloroform solution of the 12-aminododecanoic acid-modified polysilane exhibited the same blue light emission as the polysilane modified with n -alkylamines.