Preparation and characterization of the inclusion complexes of poly(dimethylsilane)s with cyclodextrins

beta-Cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD) formed inclusion complexes with poly(dimethylsilane)s (PSi) of various molecular weights to give crystalline compounds. However, alpha-cyclodextrin (alpha-CD) did not form complexes with PSi of any molecular weight. The yields of the beta-CD-PSi inclusion complexes decreased with increasing molecular weight of PSi. In contrast, the yields of the gamma-CD-PSi inclusion complexes increased with increasing molecular weight, reached a maximum at molecular weight of around 760, and gradually decreased at higher molecular weight. The chain-length selectivities are totally different between beta-CD and gamma-CD. The gamma-CD-PSi inclusion complexes are stoichiometric 1:3 (gamma-cyclodextrin:monomer unit of PS) compounds. The complexes were isolated and characterized by H-1 NMR, C-13 CP/MAS NMR, and X-ray diffraction studies. These results suggest that CDs form channel-type complexes with PSi. The optical properties were studied by ultraviolet absorption and fluorescence spectroscopy. The PSi main chain in the cavities of gamma-CD takes an all-trans conformation.