Construction and Function of Supramolecular polvmers

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The main object of this study is construction of polyrotaxanes composed of cyclodextrin (CD) and modified CD as a novel copolymers, in which monomer units are connected together not by covalent bond but by supramolecular interaction. From this viewpoint, we prepared a series of polyrotaxanes, which have α-CD and naphthtalene-modified α-CD (NpCD) as monomer units and a poly (ethylene glycol) as a threading chain. The ratios of the NpCD unit in the polyrotaxanes are 20%, 60%, and 100 % when both ends of poly (ethylene glycol) have anthracene units as stoppers. We examined energy transfer from naphthalene units to anthracene units in the systems, in which naphthalene units may be expected to act as antenna units which absorb light. Light harvesting ability of the systems increased but energy transfer efficiency from the naphthalene units to anthracene ones decreased with increasing content of naphthalene unit in the polyrotaxane series. This system also revealed that fluorescence anisotropy decreases with increasing content of NpCD in the polyrotaxanes, informing that energy migration occurs and energy tends to be lost during the randomly occurring energy transfer. We also constructed another type of polyrotaxanes, in which trinitrophenyl units exist at both ends. We observed quenching of the naphthalene fluorescence in various solvent systems with different polarities and found that highly efficient energy transfer is attained in the solvent system of low polarity and antenna effect becomes remarkable with increasing content of naphthalene unit in the polyrotaxanes.