A series of polyrotaxanes containing alpha-cyclodextrin and naphthalene-modified alpha-cyclodextrin and solvent effects on the fluorescence quenchingby terminal units

Photoquenching systems were constructed using polyrotaxane in which cyclode xtrin (CD) rings of alpha -CD and 6-deoxy-6-(-naphthalene-2-sulfonyl)-alpha -cyclodextrin (NpCD) are threaded by a poly(ethylene glycol) chain with tr initrophenyl (acceptor) units at both ends (8-12). The effects, of the comp onent ratio of the polyrotaxanes on the naphthalene fluorescence quenching efficiency and energy migration between naphthalene units were examined by steady-state and time-resolved spectra and anisotropy measurements. The que nching efficiency of 8, which has the lowest content of NpCD, is larger tha n those of the polyrotaxanes with higher NpCD contents; however this tenden cy depends on the solvents. We explain the quenching mechanism of naphthale ne fluorescence by the combination process of Forster type energy transfer and electron transfer to the trinitrophenyl units.