Fluorescent Cyclodextrins Responsive to Molecules and Metal Ions. Fluorescence Properties and Inclusion Phenomena of Nα-Dansyl-l-lysine-β-cyclodextrin and Monensin-Incorporated Nα-Dansyl-l-lysine-β-cyclodextrin

N α -Dansyl- l -lysine-β-cyclodextrin with a monensin unit ( 1 ) was prepared as a fluorescent chemosensor for molecule recognition. Its fluorescence properties and inclusion phenomena were examined using N α -dansyl- l -lysine-β-cyclodextrin ( 2 ) and N ε -benzyloxycarbonyl- N α -dansyl- l -lysine-β-cyclodextrin ( 3 ) as reference compounds. The fluorescence peak intensities of these hosts are in the order 2 > 1 > 3, suggesting that the dansyl unit of 2 is most deeply included in the β-cyclodextrin cavity. The host 1 exhibits two lifetimes, both in the absence of a guest [18.2 ns (81.8%) and 10.9 ns (18.2%)] and in the presence of 1-adamantanol (0.3 mM) [16.3 ns (17.8%) and 9.4 ns (82.2%)], demonstrating that 1 exists predominantly as a self-inclusion form with a longer lifetime and that it excludes the dansyl moiety to outside the cavity upon guest accommodation. A sodium cation in a solution of 1 enhanced the binding ability of 1 and increased the guest-dependent fluorescence variation. All of these results demonstrate that the monensin moiety of 1 is effective in changing the environment around the cyclodextrin cavity by forming a ring-like conformation with a sodium ion in the center.