Cation recognition with fluorophore crown ethers

The fluoroionophore behavior of various macrocycles with oxygen and nitroge n donors was reviewed in the present paper, and the cationic recognition of alkali and alkaline-earth metals involving different photophysical effects depending on the fluoroionophore structures was summarized. Spectrofluorom etry is a very sensitive technique measuring both emission and excitation i ntensities of a fluorescent molecule that is influenced by the environment. The cationic recognition of fluoroionophore crown ethers which possess at least two molecular components with sites that interact with photons as wel l as ions is studied. Cations mostly induce the changes in triplet energy r elative to the excited singlet state, S-1 --> T-1, and the ground state, T- 1 --> S-0. In the presence of metal cations, the increased phosphorescence lifetime of luminescent macrocycles, in general, gave complexation-enhanced quenching fluorescence spectra that reduce the fluorescence lifetime. Howe ver, if the phosphorescence lifetime is reduced, the fluorescence life is i ncreased and the complexation-enhanced fluorescence spectra would be observ ed. Optical responses originating from the different photophysical mechanis ms of photoinduced charge transfer, electronic energy transfer, monomer/exc imer equilibrium, and internal charge transfer were represented. The recent studies an the cation recognition of fluorophore macrocyclic ethers are ex emplified and discussed in the present paper.