Cation recognition with fluorophore crown ethers

The fluoroionophore behavior of various macrocycles with oxygen and nitrogen 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. Spectrofluorometry is a very sensitive technique measuring both emission and excitation intensities 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 well as ions is studied. Cations mostly induce the changes in triplet energy relative 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. However, if the phosphorescence lifetime is reduced, the fluorescence life is increased and the complexation-enhanced fluorescence spectra would be observed. Optical responses originating from the different photophysical mechanisms of photoinduced charge transfer, electronic energy transfer, monomer/excimer equilibrium, and internal charge transfer were represented. The recent studies an the cation recognition of fluorophore macrocyclic ethers are exemplified and discussed in the present paper.