Selective transport of alkali-metal cations through liquid membranes by non-cyclic carriers

The emission spectra of a series of naphthalene end-labeled oligo-oxyethylene (N-P-n-N) and their facilitated transport of cations across liquid membranes have been investigated. Alkali-metal cations enhance or inhibit the intramolecular excimer formation of N-P-n-N remarkably, suggesting that the polyether chain of N-P-n-N in solution complexes with the cations, and the orientation of the terminal chromophores depends on the cation size mid the length of the polyether chain. These compounds are able to act as carriers to facilitate transport of alkali-metal cations through organic liquid membranes. The transport efficiencies are comparable with those of cyclic carriers such as crown ethers, and show remarkable selectivity.