Photocontrollable ion transport across a liquid membrane by anthracene end-labeled oligo-oxyethylenes

Abstract

The alkali-metal ion extraction from aqueous solution to organic phase and the ion transport across a liquid membrane facilitated by anthracene end-labeled oligo-oxyethylenes (A-P_n-A) and their photodimers have been investigated. The ion extraction equilibrium constants for the photodimers are 10–100 times greater than those for the monomeric form A-P_n-A. The non-cyclic monomers A-P_n-A are also able to act as carriers to facilitate transport of alkali-metal ions across an organic liquid membrane with moderate efficiency. Alternate irradiation of the membrane in contact with the source phase with light (λ > 300 nm) and that in contact with the receiving phase with light (λ < 300 nm) resulted in remarkable increase of ion transport selectivity and 6–10 times enhancement of the transport rate. These observations are interpreted in terms of the photoinduced interconversion between the dimeric and the monomeric forms of A-P_n-A which are responsible for the ion complexation and ion release in the overall transport process, respectively. Thus, we have broken the dilemma occurring in the ion transport system: the very stable complex which may rapidly extract an ion into the membrane phase, cannot release the ion efficiently from the complex.