Photoresponsive Molecular Tweezers. Photoregulated Ion Capture and Release Using Thioindigo Derivatives Having Ethylenedioxy Side Groups

Article abstract of DOI:10.1021/ja00290a045

Two trans-cis photoisomerizable thioindigos having CH3OCH2CH2OC(O) or CH3O(CH2CH2O)3C(O) side groups at the 7 and 7' positions, T-1 and T-2, respectively, were synthesized with the aim of controlling the following three functions for achieving fully photoregulated ion transport across a liquid membrane: (1) "all or nothing" type metal ion binding ability, (2) binding ability not only for alkali-metal ions but also for soft metal ions, and (3) photocontrol by visible light.Solvent extraction of metal ions with T-1 revealed that the trans form had no binding ability to any of the metal ions, whereas K⁺, Rb⁺, and Na⁺ were selectively extracted (Na⁺ < Rb⁺ < K⁺) by the photogenerated cis form.The cis form, in addition, had high binding ability to Ag⁺, Hg⁺, Hg²⁺, and Cu²⁺ in comparison to alkali-metal ions.Ion transport experiments across a liquid membrane showed that repeating the cycles of alternate photoirradation of 529- and 488-nm light, which caused isomerization of T-1 from the trans to the cis form (529 nm) and from the cis to the trans (488 nm), resulted in the transportation of Ag⁺ from aqueous phase I to II through a 1,2-dichloroethane membrane containing T-1.