Synthesis and Metal Binding Properties of Anthraquinone Bridged with Coumarin

Abstract

Molecular switching in macrocyclic polyether systems has been the subject of intense study during the past 30 years. Especially, photochemical switching has been well-studied by Shinkai, Ueno, Takagi, Tabushi, and others.1 In addition, changes in pH,2 light3 and oxidation-reduction chemistry4 have all been explored as switching mechanisms. The lariat ethers,5 podands having nitroaromatic sidearms6 and similar species derived from anthraquinones have been concerned with electrochemical switching. Especially the anthraquinone system is an interesting one for the study of reducible and switchable lariat ethers7 because its anion is stable for months in water so long as oxygen is excluded.8 Although podands (noncyclic polyethylene glycols) gener-ally exhibit poor cation binding, when combined with the semiquinone nucleus, very strong cation complexation i