Synthesis of Novel Photochromic Calix[4]arene Ligand Bearing a Spirobenzopyran and Three Ethyl-Ester Moieties and Photocontrol of Its Alkali Metal Ion Extractability

Abstract

Abstract A novel photochromic calix[4]arene ligand bearing a spirobenzopyran and three ethyl-ester moieties (compound 1) was synthesized, and photocontrol of its alkali metal ion extractability was studied. In the dark, compound 1 showed the largest changes of absorption spectra for Na+ among alkali metal ions. When Na+ was gradually added to the solution of compound 1, its complexation behavior was evaluated by 1H NMR, which suggests that Na+ was taken into the cavity formed by four carbonyl oxygens and four ether oxygens, and that compound 1 formed a 1:1 complex with Na+. The proton signals originating from the spirobenzopyran moiety were slightly changed by metal-ion complexation. This means that the spirobenzopyran moiety was not very close to Na+ under dark conditions. Liquid–liquid extraction experiments with alkali metal ion using compound 1 made it clear that the extractability of Na+ was enhanced under UV-light irradiation, compared with that under visible-light irradiation. This suggests that the electrostatic interaction between a phenolate anion of the merocyanine moiety generated by UV-light irradiation and Na+ promotes the extractability to some extent.