Cation complexation, isomerization, and photoresponsive ionic conduction of a crown ether derivative carrying two spirobenzopyran units

Cation complexation and subsequent isomerization of a diaza-18-crown-6 derivative possessing two spirobenzopyran units, crowned bis(spirobenzopyran), were investigated in solution and compared with those of its corresponding derivative incorporating only one spirobenzopyran unit. Complexation of multivalent metal ions, especially Ca2+ and La3+, by crowned bis(spirobenzopyran) enhanced the isomerization of the spirobenzopyran moiety to the corresponding merocyanine form due to the effective intramolecular interaction between a crown-complexed cation and two phenolate anions in the cation complexes of the merocyanine form. Significant photoinduced switching of ionic conductivity was realized in composite films containing crowned bis(spirobenzopyran) and a calcium salt.