CATION COMPLEXATION, PHOTOCHROMISM, AND REVERSIBLE ION-CONDUCTING CONTROL OF CROWNED SPIRONAPHTHOXAZINE

A spironaphthoxazine derivative incorporating a monaza-12-crown-4 moiety at the 5'-position has been designed as a light-resistant, cation-complexable photochromic compound. Complexation of alkali metal ions by the crown moiety in the crowned spironaphthoxazine allows the spironaphthoxazine skeleton to isomerize to its corresponding open colored form, even under dark conditions. Specifically, Li+ complexation greatly stabilizes the open colored form due to the intramolecular interaction between its oxo group and crown-complexed cation, as well as the selective Li+ complexation of its 12-crown-4 moiety. Taking advantage of the high Li+ selectivity in the cation-induced isomerization of crowned spironaphthoxazine, the thermal stability of the open colored form can be modulated continuously by added Li+ concentrations. Even in the presence of the metal ion, UV- and visible-light irradiation led to further isomerization to the open form and back-isomerization to the initial closed form, respectively. Photoisomerization of crowned spironaphthoxazine to its open form promoted Li+ binding due to the additional axial interaction with the crown-complexed Li+, while that back to the closed form attenuated the cation binding. The photoinduced change in the cation-binding ability of crowned spironaphthoxazine, which possesses high light-fatigue resistance, has led to a highly reversible, photochemical switching system of ionic conduction.