Control of magnetism by isomerization of intercalated molecules in organic–inorganic hybrid systems

Intercalation of an organic photochromic molecule into layered magnetic systems has a possibility to provide multifunctional properties such as photomagnetism. In order to build up photosensitive multifunctional magnets, organic–inorganic hybrid systems coupled with photochromic diarylethene ion (DAE) and layered ferromagnets such as cobalt layered hydroxides (LDHs) and layered perovskite-type copper halides were synthesized. In the case of cobalt LDHs with DAE, Co4(OH)7(DAE)0.5·3H2O, the remarkable enhancement of the Curie temperature from 9 to 20 K was realized by substituting the open form of DAE with the closed form of DAE as intercalated molecule because of the delocalized π electrons in the closed form of DAE. By UV irradiation at 313 nm, Co4(OH)7(DAE)0.5·3H2O shows the photoisomerization of DAE from the open form to the closed one in the solid state, which induces the enhancement of the Curie temperature. In the case of layered perovskite-type copper chlorides with a diarylethene cation (DAE)CuCl4 with the open form of DAE, this shows the antiferromagnetic transition at TN = 3 K, while (DAE)CuCl4 with the closed form of DAE shows no magnetic phase transition above 2 K.