Photoinduced adsorption of spiropyran into mesoporous silicas as photomerocyanine

By UV irradiation to a toluene solution of a spiropyran-containing suspended mesoporous silica particles, the photochemically formed photomerocyanine was adsorbed into the mesoporous silica to give a red-colored product, which is very stable for a long time at room temperature. The red color faded on visible light irradiation, indicating that photomerocyanine desorbed from the mesoporous silica to give a toluene solution of spiropyran. Bistability was achieved in the presence of two different chemical environments for the photochromic molecules: toluene, which stabilizes organophilic spiropyran, and mesoporous silica, which stabilizes hydrophilic photomerocyanine.