Layered inorganic-organic nanocomposites: Application to photofunctional materials and conversion to inorganic microporous materials

Layered inorganic-organic nanocomposites can be prepared by intercalation of organic compounds into various two dimensional inorganic compounds, such as clay minerals and layered polysilicates. Two different roles of organic guest species are described in the application of intercalation compounds to development of functional materials. The first case shows that organic substances with peculiar photochemical properties can be incorporated in the nanometer-scaled interlayer spaces. Luminescence behavior and photochemical hole burning (PHB) of layered inorganic-organic nanocomposites are investigated from the viewpoint of host-guest interactions. The luminescence maxima of intercalated Ru(bpy)₃²⁺ incorporated into fluor-tetrasilicic mica cointercalated with poly(vinylpyrrolidone) shifted gradually toward blue with the decrease in the loading of Ru(bpy)₃²⁺. Ru(bpy)₃²⁺ was effectively isolated to suppress self quenching due to aggregation even at its high concentration loading. 1,4-Dihydroxyanthraquinone which is known to show a PHB reaction was intercalated into a tetramethylammonium pillared clay mineral and persistent spectral zero-phonon hole was observed at liquid helium temperatures. In spite of the high concentration of 1,4-dihydroxyanthraquinone, a narrow hole was obtained with no distinct decrease in burning efficiency if compared with those doped in ordinary polar polymers or organic glasses. In the second case, intercalation of organic substances into a layered polysilicate induces the change of the layered structure to form a three-dimensional silicate network by condensation of silanol groups in adjacent layers. This phenomenon indicates that novel microporous materials with controlled pore sizes can be prepared through inorganic-organic nanocomposites.