Selective modification of the channel entrances of zeolite L with triethoxysilylated coumarin

The insertion of a triethoxysilylated coumarin dye into the channels of zeolite L from CH2Cl2 was examined. Fluorescence from the dye was observed only at the base planes of the cylindrical zeolite L crystals, indicating selective modification of the channel entrances. Leaching of the dye was observed when the material was dispersed in ethanol immediately after the insertion, suggesting reversibility of adsorption. A stable material was obtained after refluxing in toluene. This procedure led to the formation of covalent siloxane bonds between the triethoxysilyl group and silanol groups at the entrances of the zeolite channels. Hence, selective modification of the channel entrances is achieved via consecutive insertion and covalent bond formation processes. An appropriate choice of solvent for the insertion step is crucial. When zeolite L crystals containing pyronine were modified with the triethoxysilylated coumarin and irradiated at 335 nm, energy transfer from the coumarin to pyronine was observed.