Evidence for Encaging Luminescent Guest Molecules in the Inner Cages of Zeolite Host

Clear evidence for encaging guest molecules in a host material was obtained for FAU-type zeolite containing fluorescein (FL) as a guest by employing the luminescence-quenching phenomenon of FL with C60. Whereas fluorescence of FL molecules adsorbed on the outer surface of the zeolite was effectively quenched as well as that in a homogeneous solution, that of the most FL molecules in the cages of the zeolite did not suffer from quenching by C60, giving clear evidence that FL molecules are located in the inner cages, which are inaccessible to C60. Only the fluorescence of the FL molecules located in the cages in the outermost unit cells of the zeolite was partially quenched. This partial quenching can be understood by considering the structure of the zeolite and the critical distance of electron transfer inducing the fluorescence quenching.