Spatial disposition of dye molecules within metal oxide nanotubes

Donor/acceptor systems for electron and energy transfer are fabricated within modified multilayer nanotubes by taking advantage of the precise layering of the surface sol-gel method. Molecular thick layers of dye-embedded metal oxides were successively fabricated on the pore of anodized aluminum oxide (AAO) membrane, and multilayered nanotubes were formed after removal of the AAO template by alkali treatment. The efficiency of interlayer electron/energy transfer was strongly dependent on the distance of the two, and an adequate number of layers of zirconia was sufficient to functionally separate the two active layers. Electron transfer from an immobilized rhodamine B unit to the inner titania layer was prevented by the three zirconia layers as a 2.8 nm thick spacer. On the other hand, five layers of zirconia (4.7 nm) effectively prevented energy transfer from the fluorescamine-embedded outer layer to the rhodamine-B-isothiocyanate-embedded inner layer, in agreement with the quenching radius of the system. These spatially designed nanotubes will be a useful tool for fabricating novel molecular devices.