Nanoclays: Two-dimensional shuttles for rare earth complexes in aqueous solution

Abstract

Nanoclays are shown to be attractive substrates in at least two major respects. Firstly, Hectorite analogous commercial clays (“Laponite”) can facilitate the usage of luminescent rare earth ions in aqueous solution, as their adherence to the clay surface strongly reduces water coordination and thus enables dramatically improved emission intensities. This also holds true for complexes of Tb 3+, which coordinate water in their native crystalline state, as demonstrated for tris(bipyiridine) complexes. For these, the laponite interaction affords a 16-fold gain in emission intensity in aqueous solution over the dissolved complex. Secondly, the two-dimensional, disk-like morphology of the clays enables a sufficient proximity of Ce 3+ and Tb 3+ to allow an energy transfer even at comparably low solution concentrations. In partially laminated, solid powders the efficiencies of the corresponding interlayer species decrease due to intimate interactions with the surrounding silicate and interlayer water, which can, however be counteracted by keeping the disks apart with long-chain, alkylammonium cations as spacers between the disks.