Lanthanide complexes with more intense luminescence: a strategy for the formation of polymetallic lanthanide dendrimer complexes and semiconductor nanocrystal compounds

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (μs - ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. In order to obtain luminescence from lanthanide cations, the cation must be located at close distance to a suitable sensitizer ("antenna"). Two similar methods have been used in our group to develop more efficient lanthanide complexes based on a polymetallic approach to obtain lanthanide compounds with improved luminescence efficiency. The first method involves using dendrimers to combine multiple antennae groups and several lanthanide cations into the same discrete molecule. The second approach involves doping CdSe semiconductor nanocrystals with luminescent terbium cations to use the nanocrystal electronic structure as an antenna to sensitize lanthanide cations. Using nanocrystals as antennae provides a superior way to protect the lanthanide cations from non-radiative deactivations, while providing a variety of controlled donating energy levels. In both methods, it is possible to incorporate several lanthanide metal cations into each dendrimer or nanocrystal, thus increasing the number of emitters and the resulting luminescence intensity of the species.