Magically Pure CdSe Nanoclusters

Chemists have isolated stoichiometrically pure “magic sized” nanoclusters of the semiconductor cadmium selenide (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201202380). The straightforward method for preparing pure samples of (CdSe)₁₃, one of several cluster sizes deemed “magic” because of its high stability, may trigger a host of follow-up investigations into the nanoclusters’ structure, reactivity, and other properties, the researchers say. Discovery of unique and size-specific optical and electronic properties of semiconductor nanoclusters and nanocrystals has touched off a wave of research aimed at synthesizing stoichiometrically pure samples of those materials. Earlier spectroscopy studies suggested that specific-sized clusters may be ideal for select optoelectronic applications. Researchers have succeeded in preparing mixtures of magic-sized CdSe clusters, for example (CdSe)₃₃ and (CdSe)₃₄, but not pure samples. Now, a team led by Yuanyuan Wang and William E. Buhro of Washington University in St. Louis has shown that colloidal nanocluster-amine aggregates can be exfoliated, yielding sheets of octylamine-capped (CdSe)₁₃. A ligand-exchange step releases the sheet-bound clusters and produces pure samples of freely soluble oleylamine-capped (CdSe)₁₃, the team reports.