Synthesis of a Single PbSe Magic-Sized Cluster: Insights into Reaction Kinetics, Atomic Structure, and Optical Properties.

Abstract

PbSe magic-sized clusters (MSCs), characterized by their homogeneous sizes and sharp absorption features, represent an important class of nanomaterials for precise structure-property correlation. However, their synthesis is complicated by the formation of mixtures of MSCs. Here, we report the facile synthesis of a single PbSe MSC with an absorption peak at 625 nm (PbSe-625 MSC). This is achieved through the rapid conversion of reaction precursors at the nucleation stage, leaving no residual PbSe monomers to power the continuous growth of the next MSC. Specifically, by using a highly reactive diphenylpropylphosphine selenide (DPPrSe) along with excess diphenylphosphine (DPP) to react with Pb(oleate)₂ in anhydrous pentane, the reaction was complete within half an hour, yielding the PbSe-625 MSC. In situ absorption spectra provide insights into the nucleation and growth kinetics, showing that phosphine selenide precursors, DPP concentration, and solvents are crucial for producing the PbSe MSC. The facile synthesis is highly reproducible, enabling a relatively scaled-up (∼70 mg) production of the cluster for further characterization. The PbSe-625 MSC exhibits a strong emission peak at ∼800 nm with an absolute quantum yield of 25-35%. By comparing the experimental powder X-ray diffraction pattern and the simulated patterns from various structural models, together with X-ray photoelectron spectroscopic studies, the PbSe-625 MSC is likely to be a Pb₇₉Se₄₄ species with a rock salt phase and a truncated octahedron shape. Our method provides important insights into the kinetic control of the single-sized PbSe clusters and the derivation of their atomic structures.