Bulk Assemblies of Lead Bromide Trimer Clusters with Geometry-Dependent Photophysical Properties

Single crystalline bulk assemblies of metal halide clusters show great potential as highly efficient light emitters with tunable photophysical properties. However, synthetic control of the geometry of the clusters in a rational manner has not been well established, and the relationships between the photophysical properties and structures of this emerging class of zero-dimensional materials are still not well understood. Here, we report the synthesis and characterization of two bulk assemblies of lead bromide clusters, (bmpy)₆[Pb₃Br₁₂] (T1) and (bmpy)₉[ZnBr₄]₂[Pb₃Br₁₁] (T2) (bmpy: 1-butyl-1-methylpyrrolidinium), which contain metal halide trimer clusters with different geometries. T1 with chain-shaped [Pb₃Br₁₂]^6– clusters is not emissive at room temperature, whereas T2 with triangle-shaped [Pb₃Br₁₁]^5– clusters exhibits yellowish-green emission peaked at 564 nm with a photoluminescence quantum efficiency of 7% at room temperature. Detailed analysis of the structural and photophysical properties show that the photophysical properties and excited-state dynamics of these materials are highly dependent on the geometry of the metal halide clusters.