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)Pb(3)Bri(2) (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.
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