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.