Synthesis and Photoluminescence Properties of an Unprecedented Phosphinine–Cu4Br4 Cluster

A hitherto unprecedented polynuclear phosphinine–Cu(I) complex has been prepared and crystallographically characterized. The molecular structure in the crystal verifies the presence of the heterocubane-type tetrameric cluster [LCuBr]4 (L = 2,4-diphenyl-5-methyl-6-(2,3-dimethylphenyl)phosphinine), which unexpectedly shows in the solid state temperature-independent orange phosphorescence solely from an 3XMLCT state, in clear contrast to the well-established dual-emissive-state model for luminescent Cu4X4L4 clusters.