An Ultralong Low-Temperature Phosphorescent Pentagonal-Prismatic Organometallic Cylinder Featuring Pentaphenylpyrrole-N-Heterocyclic Carbenes

A pentagonal-prismatic cylinder [Ag-5(L)(2)](PF6)(5) obtained from the pentaphenylpyrrole-bridged pentaimidazolium salt H-5-L(PF6)(5) and Ag-I ions was determined by X-ray diffraction analyses. The target organometallic cylinder not only exhibited enhanced fluorescence emission in dilute solution at room temperature but also showed an improved phosphorescence ratio compared with the free precursor and maintained a long lifetime (1.39 s) in the solid state at 77 K. Furthermore, the experimental results and DFT calculations confirmed that the formation of the organometallic cylinder promoted intersystem crossing. Meanwhile, the frontier orbitals of [Ag-5(L)(2)](PF6)(5) showed the main contribution of building block PPP as the luminescence source of [Ag-5(L)(2)](PF6)(5) by a modest heavy-atom effect. These results provide a strategy for constructing enhanced phosphorescent emission and long lifetime organometallic supramolecular phosphorescent materials.