Strongly Luminescent Palladium(0) and Platinum(0) Diphosphine Complexes

The synthesis, structure, and photoluminescence of palladium(0) and platinum(0) complexes containing biarydiphosphines, biphep (biphep = 2,2‘-bis(diphenylphosphino)-1,1‘-biphenyl) and binap (binap = 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl) have been studied. X-ray structure analysis of [Pt(biphep)₂] revealed the distorted-tetrahedral geometry of the complex. The photophysical properties of the three complexes [Pd(biphep)₂], [Pt(biphep)₂], and [Pd(binap)₂] were investigated and compared with that of the previously reported [Pt(binap)₂] complex. The [Pd(biphep)₂] complex shows the strongest luminescence with a high quantum yield (38%) and a long lifetime (3.2 μs) in a toluene solution at room temperature. The luminescence should be due to metal-to-ligand charge transfer excited states. At room temperature, radiative rate constants of the four complexes show similar values. The difference in the luminescent properties should reflect the different nonradiative rate constants of the complexes. The temperature-dependence of the luminescence spectra and lifetime of the complexes were also discussed.