Application of neutral d super(10) coinage metal complexes with an anionic bidentate ligand in delayed fluorescence-type organic light-emitting diodes

A series of heteroleptic coinage metal(i) complexes [Cu(PP)(PS)] 1, [Ag(PP)(PS)] 2, and [Au(PP)(PS)] 3 [PP = 1,2-bis(diphenylphosphino)benzene and PS super(-) = 2-diphenylphosphinobenzenethiolate] were synthesized. X-ray crystallography demonstrated that 1-3 possessed tetrahedral structures containing two types of bidentate ligands, PP and PS super(-). Photophysical studies and time-dependent density functional theory calculations indicated that the emission from 1-3 in the solid state at room temperature originated from thermally activated delayed fluorescence (TADF). The thiolate ligand with strong electron-donating character (PS super(-)) reduced the contribution from metal orbitals to the highest occupied molecular orbitals of the complexes, decreasing the metal-to-ligand charge-transfer character of the excited states of 1-3. The origin of TADF in 1-3 was attributed to ligand-to-ligand charge-transfer on the basis of molecular orbital calculations. Au(i) complex 3 was unstable in solution because of a rapid ligand exchange reaction, and Ag(i) complex 2 showed limited solubility in organic solvents. Cu(i) complex 1, which exhibited efficient green TADF with a maximum emission wavelength of 521 nm and a quantum yield of 0.52 in the solid state, was used to fabricate TADF-type organic light-emitting diodes viaa wet process.