Highly efficient green organic light-emitting diodes containing luminescent tetrahedral copper(I) complexes

A series of highly emissive sublimable copper(I) complexes with tetrahedral geometries, Cu(dppb)(pz(2)Bph(2)) 1, Cu(dppb-F)(pz(2)Bph(2)) 2, and Cu(dppb-CF3)(pz(2)Bph(2)) 3 [dppb 1,2-bis(diphenylphosphino)benzene, dppb-F = 1,2-bis[bis(3,5-difluorophenyl)phosphino]benzene, and dppb-CF3 = 1,2-bis[bis[3,5-bis(trifluoromethyl)phenyl]phosphino]benzene, pz(2)Bph(2)(-) = diphenyl-bis(pyrazol-1-yl)borate], were synthesized and investigated as luminescent guest molecules in prototype organic light-emitting diodes. Thermogravimetric analysis of 1-3 under vacuum revealed that introduction of F or CF3 substituents to the meta positions of the four peripheral phenyl groups in the dppb skeleton increased the ability of the copper(I) complexes to be sublimed. 1-3 exhibited strong green emission in amorphous films at 293 K with maximum emission wavelengths of 523-544 nm, quantum yields of 0.50-0.68, and decay times of 3.6-8.2 mu s. Molecular orbital calculations indicated that the origin of green phosphorescence from 1-3 was a mixture of sigma -> pi(star) and pi -> pi(star) transitions. Conventional bottom-emitting devices with three-layer structures containing 1-3 produced bright green luminescence with maximum external quantum efficiencies of 11.9, 16.0, and 17.7% for 1, 2 and 3, respectively.