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Yellow emission is a complementary color of blue for achieving white emission. Here, we report two yellow-emitting PtAg2heterotrinuclear complexes (1and 2) of 4-ethynyl-N,N-diphenylaniline, supported by bis(diphenylphosphinomethyl)phenylphosphine (dpmp) and bis(di-o-tolylphosphinomethyl)phenylphosphine (dTolmp), respectively. The solution-processed organic light-emitting diode based on complex 1exhibits yellow emission peaked at 567 nm with the highest current efficiency (CE) of 49.7 cd A–1and an external quantum efficiency (EQE) of 14.3%. Remarkably, the device performance of complex 2containing dTolmp with a larger steric hindrance as the supporting ligand is dramatically enhanced with the CE boosting to 69.1 cd A–1and EQE of 21.7% and, more importantly, a better color saturation of yellow emission peaked at 579 nm with the CIE of (0.49, 0.50).

A hexadentate macrocyclic N-heterocyclic carbene (NHC) ligand precursor (H4L)(PF6)4containing four benzimidazolium and two secondary amine groups, has been synthesized and characterized. Coordination chemistry of this new macrocyclic diamine-tetracarbene ligand has been studied by the synthesis of its Ag(I), Au(I), Ni(II), and Pd(II) complexes. Reactions of (H4L)(PF6)4with different equiv of Ag2O result in Ag(I) complexes [Ag(H2L)](PF6)3(1) and [Ag2(H2L)](PF6)4(2). A mononuclear Au(I) complex [Au(H2L)](PF6)3(3) and a trinuclear Au(I) complex [Au3(H2L)(Cl)2](PF6) (4) are obtained by transmetalation of 1and 2with AuCl(SMe2), respectively. Reactions of (H4L)(PF6)4with Ni(OAc)2and Pd(OAc)2in the presence of NaOAc yield [Ni(L)](PF6)2(5) and [Pd(L)](PF6)2(6), respectively, containing one Ni(II) and Pd(II) ion with distorted square-planar geometry. Using more NaOAc results in the formation of unusual dinuclear complexes [Ni2(L–2H)](PF6)2(7) and [Pd2(L–2H)](PF6)2(8) (L–2H = deprotonated ligand after removing two H+ions from two secondary amine groups in L), respectively, featuring a rare M2N2core formed by two bridging amides. 7is also formed by the reaction of 5with 1.0 equiv of Ni(OAc)2·4H2O in the presence of NaOAc. Transmetalation of 2with 2.0 equiv of Ni(PPh3)2Cl2gives [Ni2(L)(μ-O)](PF6)2(9), the first example of a dinuclear Ni(II) complex with a singly bridging oxo group. 9is converted to 7in good yield through the treatment with NaOAc.