Pyrazolate-Bridged NHC Cyclometalated [Pt 2 ] Complexes and [Pt 2 Ag(PPh 3 )] + Clusters in Electroluminescent Devices.

The ionic transition metal complexes (iTMCs) [{Pt(C ∧ C*)(μ-Rpz)} 2 Ag(PPh 3 )]X (HC ∧ C* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1 H -imidazole-2-ylidene, X = ClO 4 /PF 6; Rpz = pz 1 a /2a , 4-Mepz 1 b /2b , and 3,5-dppz 1 c /2c ) were prepared from the neutral [{Pt(C ∧ C*)(μ-Rpz)} 2 ] (Rpz = pz A , 4-Mepz B , and 3,5-dppz C ) and fully characterized. The "Ag(PPh 3 )" fragment is in between the two square-planar platinum units in an "open book" disposition and bonded through two Pt-Ag donor-acceptor bonds, as shown by X-ray diffraction (d Pt-Ag ∼ 2.78 Å, 1a - 1c ). 195 Pt{ 1 H} and 31 P{ 1 H} NMR confirmed that these solid-state structures remain in solution. Photoluminescence studies and theoretical calculations on 1a , were performed. The diphenylpyrazolate derivatives show the highest photoluminescence quantum yield (PLQY) in the solid state. Therefore, 2c and its neutral precursor C were selected as active materials on light-emitting devices. OLEDs fabricated with C showed a turn-on voltage of 3.2 V, a luminance peak of 21,357 cd m -2 at 13 V, and a peak current efficiency of 28.8 cd A -1 (9.5% EQE). They showed a lifetime t 50 of 15.7 h. OLEDs using 2c showed a maximum luminance of 114 cd m -2 , while LECs exhibited a maximum luminance of 20 cd m -2 and a current efficiency of around 0.2 cd A -1 , with a t 50 value of 50 min.