Cyclometalated N-heterocyclic carbenes (NHC)-Ir based chromophores, Ir(C^C:)3, have attracted attention due to their promising properties as blue emitters. In this work we developed three new tris-Ir(III) carbene complexes featuring two different NHC ligands, N-phenyl,N-methyl-pyrazinoimidazol-2-yl (pmpz) and N,N-di-p-tolyl-pyrazinoimidazol-2yl (tpz) for use as blue dopants in organic light emitting diodes (OLEDs). These ligands were strategically designed to stabilize the lowest unoccupied molecular orbital (LUMO) of previously reported deep blue-emitting Ir(pmp)3 derivatives, which had shallow LUMOs and high triplet energies limiting their widescale application in OLEDs. Both meridonal and facial isomers of Ir(pmpz)3 were isolated, but due to the steric bulk of the tpz ligand, only the facial isomer of Ir(tpz)3 was formed and subsequently studied. The photophysical and electrochemical studies of all the complexes along with the previously reported deep blue-emitting fac- and mer-Ir(pmp)3 were carried out to interpret their excited state properties. The facial and meridonal isomers of the pyrazine analogs showed high photoluminescence quantum yields (PLQYs) with blue (465 nm) and green (495 nm) emission in polystyrene films, respectively. Electrochemical studies of the pyrazine analogs found a quasi-reversible oxidation wave and three reversible reduction features and their HOMO (~5.4 eV) and LUMO (~2.1 eV) levels were ideal for charge injection into the EML.OLEDs were fabricated using Ir(tpz)3 as a dopant due to its ease of synthesis and sky-blue emission. These devices obtained high electroluminescence efficiencies and high brightness.

Blue-emissive fac/mer-iridium (III) NHC carbene complexes and their application in OLEDs

ACS Spring Meeting 2021

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