Essential Role of Ancillary Ligand in Color Tuning and Quantum Efficiency of Ir(III) Complexes with N-Heterocyclic or Mesoionic Carbene Ligand: A Comparative Quantum Chemical Study.

Tuning photoluminescence properties is of prime importance for designing efficient light emitting diode (LED) materials. Here, we perform a computational study on the effect of normal N-heterocyclic carbene (NHC) and abnormal mesoionic carbene (MIC) ligands on the photoluminescence properties of some Ir(III) complexes, which are very promising LED materials. We find MIC as the privileged ligand in designing triplet emitters. The strong σ-donating and moderate π-accepting properties of MIC render a lower access to the nonemissive triplet metal-centered state (3MC), resulting in lowering the nonradiative rate constant ( knr) and correspondingly achieving higher quantum efficiency. We also demonstrate that the judicial choice of ancillary ligand can improve the efficiency of these materials even further. This quantum chemical investigation focuses on the importance of MIC as cyclometalating ligand and the substantial effects of ancillary ligands in controlling the color tuning and quantum efficiency for optoelectronic applications.