Quantum chemical investigation on the Ir(iii) complexes with an isomeric triazine-based imidazolium carbene ligand for efficient blue OLEDs‡

We investigate, for the first time, a number of iridium(III) complexes formed with an isomeric triazine based imidazolium carbene (imi-trzn) ligand and their corresponding photophysical properties for efficient blue organic light emitting diodes (OLEDs). In this process, we choose phenylpyridine or bipyridine as an ancillary ligand and vary the positions of the nitrogens in the other cyclometalated ligands, imi-trzn. Density functional theory (DFT) and time-dependent DFT have been employed to elucidate the effect of different isomers of the imi-trzn ligand on the emission color tuning and quantum efficiency. The different isomers of the cyclometalating ligand chelate with Ir(III) through different coordinating sites and form cationic and neutral complexes. The results demonstrate that the complexes formed with an N-coordinating site of the ligand are more stable compared to the complexes formed through a C-coordinating site. However, the quantum efficiency shows a reverse trend. We further find that 3ILCT transition character along with some 3MLCT is required for the design of efficient phosphors with higher radiative and lower non-radiative decay rates. These results might be helpful for the design of novel and more efficient blue emitters for OLED applications using strategic modification of ligands.