Synthesis of heteroleptic iridium complexes with sterically hindered methyl groups on pyrazole ligands for efficient yellow and green light-emitting electrochemical cells

• Iridium complexes (1a–2b) were synthesized using pyrazole based ancillary ligands.
• DFT and TDDFT calculations were performed for all complexes.
• Light-emitting electrochemical cells (LECs) were fabricated and characterized.
• LECs based on these complexes resulted in yellow and green electroluminescence.

We report the synthesis of four cationic iridium complexes, [Ir(ppy)2(mepzpy)]PF6 (1a), [Ir(dfppy)2(mepzpy)]PF6 (1b), [Ir(ppy)2(dmpzpy)]PF6 (2a), and [Ir(dfppy)2(dmpzpy)]PF6 (2b), containing the methyl-substituted pyrazole-based ancillary ligand and the phenylpyridine-based cyclometalating ligands. UV–visible, photoluminescence (PL), and voltammetric measurements were made to study the photophysical and electrochemical properties of complexes 1a–2b. Light-emitting electrochemical cells (LECs) were fabricated, which showed yellow emission for complexes 1a and 2a and green emission for complexes 1b and 2b. The LEC incorporating 2b exhibited a high luminance of 658 cd m−2 and a current efficiency of 0.34 cd A−1. The higher luminance and efficiency of the device based on 2b were due to the smooth surface morphology and the presence of sterically hindered dimethyl groups on the ancillary ligand (dmpzpy), which causes a more balanced charge carrier injection and recombination.

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