The isomeric effect of thienopyridazine-based iridium complexes

Abstract

Three tris-cyclometalated iridium(III) complexes based on different thienopyridazine isomeric ligands were successfully synthesized. The influence of isomerism on material properties was comprehensively evaluated. The thieno[2,3-d]pyridazine based isomeric complexes IrM and IrP have similar photophysical properties. However, sulfur atoms regulate intramolecular hydrogen bonding in complex IrM, leading to differences in other properties. Complex IrM exhibits ambipolar transport properties, good solubility and excellent stability (T_d = 425 °C), while IrP shows electronic transport properties, bad solubility and moderate stability (T_d = 374 °C). The thieno[3,4-d]pyridazine based complex IrC has very low stability (T_d = 214 °C) and significantly reduced optical energy gap compared to other isomers, making it almost non-luminescent. Complexes IrM and IrP are excellent yellow phosphorescent dopants for OLED application, and the maximum power efficiency (PE) and external quantum efficiency (EQE) based on them were 76.0 lm W⁻¹, 26.7% and 73.5 lm W⁻¹, 28.3%, respectively. This indicates that thieno[2,3-d]pyridazine based complexes have great potential for application in full-color displays and solid-state lighting.