An oxygen-bridged triarylamine polycyclic unit based tris-cyclometalated heteroleptic iridium(iii) complex: correlation between the structure and photophysical properties

Abstract

A novel oxygen-bridged triarylamine polycyclic unit based tris-cyclometalated heteroleptic iridium(III) complex (Ir–NO) has been designed and prepared. Similar iridium(III) complexes (Ir–N and Ir–O) have also been prepared for comparison. The single crystal structure indicates that the oxygen-bridged triarylamine polycyclic unit of Ir–NO shows certain planarity, resulting in obvious rigidity and interesting π–π stacking. Additionally, Ir–NO shows a larger redshift emission (586 nm) and a longer emission lifetime (628 ns) than Ir–N (525 nm, 344 ns) and Ir–O (543 nm, 436 ns), and the phosphorescence color can be tuned from green to orange. Electrochemical experiments and DFT calculations reveal that Ir–NO exhibits a high HOMO energy level and intraligand charge transfer (³ILCT) excited state properties, which is in contrast to the low HOMO energy level and metal-to-ligand charge transfer (³MLCT) excited state properties in Ir–N and Ir–O. This result can be attributed to the strong electron-donating ability of the unit.