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

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.