Rational design and characterization of efficient deep-red iridium(III) complexes with 2-(benzothienyl)pyridine and tetraphenylimidodiphosphinate ligands

Herein, a new series of deep-red phosphorescent cyclometalated iridium(III) complexes (Ir-1 similar to Ir-3) with 2-(benzothienyl)pyridine derivatives (R-btp) as cyclometalated ligands and tetraphenylimidodiphosphinate (tpip) as ancillary ligands were synthesized and fully characterized. The crystal structures of three complexes were determined by X-ray analysis, displaying multiple pi & mldr; pi and C-H & mldr; pi interactions. Their structures and photophysical properties were systematically investigated with experimental and theoretical methods. The results reveal complex Ir-3 functionalized with the CF3 groups exhibits a remarkable red-shifted and a higher quantum yield compared to fluorinated complexes Ir-1 and Ir-2. As expected, the deep-red organic light-emitting diodes (OLEDs) device D-3 using Ir-3 as the emitting layer achieves the best electroluminescent performance with a promising maximum external quantum efficiency (EQE(max)) of 11.3 %, accompanied by CIE coordinates of (0.67, 0.33) and narrow full width at half maximum (FWHM) of 41 nm. It is anticipated that this research could provide a rational design strategy for pure deep-red-emitting phosphorescent iridium complexes in the fabrication of high-efficiency OLEDs.