Dinuclear Ir(III) complex based on different flanking and bridging cyclometalated ligands: An impressive molecular framework for developing high performance phosphorescent emitters

Dinuclear Ir(III) complexes are drawing increasing attentions due to their impressive luminescent properties. In this work, we report a promising molecular framework for developing novel charge-neutral dinuclear Ir(III) complexes. Unlike most of dinuclear Ir(III) complexes reported previously, the two Ir centers are held by a cyclometalated bridging ligand which can form a rigid structure to suppress the nonradiative decay. The resultant dinuclear Ir(III) complexes are highly emissive in both solution and doped film with photoluminescent quantum yields up to 0.78. Two functional flanking ligands are used to further tune the luminescent properties. Compared with that of corresponding conventional mononuclear Ir(III) complex, the emission of dinuclear Ir(III) complexes can be greatly red-shifted by over 110 nm. Theoretical calculations are performed to understand these impressive photophysical properties of these dinuclear Ir(III) complexes. Finally, solution-processed organic light-emitting diodes (OLEDs) are fabricated to evaluate their electroluminescent properties. The orange-red device based on BuPyPm1 exhibits outstanding performance with the external quantum efficiency of 23.9%, which is the highest value ever reported for solution-processed OLEDs based on dinuclear Ir(III) complexes. This work demonstrates the great potential of the proposed molecular framework in developing phosphorescent emitters for highly efficient OLEDs.