From Mononuclear to Dinuclear Iridium(III) Complex: Effective Tuning of the Optoelectronic Characteristics for Organic Light-Emitting Diodes

Phosphorescent dinuclear iridium­(III)
complexes that can show high luminescent efficiencies and good electroluminescent
abilities are very rare. In this paper, highly phosphorescent 2-phenylpyrimidine-based
dinuclear iridium­(III) complexes have been synthesized and fully characterized.
Significant differences of the photophysical and electrochemical properties
between the mono- and dinuclear complexes are observed. The theoretical
calculation results show that the dinuclear complexes adopt a unique
molecular orbital spatial distribution pattern, which plays the key
role of determining their photophysical and electrochemical properties.
More importantly, the solution-processed organic light-emitting diode
(OLED) based on the new dinuclear iridium­(III) complex achieves a
peak external quantum efficiency (ηext) of 14.4%,
which is the highest ηext for OLEDs using dinuclear
iridium­(III) complexes as emitters. Besides, the efficiencies of the
OLED based on the dinuclear iridium­(III) complex are much higher that
those of the OLED based on the corresponding mononuclear iridium­(III)
complex.