Multifunctional homoleptic iridium(III) dendrimers towards solution-processed nondoped electrophosphorescence with low efficiency roll-off

A series of new iridium dendrimers comprised of bifunctional charge transport peripheral groups have been designed and facilely synthesized. The relationship between the structures and their photophysical, electrochemical and electrophosphorescent performances is investigated. Through the incorporation of rigid electron-transporting phosphine oxide groups and/or hole-transporting arylamine units, the new complexes all have good thermal stabilities with high glass-transition temperature up to 284°C. Besides, the peripheries sufficiently shield the emissive core from the intermolecular interactions and prevent luminance quenching in neat films. Solution-processed phosphorescent organic light-emitting device (PhOLED) based on bipolar phosphor 2 as neat emitter achieves a maximum current efficiency of 12.4cdA−1 with Commission Internationale de l’Eclairage coordinates of (0.57, 0.42), and the value remains at 11.5cdA−1 at a practical luminance of 1000cdm−2. This low roll-off can be attributed to the bipolar nature of the emitter. This indicates that rational incorporation of charge-transporting moieties into the sphere of iridium(III) core is a simple and effective approach to develop efficient host-free phosphors for solution-processable nondoped PhOLEDs.