Tripyridylbenzene-based blue dendrimer emitters for efficient solution-processable single-emissive-layer hybrid white organic light-emitting diodes
A series of light-emitting dendrimers T42Bn, T24Bn, T26Bn and T35Bn based on electron-donating units of the second-generation butyicarbazoles (G2Cz) as dendrons and electron-withdrawing core of tripyridylbenzene (TPB) were designed and synthesized. The desirable blue luminogens were obtained due to the rational molecular design based on the twisted skeleton of all the molecules despite the donors of G2Cz moieties connected to the central acceptors of TPB via a para-phenylene bridge. Their thermal, photophysical, density functional theory calculation and electrochemical properties were fully investigated. Thanks to the excellent thermal stability, film-forming ability as well as the favourable energy levels of the dendrimers, efficient solution-processed hybrid white organic light-emitting diodes (WOLEDs) were achieved by employing these blue dendrimers and the orange emitter of (acetylacetonato)-bis[2-(thieno [3,2-c]pyridin-4-yl)phenyl]iridium(III) (PO-01) as an emitting layer (EML). Among them, the device based on T42Bn exhibited the highest maximum current efficiency (CE max ) of 10.25 cd/A with a maximum external quantum efficiency (EQE max ) of 3.94% and Commission International de I'Eclairage (CIE) coordinates of (0.34, 0.39), benefiting from the largest ƞ PLQY and the highest electron transport capability of T42Bn and thus the enhancement of charge carrier balance in the device. In addition, the CIE coordinates of all the single-emitting-layer fluorescence/phosphorescence hybrid devices are very close to the benchmark white region of (0.33, 0.33). Our findings demonstrate the potential candidates of the solution-processable blue dendronized emitters for applications in full-color flat-panel displays and white lighting.
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