Unsymmetrical substituted steric terfluorenes for solution-processed narrowband deep-blue organic light-emitting diodes with CIEy = 0.06

Abstract

Multiple-site functionalization of deep-blue light-emitting conjugated molecules can not only optimize photo-electrical processing to obtain robust electroluminescent behavior but also enhance the film-forming ability to manufacture large-area film via solution processing technology. Herein, we demonstrate a pendant side-functionalization to prepare a series of unsymmetrical substituted steric terfluorenes (MC8 and MC6Cz) via originally introducing the alkoxy and carbazole group at the 4-position of fluorene segments for the narrowband ultra-deep-blue solution-processed organic light-emitting diodes (OLEDs). Both materials exhibited an ultra-deep-blue emission with CIE coordinates of (0.16, 0.06) and PLQY efficiencies of ∼60% due to the single-molecular exciton behavior without polariton formation, confirmed by the time-resolved transient spectroscopy. Interestingly, compared to the MC8, MC6Cz films present stable deep-blue emission without obvious green-band emission when thermally annealed in the air or irradiated for 3 hours under UV light, attributed to the self-encapsulation of the pendant carbazole group. Finally, MC6Cz-based OLEDs exhibited a narrowband ultra-deep-blue emission, a high brightness at low current density, with a high external quantum efficiency (EQE) of 1.17% and CIE coordinates of (0.16, 0.06). All the above results confirm that the introduction of the Cz group inhibits the aggregation between molecular main chains, realizing the single molecular mechanism of exciton behavior, establishing the two-dimensional carrier transport channel, and improving the morphology, spectral stability and efficiency of the material, which are conducive to the realization of efficient and stable solution-processed deep-blue light-emitting devices.