A benzoindole-cored building block for deep blue fluorescent materials: Synthesis, photophysical properties, and applications in organic light-emitting diodes

Deep blue fluorescent materials are crucial in the commercialization of organic light-emitting diodes (OLEDs) for full-color displays or solid-state lighting sources. In this work, a series of aromatic ring compounds, based on a newly designed 2-(pyridine-4-yl)-3-phenyl-1H-benzo[g]indole core, have been synthesized, on which donor (D) and acceptor (A) groups are bonded in a Ψ-type configuration, forming a D-π-A-π-D structure. The electronic structure and photophysical properties have been explored, as well as the applications in the blue OLEDs. The results show that multistate couplings exist between the three D-π-A-π-D moieties, resulting in a high photoluminescence quantum yield up to 76.01% peaking at around 410 nm, and a depressed efficiency roll-off at high luminance. The deep blue OLEDs based on CzCNBPyIp emitter exhibits stable emission peaking at 416 nm with a negligible efficiency roll-off at a high luminance range of 1 000-10 000 cd m-2, and corresponding CIEx,y = (0.162, 0.085) and maximum EQE = 2.6%, making it one of the highest performing solution-processed deep blue fluorescent devices. This work provides an alternative method for the deep blue fluorescent material design toward solution processing OLEDs.