Unconventional Three-Armed Luminogens Exhibiting Both Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence Resulting in High-Performing Solution-Processed Organic Light-Emitting Diodes

Abstract

In this work, three-armed luminogens IAcTr-out and IAcTr-in were synthesized and used as emitters bearing triazine and indenoacridine moieties in thermally activated delayed fluorescence organic light-emitting diodes (OLEDs). These molecules could form a uniform thin film via the solution process and also allowed the subsequent deposition of an electron transporting layer either by vacuum deposition or by an all-solution coating method. Intriguingly, the new luminogens displayed aggregation-induced emission (AIE), which is a unique photophysical phenomenon. As a nondoped emitting layer (EML), IAcTr-in showed external quantum efficiencies (EQEs) of 11.8% for the hybrid-solution processed OLED and 10.9% for the all-solution processed OLED with a low efficiency roll-off. This was evident by the higher photoluminescence quantum yield and higher rate constant of reverse intersystem crossing of IAcTr-in, as compared to IAcTr-out. These AIE luminogens were used as dopants and mixed with the well-known host material 1,3-bis( N-carbazolyl)benzene (mCP) to produce a high-efficiency OLED with a two-component EML. The maximum EQE of 17.5% was obtained when using EML with IAcTr-out doping (25 wt %) into mCP, and the OLED with EML bearing IAcTr-in and mCP showed a higher maximum EQE of 18.4% as in the case of the nondoped EML-based device.

Effective Design Strategy for Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence Emitters Achieving 18% External Quantum Efficiency Pure-Blue OLEDs with Extremely Low Roll-Off

“…At this stage, most of the highly polar solvents are excluded from the aggregate, thus leading to the emitters becoming more nonpolar in the aggregate accompanied by weakened ICT behavior. 38 Another factor to consider is that the blue-shift emission caused by the reduction of Stokes shift may be derived from the suppressed geometric relaxation. 39 Therefore, both emitters exhibited enhanced intensity and blue-shifted PL spectra peaks in the aggregation state.…”

Multichromophore Molecular Design for Efficient Thermally Activated Delayed Fluorescence Emitters with Near-Unity Photoluminescence Quantum Yields

“…33 Choi et al reported a treble core TADF emitter IAcTr-out wherein diphenyltriazine acceptors were linked to three indenoacridine donors that are attached around a central benzene ring. 34 The IAcTr-out possessed a small DEST of 0.05 eV and FPL of 48% in 25 wt% doped mCP film. The TADF emitter exhibited aggregation-induced emission (AIE) and the solution-processed OLED showed an EQEmax of 17.5% with CIE of (0.29, 0.54).…”

“…The TADF emitter exhibited aggregation-induced emission (AIE) and the solution-processed OLED showed an EQEmax of 17.5% with CIE of (0.29, 0.54). 34 These examples demonstrate that the multiple emitting cores design is an effective approach to improve molecular photophysics and electroluminescence properties. [30][31][32][33][34] In this work, we connect 4,5-di(9H-carbazol-9-yl) phthalonitrile (2CzPN) to a central benzene ring to construct dual and treble core TADF emitters and these emitters achieved both high FPL and small DEST.…”

Aggregation‐Induced Delayed Fluorescence

“…Recently, in addition to typical AIDF materials containing an electron‐withdrawing BP core as discussed above, more and more AIDF materials with quite different molecular structures had been reported, such as derivatives from diphenylsulfone, dibenzothiophene‐S,S‐dioxide, quinoxaline, xanthone, phenothiazine‐5,5‐dioxide, anthraquinone, triazine, and so forth (Figure ) . These materials also showed advances in constructing nondoped OLEDs with suppressed efficiency roll‐off, which had been described in recent literatures .…”