Abstract
AbstractSince the first report in 2015, multiresonant thermally activated delayed fluorescent (MR‐TADF) compounds, a subclass of TADF emitters based on a heteroatom‐doped nanographene material, have come to the fore as attractive hosts as well as emitters for organic light‐emitting diodes (OLEDs). MR‐TADF compounds typically show very narrow‐band emission, high photoluminescence quantum yields, and small ΔEST values, typically around 200 meV, coupled with high chemical and thermal stabilities. These materials properties have translated into some of the best reported deep‐blue TADF OLEDs. Here, a detailed review of MR‐TADF compounds and their derivatives reported so far is presented. This review comprehensively documents all MR‐TADF compounds, with a focus on the synthesis, optoelectronic behavior, and OLED performance. In addition, computational approaches are surveyed to accurately model the excited state properties of these compounds.
Highlights
Since the first report in 2015, multiresonant thermally activated delayed and co-workers[2] (1941) in fluorescein followed by studies in other π-conjugated fluorescent (MR-thermally activated delayed fluorescence (TADF)) compounds, a subclass of TADF emitters based on a compounds such as eosin,[3] fullerene,[4]
We recently reported a much-improved computational protocol to model multiresonance TADF (MR-TADF) compounds, moving away from DFT and using instead a wave function-based approach, SCS-CC2.[49]. Excellent agreement was achieved for the ΔEST values of both DABNA-1 and 2a (Figure 4) and a proposed design of new extended derivatives offered a tantalizing path to generate molecules showing both decreasing ΔEST and increasing oscillator strength
organic light-emitting diodes (OLEDs) using purely organic D–A TADF compounds have achieved comparable, and for some colors even surpassed, performance metrics compared to state-of-the-art OLEDs employing organometallic phosphorescent complexes.[17]
Summary
Hatakeyama and co-workers[28] introduced a potential solution, coined multiresonance TADF (MR-TADF), by designing planar boron- and oxygen (or nitrogen)-containing arene compounds. The OLED with 2F-BN presented an impressive CIEy coordinate of 0.60, which is a real advance toward achieving green for MR-TADF compounds.[17] The emitters exhibited good device performances, with EQEmax (PEmax) values of 22.0 (69.8 lm W−1), 22.7 (72.3 lm W−1) and 20.9% (51.3 lm W−1) for 2F-BN, 3F-BN, and 4F-BN, respectively Due to their fused planar structure, the devices fabricated with these new emitters exhibited excimer emission. The overall yield was reported to be 27% and 14%, respectively for ADBNA-Me-Mes and ADBNA-Me-Tip. The photophysical properties of 1 wt% films of the two ABDNA derivatives were investigated using DOBNA-OAr as the host.[29b] Compare to DABNA-1 (λPL = 460 nm, 1 wt% in mCBP),[27a] these compounds showed redshifted emission of 482 and 479 nm, respectively, for ADBNA-Me-Mes and ADBNA-Me-Tip. Notably, the FWHM remained narrow (33 and 34, respectively for ADBNA-Me-Mes and ADBNA-Me-Tip). Similar to the trends in the solution-state photophysics, a 15 nm redshift in the electroluminescence spectrum was observed for the OLED with Mes3DiKTa to that of DiKTa, from CIE (0.14,0.18) to (0.12,0.32)
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