The 1,3,5-triazine electron-acceptor has become one of the most popular building blocks for the design of thermally activated delayed fluorescence (TADF) materials. Many TADF design strategies are first applied in compounds that contain triazines, and there are numerous examples of OLEDs with triazine-containing emitters that show high efficiencies and long operating lifetimes. We provide a comprehensive review of triazine-containing TADF emitters. This review is organized according to the triazine-derived structural motifs, such as number and position of electron-donor groups in donor-acceptor type emitters, the -bridging linkers employed, and the design of through-space charge-transfer (TSCT) emitter. We correlate the structure of the compounds with their optoelectronic properties and the corresponding performance of the organic light-emitting diode devices.
We show how borylation of an acceptor-donor-acceptor (A-D-A) thermally activated delayed fluorescence (TADF) emitter, DIDOBNA-N, transforms the compound into a multi-resonant TADF (MR-TADF) emitter, MesB-DIDOBNA-N. DIDOBNA-N emits bright blue light (𝜆PL = 444 nm, FWHM = 64 nm, 𝛷PL = 81%, 𝜏d = 23 𝜇s, 1.5 wt% in TSPO1). The deep blue organic light-emitting diode (OLED) based on this compound shows a very high maximum external quantum efficiency (EQEmax) of 15.3% for a device with CIEy of 0.073. The MR-TADF emitter, MesB-DIDOBNA-N shows efficient and narrowband violet emission (𝜆PL = 402 nm, FWHM = 19 nm, 𝛷PL = 74.7%, 𝜏d = 133 𝜇s, 1.5 wt% in TSPO1). The OLED with MesB-DIDOBNA-N shows out-standing efficiency for a violet OLED at 9.3% and CIEy = 0.044, which is the bluest EL reported for a MR-TADF OLED to date. Noteworthy are the CIE coordinates of (0.166, 0.045), which are very close to the Rec.2020 standard for blue (0.131, 0.046). The EQEmax values were improved from 9.3% to 13.6% by increasing the concentration of the emitter in the host from 1.5 wt% to 5 wt%.
Corannulene-derived materials have been extensively explored in energy storage and solar cells, but, however, are rarely documented as emitters in light-emitting sensors and organic light-emitting diodes (OLEDs), due to low exciton utilization. Here, we report a family of multi-donor and acceptor (multi-D-A) motifs, TCzPhCor, TDMACPhCor, and TPXZPhCor, using corannulene as the acceptor and carbazole (Cz), 9,10-dihydro-9,10-dimethylacridine (DMAC), and phenoxazine (PXZ) as the donor, respectively. By decorating corannulene with different donors, multiple phosphorescence is realized. Theoretical and photophysical investigations reveal that TCzPhCor shows room-temperature phosphorescence (RTP) from the lowest-lying T1; however, for TDMACPhCor, dual RTP originating from a higher-lying T1 (T1H) and a lower-lying T1 (T1L) can be observed, while for TPXZPhCor, T1H-dominated RTP occurs resulting from a stabilized high-energy T1 geometry. Benefiting from the high-temperature sensitivity of TPXZPhCor, high color-resolution temperature sensing is achieved. Besides, due to degenerate S1 and T1H states of TPXZPhCor, the first corannulene-based solution-processed afterglow organic light-emitting diodes (OLEDs) is investigated. The afterglow OLED with TPXZPhCor shows a maximum external quantum efficiency (EQEmax) and a luminance (Lmax) of 3.3% and 5167 cd m-2, respectively, which is one of the most efficient afterglow RTP OLEDs reported to date.
Since the seminal report by Adachi and co-workers in 2012, there has been a veritable explosion of interest in the design of thermally activated delayed fluorescence (TADF) compounds, particularly as emitters for organic light-emitting diodes (OLEDs). With rapid advancements and innovation in materials design, the efficiencies of TADF OLEDs for each of the primary color points as well as for white devices now rival those of state-of-the-art phosphorescent emitters. Beyond electroluminescent devices, TADF compounds have also found increasing utility and applications in numerous related fields, from photocatalysis, to sensing, to imaging and beyond. Following from our previous review in 2017 (
Carbene coinage metal carbazolates are currently the most efficient organometallic TADF emitters. Herein we report on the photophysical influence of introducing a [2.2]paracyclophane moiety via a carbazolophane ligand instead of carbazolate, which greatly enhances the radiative rate constants by a factor of three to 1-3·106 s-1 for triplet exciton emission.
Nitrogen-containing polycyclic aromatic hydrocarbons (N-PAH) have been widely used as deep lowest unoccupied molecular orbital (LUMO) acceptors in donor-acceptor (D-A) red thermally activated delayed fluorescent (TADF) emitters and their use in organic light-emitting diodes. However, most of the studies have focused disparately on donor/acceptor combinations to yield efficient emitters, while it is rare that there is a methodological study to investigate the influence of the nitrogen (N) doping ratios on the ground and excited states of PAH acceptors. Here, we report a family of four different N-PAH acceptors containing different numbers of nitrogen atoms within the N-PAH and their use in D-A TADF emitters, DMACBP, DMACPyBP, DMACBPN and DMACPyBPN, when coupled to the same donor, 9,9-dimethyl-9,10-dihydroacridine (DMAC). As the nitrogen content in the acceptor increases the LUMO becomes progressively more stabilized while the singlet-triplet energy gap (ΔEST) decreases and the rate constant for reverse intersystem crossing (kRISC) increases. In particular, introducing nitrogen at the 10-position of the dibenzo[a,c]phenazine (BP) leads to a more than ten-fold enhancement in kRISC in DMACPyBP and DMACPyBPN compared to DMACBP and DMACBPN. Among the OLEDs with all four emitters that with DMACBPN demonstrates the highest EQEmax of 19.4% at an emission peak of 588 nm. while the deepest red emitting device employed DMACPyBPN (EL = 640 nm) with an EQEmax of 5.4%.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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