Unlocking the Potential of Pyrimidine Conjugate Emitters to Realize High‐Performance Organic Light‐Emitting Devices

Abstract

1 of 5) 1600675 emitter combined with sophisticated device engineering, including an appropriate choice of neighboring materials, is absolutely imperative to achieve high η p OLEDs realizing both high η ext and low drive voltages at high brightness over 1000 cd m −2 . While we developed novel pyrimidine conjugated emitters and the devices, Yang's group reported a pyrimidinebased green TADF emitters realizing a high η ext,max close to 25% and an η p of 74 lm W −1 . [16] However, we note that this device showed a high drive voltage of 3.4 V at 1 cd m −2 and a large efficiency roll-off with η p,1000 of 37 lm W −1 at a high brightness of 1000 cd m −2 .Herein, we investigated the structure-property relationships among pyrimidine conjugate emitters revealing an effective molecular design for high-performance OLEDs. Consequently, we successfully developed a highly luminescent pyrimidine conjugate emitter named PXZ-PPM exhibiting a high η ext of over 25%, with low driving voltages at Commission Internationale de l'Eclairage chromaticity coordinates (CIE) of (0.36, 0.58), and exceptionally low efficiency roll-off realizing η ext of over 22% at a high brightness of 1000 cd m −2 . These OLEDs also exhibited an η p of over 110 lm W −1 (84.9 cd A −1 , η ext = 25.1%) while maintaining extremely low voltages of 2.2 V at 1 cd m −2 and 3.0 V at 1000 cd m −2 , and an η p,1000 of 78.3 lm W -1 (75.5 cd A -1 , η ext = 22.3%). These performances clearly exceed those of previous TADF devices and are comparable to those of their stateof-the-art phosphorescent counterparts. [17][18][19][20][21][22][23] So far, our TADF molecules, denoted as Ac-RPM (R = H, CH 3 , and phenyl), were synthesized introducing two 9,10-dihydro-9,9-dimethyl-10-phenylacridine moieties at the 4-and 6-positions with regard to the pyrimidine unit and exhibited high photoluminescent quantum yields (η PL s) of approximately 80% and strong TADF properties. However, all Ac-RPM derivatives showed similar emission peaks (λ em ) around 490 nm and ΔE ST of 0.19 eV. Thus, the structure-property relationships should be clearly identified for effective molecular design and superior OLED performances based on pyrimidine conjugate emitters. With this aim, we designed two novel pyrimidinebased emitters named PXZ-PPM and Ac-NPM (Figure 1). Ac-NPM possessed a piperidine moiety at the 2-position of pyrimidine. In this sense, stronger electron-donating properties are expected to increase the lowest unoccupied molecular orbital (LUMO) levels, thereby leading to wider energy gaps (E g ) as compared to the phenyl-based Ac-PPM emitter. On the other hand, PXZ-PPM possessed phenoxazine (PXZ) moieties

Photoluminescence Properties of Aryl‐, Arylvinyl‐, and Arylethynylpyrimidine Derivatives

“…Compounds 80–88 are characterized by delayed emission lifetimes (τ d ) of 2–330 μs with high fluorescence quantum yield in doped thin films (up to 0.92 for 88 ), two key parameters for OLED based on thermally activated delayed fluorescence (TADF) emitters –…”

Achieving Submicrosecond Thermally Activated Delayed Fluorescence Lifetime and Highly Efficient Electroluminescence by Fine-Tuning of the Phenoxazine–Pyrimidine Structure

“… 24 The later modification of a promising phenoxazine–pyrimidine structure by different aryl and methyl moieties at the pyrimidine unit resulted in subsequent lowering of the TADF decay time down to 1.99 μs while preserving a high emission yield. 24 , 25 Further substantial shortening of the TADF lifetime down to 1.32 μs for the analogous phenoxazine–pyrimidine compounds was achieved by introducing Cl or Br atoms and enhancing both ISC and rISC rates due to internal heavy-atom effect, simultaneously preserving a high fluorescence quantum yield. This strategy also allowed to increase peak EQE values up to 25.3%.…”

Molecular Orientations of Delayed Fluorescent Emitters in a Series of Carbazole-Based Host Materials

“…We selected three types of pyrimidine-based TADF emitters named Ac26DPPM (Nakao et al, 2017), AcPPM (Komatsu et al, 2016a), and PXZPPM (Komatsu et al, 2016b) with different donor group(s) such as dimethylacridine (Ac) and phenoxiazine (PXZ) (Figure 1 and Table 2). By comparing these three molecules, we can obtain insight into the effects of two factors: (i) donor number, which reflects the molecular shape anisotropy in these comparisons, and (ii) donor structure.…”