Dicyano‐Imidazole: A Facile Generation of Pure Blue TADF Materials for OLEDs

Abstract

A series of dicyano-imidazole-based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain pure blue-emitting organic lightemitting diodes (OLEDs). The targeted molecules used dicyano-imidazole with a short-conjugated system as the electron acceptor to strong intermolecular π-π interactions, and provide a relatively shallow energy level of the lowest unoccupied molecular orbital (LUMO). The cyano group was selected to improve imidazole as an electron acceptor due to its prominent electron-transporting characteristics. Four different electron donors, that is, 9,9-dimethyl-9,10-dihydroacridine (DMAC), 10H-spiro(acridine-9,9'-fluoren) (SPAC), and 9,9diphenyl-9,10-dihydroacridine (DPAC), were used to alternate the highest occupied molecular orbital (HOMO) energy level to tune the emission color further. The crowded molecular structure in space makes the electron donor and acceptor almost orthogonal, reducing the energy gap (ΔE ST ) between the first excited singlet (S 1 ) and the triplet (T 1 ) states and introducing significant TADF property. The efficiencies of the blue-emissive devices with imM-SPAC and imM-DMAC obtained in this work are the highest among the reported imidazole-based TADF-OLEDs, which are 13.8 % and 13.4 %, respectively. Both of Commission Internationale de l'Eclairage (CIE) coordinates are close to the saturated blue region at (0.17, 0.18) and (0.16, 0.19), respectively. Combining these tailor-made TADF compounds with specific device architectures, electroluminescent (EL) emission from sky-blue to deep-blue could be achieved, proving their great potential in EL applications.

Thiazoline Carbene–Cu(I)–Amide complexes: Efficient White Electroluminescence from Combined Monomer and Excimer Emission

“…47 Furthermore, the hole-transporting 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) were combined to form a stepwise hole-transport layer (HTL), aiming to promote a smooth hole injection from the HTL into the emitting layer (EML). 48 On the other hand, 1,3,5-tris[(3-pyridyl)-phen-3-yl]benzene (TmPyPB) was used as the electron transport layer (ETL), 49 due to its excellent carrier transport capability of 1 × 10 −3 cm 2 / (V s) and a wide triplet energy gap (E T ) of 2.78 eV. The device with mCBP outperformed those with the other host materials.…”

Imidazole Acceptor for Both Vacuum-Processable and Solution-Processable Efficient Blue Thermally Activated Delayed Fluorescence

“… 13 Lu and co-workers reported dicyanoimidazole-based emitters named imM-SPAC and imM-DMAC that showed blue emissions with CIE coordinates of (0.17, 0.18) and (0.16, 0.19), respectively. 14 …”

“…13 Lu and co-workers reported dicyanoimidazole-based emitters named imM-SPAC and imM-DMAC that showed blue emissions with CIE coordinates of (0.17, 0.18) and (0.16, 0.19), respectively. 14 Considering the high LUMO energy level and high T 1 energy of the imidazole core, we can expect efficient deep-or pure-blue TADF materials by appropriate molecular modification. In this work, we investigate four donor−acceptor-type emitters (Figure 1) using BI-derivatives as acceptors in combination with 9,10-dihydro-9,9-dimethylacridine (Ac) electron-donating derivatives.…”

“…Thus, imidazole is one of the good candidates for the molecular fragments of TADF materials. So far, five reports have been found for TADF emitters that possess an imidazole core in their application to OLEDs. − Wang and co-workers reported two phenanthroimidazole-based green TADF emitters, named PPZTPI and PPZPPI . For benzimidazole (BI)-based TADF emitters, Adachi and co-workers reported a green emitter named DHPZ-2BI, and Zysman-Colman and co-workers also reported four green emitters .…”

“…Kido and co-workers reported a series of BI-based emitters and one of which was named PXZ-BIP exhibited sky-blue emission in Commission Internationale de l′Eclairage (CIE) coordinates ( x , y ) of (0.22, 0.42) . Lu and co-workers reported dicyanoimidazole-based emitters named imM-SPAC and imM-DMAC that showed blue emissions with CIE coordinates of (0.17, 0.18) and (0.16, 0.19), respectively …”