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Dicyano‐Imidazole: A Facile Generation of Pure Blue TADF Materials for OLEDs
Author(s) -
Yi RongHuei,
Liu GuanYang,
Luo YanTeng,
Wang WeiYu,
Tsai HanYu,
Lin ChienHsiang,
Shen HsiangLing,
Chang ChihHao,
Lu ChinWei
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202101807
Subject(s) - homo/lumo , imidazole , oled , electroluminescence , acceptor , excited state , photochemistry , electron acceptor , materials science , molecule , singlet state , band gap , chemistry , optoelectronics , stereochemistry , nanotechnology , physics , organic chemistry , atomic physics , layer (electronics) , condensed matter physics
A series of dicyano‐imidazole‐based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain pure blue‐emitting organic light‐emitting 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), 10 H ‐spiro(acridine‐9,9’‐fluoren) (SPAC), and 9,9‐diphenyl‐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 (Δ E 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.