Isomeric N‐Linked Benzoimidazole Containing New Electron Acceptors for Exciplex Forming Hosts in Highly Efficient Blue Phosphorescent OLEDs. Issue 13 (23rd May 2017)

• Record Type: Journal Article
• Authors: Hu, Jia; Zhao, Chenyang; Zhang, Tianmu; Zhang, Xianping; Cao, Xudong; Wu, Qingjing; Chen, Yonghua; Zhang, Di; Tao, Youtian; Huang, Wei
• Is Part Of: Advanced optical materials. Volume 5:Issue 13(2017:Jul.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-05-23
• Subjects: blue phosphorescence -- electron acceptors -- electron transport -- exciplexes -- organic light‐emitting diodes; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.201700036
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract : Three benzoimidazole containing new electron‐accepting materials of 1, 3, 5‐tris(2‐(pyridin‐2‐yl)‐1 H ‐benzo[ d ]imidazol‐1‐yl)benzene ( i TPyBIB), 1, 1′, 1′′‐(pyridine‐2, 4, 6‐triyl)tris(2‐phenyl‐1 H ‐benzo[ d ]imidazole) ( i TPBIPy), and 1, 1′, 1′′‐(pyridine‐2, 4, 6‐triyl)tris(2‐(pyridin‐2‐yl)‐1 H ‐benzo[ d ]imidazole) ( i TPyBIPy) are designed and synthesized. Compared to the commercial electron‐transport 2, 2, 2‐(1, 3, 5‐phenylene)‐tris(1‐phenyl‐1 H ‐benzimidazole) (TPBI) with the C‐atom in benzoimidazole linked to the central phenyl ring, the introduction of isomeric N‐linkage to the central phenyl or pyridine ring in three compounds remarkably simplifies the synthesis to a one‐step CN coupling reaction. i TPyBIB, i TPBIPy, and i TPyBIPy exhibit comparable highest occupied molecular orbital (≈6.0 eV) and lowest unoccupied molecular orbital (≈2.5 eV) energy levels, similar triplet energy levels of ≈2.65 eV with TPBI, whereas reduced electron‐transport properties. All materials can be applied as electron acceptors to form universal exciplex with general hole‐transport electron donors, such as N, N ′‐dicarbazolyl‐3, 5‐benzene ( m CP), 4, 4′, 4′′‐tris( N ‐carbazolyl)‐triphenylamine (TCTA), and 1, 1‐bis[4‐[ N, N ‐di( p ‐tolyl)‐amino]phenyl]cyclohexane (TAPC) in the blended films with 1:1 molar ratio. A maximum external quantum efficiency of 17.0%, 19.3%, and 13.4% is achieved in m CP, m CP: i TPBIPy, and m CP:TPBI hosted blue phosphorescent organic light‐emitting diodes, respectively, indicating the superior electron‐acceptor property of the N‐linked i TPBIPy for exciplex forming cohost. Abstract : Through an isomeric N‐linkage, a new electron acceptor of 1, 1′, 1″‐(pyridine‐2, 4, 6‐triyl)tris(2‐phenyl‐1 H ‐benzo[ d ]imidazole) ( i TPBIPy) exhibits simplified synthesis, comparable energy levels, but poorer electron‐transport compared to commercial C‐linked 2, 2, 2‐(1, 3, 5‐phenylene)‐tris(1‐phenyl‐1 H ‐benzimidazole) (TPBI). However, a maximum external quantum efficiency of 19.3% is achieved in a N, N ′‐dicarbazolyl‐3, 5‐benzene ( m CP): i TPBIPy exciplex cohosted blue phosphorescent organic light‐emitting diode (OLED), which is significantly higher than 13.4% of m CP:TPBI.