Multiplying the efficiency of red thermally activated delayed fluorescence emitter by introducing intramolecular hydrogen bond

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 448; p. 137717
• Main Authors: Yang, Hao-Yu, Zhang, Heng-yuan, Zhang, Ming, Fan, Xiao-chun, Lin, Hui, Tao, Si-Lu, Zheng, Cai-Jun, Zhang, Xiao-Hong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.11.2022
• Subjects: Intramolecular hydrogen bond; Non-radiative decay; Radiative process; Red organic light-emitting diodes; Thermally activated delayed fluorescence; Red organic light-emitting diodes; Thermally activated delayed fluorescence; Radiative process; Non-radiative decay; Intramolecular hydrogen bond
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2022.137717

[Display omitted] •Three TADF emitters were synthesized by finely modifying the acceptor units.•The donor–acceptor intramolecular hydrogen bond is formed in TPA-APm.•TPA-APm exhibits both twofold higher kF and an order of magnitude lower knr.•TPA-APm-based red OLEDs achieved multiply increasing efficiency >20%. As one of the three primary colors, red organic light-emitting diodes (OLEDs) are indispensable in practical applications. However, red emitters are generally subject to severe non-radiative exciton loss due to their narrow energy gap. In this work, three new thermally activated delayed fluorescence (TADF) emitters were developed, namely 4-(acenaphtho[1,2-b]quinoxalin-9-yl)-N,N-diphenylaniline (TPA-AP), 4-(acenaphtho[1,2-b]pyrido[2,3-e]pyrazin-10-yl)-N,N-diphenylaniline (TPA-APy), and 4-(acenaphtho[1,2-b]pyrazino[2,3-e]pyrazin-9-yl)-N,N-diphenylaniline (TPA-APm), employing a series of finely modified acenaphtho[1,2-b]quinoxaline (AP) derivatives as acceptor units. Among three TADF emitters, an intramolecular hydrogen bond is formed between the donor (D) and acceptor (A) units in TPA-APm. Consequently, the overlap of the frontier molecular orbitals (FMOs) of TPA-APm can increase appropriately, and the fluorescence radiative rate (kF) of TPA-APm is nearly twofold than that of TPA-AP and TPA-APy. Furthermore, the non-radiative decay rate (knr) of TPA-APm is less than that of TPA-AP and TPA-APy by an order of magnitude, which is attributed to the improved molecular rigidity caused by intramolecular hydrogen bond. As a result, TPA-APm-based OLEDs achieved a multiplied external quantum efficiency (EQE) of 21.1% with the electroluminescence peak at 590 nm, comparing to only 7.0% and 11.5% for the TPA-AP-based and TPA-APy-based devices, respectively. These results demonstrate appropriate intramolecular hydrogen bond can suppress the influence of non-radiative decay by simultaneously enhancing molecular rigidity and facilitating the fluorescence process, and have great potential in the design of efficient red TADF emitters.