Activating Energy Transfer Tunnels by Tuning Local Electronegativity of Conjugated Polymeric Backbone for High‐Efficiency OLEDs with Low Efficiency Roll‐Off

Zhao, Zhennan; Liu, Yuchao; Hua, Lei; Yan, Shouke; Ren, Zhongjie

doi:10.1002/adfm.202200018

Cited by 22 publications

(24 citation statements)

References 51 publications

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“…Meanwhile, the intersystem crossing process of the excited states can probably be tuned and thus enhance spin-orbit coupling (SOC) between singlet and triplet states and light-emitting efficiency according to Fermi's golden rule [38][39][40][41] . In practice, modulating the energy levels of excited states to enhance the efficiency has been implemented in blue-green emitters [42][43][44][45] . There are, however, few reports on the regulation of intersystem crossing processes of orangered light emitters.…”

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confidence: 99%

Constructing high-efficiency orange-red thermally activated delayed fluorescence emitters by three-dimension molecular engineering

Hua

Liu

et al. 2022

Nat Commun

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Preparing high-efficiency solution-processable orange-red thermally activated delayed fluorescence (TADF) emitters remains challenging. Herein, we design a series of emitters consisting of trinaphtho[3,3,3]propellane (TNP) core derivatized with different TADF units. Benefiting from the unique hexagonal stacking architecture of TNPs, TADF units are thus kept in the cavities between two TNPs, which decrease concentration quenching and annihilation of long-lived triplet excitons. According to the molecular engineering of TADF and host units, the excited states can further be regulated to effectively enhance spin-orbit coupling (SOC) processes. We observe a high-efficiency orange-red emission at 604 nm in one instance with high SOC value of 0.862 cm−1 and high photoluminescence quantum yield of 70.9%. Solution-processable organic light-emitting diodes exhibit a maximum external quantum efficiency of 24.74%. This study provides a universal strategy for designing high-performance TADF emitters through molecular packing and excited state regulation.

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confidence: 99%

Constructing high-efficiency orange-red thermally activated delayed fluorescence emitters by three-dimension molecular engineering

Hua

Liu

et al. 2022

Nat Commun

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“…pBP-PTZ and pBP-PXZ with sulfurand oxygen-containing donors in the polymeric backbones, respectively, are investigated. 4 The electron-withdrawing atoms with a stronger electronegativity have a significant impact on the electronic structures of polymeric emitters. As the electro- negativity of the embedded atoms increases, the delocalization range of HOMO continuously narrows.…”

Section: Of the Conjugated Polymeric Backbones By Copolymerizing The ...mentioning

confidence: 99%

Regulating the Nature of Triplet Excited States of Thermally Activated Delayed Fluorescence Emitters

2023

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Conspectus Characterized by the reverse intersystem crossing (RISC) process from the triplet state (T1) to the singlet state (S1), thermally activated delayed fluorescence (TADF) emitters, which produce light by harvesting both triplet and singlet excitons without noble metals, are considered to be third-generation organic electroluminescent materials. Rapid advances in molecular design criteria, understanding the photophysics underlying TADF, and applications of TADF materials as emitters in organic light-emitting diodes (OLEDs) have been achieved. Theoretically, enhanced spin–orbit coupling (SOC) between singlet and triplet states can result in a fast RISC process and thus a high light-emitting efficiency according to Fermi’s golden rule. Therefore, regulating the nature of triplet excited states by elaborate molecular design to improve SOC is an effective approach to high-efficiency TADF-based OLEDs. Generally, on one hand, the increased local excited (LE) populations of the excited triplet state can significantly improve the nature flips between S1 and T1. On other hand, the reduced energy gap between S1 and the lowest triplet with a charge transfer (CT) characteristic can also enhance their vibronic coupling. Consequently, it is vital to determine how to regulate the nature of triplet excited states by molecular design to guide the material synthesis, especially for polymeric emitters. In this Account, we focus on modulating the strategy of triplet excited states for TADF emitters and an in-depth understanding of the photophysical processes, leading to optimized OLED device performance. We include several kinds of strategies to control the nature of triplet excited states to guide the synthesis of small-molecule and polymer TADF emitters: (1) Modulating the electronic distribution of conjugated polymeric backbones by copolymerizing the electron-donating host: accordingly, the nature of excited states can be changed, especially for triplets. Meanwhile, the utilization of excitons can be systematically improved by adjusting the electronic structure of triplet states with long-range distribution in the conjugated polymeric backbones. (2) Halogenating acceptors of TADF units: the introduced halogen atoms would reestablish the electronic distribution of the triplet and relocate the hole orbits, resulting in a CT and LE hybrid nature of a triplet transformed into a LE-predominant state, which favors the RISC process. (3) Stereostructure regulation: by constructing a diverse arrangement of three-dimensional spatial configurations or conjugated architectures, the nature of the triplet can also be finely tuned, such as hyperbranched structures with multiple triplet–singlet vibration couplings, half-dendronized–half-encapsulated asymmetric systems, trinaphtho[3,3,3] propeller-based three-dimensional spatial interspersed structures, intramolecular close-packed donor–acceptor systems, and so on. We hope that this Account will provide insights into new structures and mechanisms for achieving high-performance OLEDs base...

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“…Besides, our prior research has demonstrated that the energy transfer process from hosts to TADF units would be enhanced through adjusting the local electronegativity of the polymeric backbones by inserting electron-withdrawing atoms. Strongly electronegative atoms located on the branched chains can activate the advantageous tunnels of hole transportation from the hosts to TADF cores, which are beneficial in realizing further optimization of the efficiency roll-off . Under a rational regulation of TADF unit ratio, the HCP with 7.5% TADF cores (HCP-7.5%) performs the best device performance.…”

Section: Introductionmentioning

confidence: 99%

“…Strongly electronegative atoms located on the branched chains can activate the advantageous tunnels of hole transportation from the hosts to TADF cores, which are beneficial in realizing further optimization of the efficiency rolloff. 27 Under a rational regulation of TADF unit ratio, the HCP with 7.5% TADF cores (HCP-7.5%) performs the best device performance. The corresponding nondoped PLED device achieves a red emission with an EQE max of 8.39% and exhibits no roll-off when the luminance is less than 100 cd/m 2 and only 3.3% decrease at 500 cd/m 2 .…”

Section: ■ Introductionmentioning

confidence: 99%

Hyperbranched Conjugated Polymer with Multiple Charge Transfer Enables High-Efficiency Nondoped Red Electroluminescence with Low Driving Voltage

Zhao

Tong

Liu

et al. 2023

ACS Appl. Mater. Interfaces

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Conjugated polymers featuring thermally activated delayed fluorescence (TADF) attract tremendous attention in both academic and industry communities due to their easy solution processing for fabricating large-area and low-cost high-performance polymer light-emitting diodes (PLEDs). However, current nondoped solution-processed PLEDs frequently encounter significant efficiency roll-offs and unreasonably high operating voltages at high brightness, especially for red-emitting polymers. Herein, we design hyperbranched conjugated polymers (HCPs) with D−A−D type TADF characteristics for high-performance red-emitting PLEDs. Multiple intramolecular charge transfer (ICT) channels induced by quasi-equivalent donors of the TADF core strongly boost the reverse intersystem crossing (RISC) process and singlet excitons radiative transition. Coupling with the efficient energy transfer process generated by structure advantages of HCPs, the strongly electron-withdrawing oxygen atoms located on the TADF cores further accelerate hole transportation from the host chains to the TADF cores. Under a rational regulation of the TADF core ratio, the related nondoped red-emitting device performs an outstanding performance with an EQE max of 8.39% and exhibits no roll-off while the luminance is less than 100 cd/m 2 and only 3.3% decrease at 500 cd/m 2 . Simultaneously, the EQE can maintain 7.4% under 1000 cd/m 2 . Furthermore, the corresponding nondoped device exhibits a low turn-on voltage of around 2.5 V and achieves a luminance of 500 cd/m 2 at 3.5 V and even 1000 cd/m 2 at 3.9 V. To our knowledge, this is the best performance among all nondoped red PLEDs with high brightness obtained at low operating voltage.

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Activating Energy Transfer Tunnels by Tuning Local Electronegativity of Conjugated Polymeric Backbone for High‐Efficiency OLEDs with Low Efficiency Roll‐Off

Cited by 22 publications

References 51 publications

Constructing high-efficiency orange-red thermally activated delayed fluorescence emitters by three-dimension molecular engineering

Constructing high-efficiency orange-red thermally activated delayed fluorescence emitters by three-dimension molecular engineering

Regulating the Nature of Triplet Excited States of Thermally Activated Delayed Fluorescence Emitters

Hyperbranched Conjugated Polymer with Multiple Charge Transfer Enables High-Efficiency Nondoped Red Electroluminescence with Low Driving Voltage

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