Positive impact of chromophore flexibility on the efficiency of red thermally activated delayed fluorescence materials

Wang, Yuan‐Yuan; Tong, Kai‐Ning; Zhang, Kai; Lu, Chen‐Han; Chen, Xing; Liang, Jing-Xing; Wang, Chuan‐Kui; Wu, Chung‐Chih; Fung, Man‐Keung; Fan, Jian

doi:10.1039/d1mh00028d

Cited by 43 publications

(13 citation statements)

References 47 publications

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“…We envisioned that this molecular design leveraging on strong intramolecular π-stacking interactions would be able to break the efficiency limit on long wavelength TSCT-TADF emissions, as opposed to an edge-toface orientation. Herein, we designed four molecules, DPXZ-QX, DPXZ-DFQX, DPXZ-2QX, and DPXZ-2DFQX using planar dibenzo[a,c]phenazine (QX) and its fluorinated derivative (DFQX) as the acceptors (Figure 1) [42][43][44][45][46][47][48][49]. The quasiplanar O-bridged triphenylamine (DPXZ) was used as the donor [40,41,50].…”

Section: Introductionmentioning

confidence: 99%

Acceptor-Donor-Acceptor π -Stacking Boosts Intramolecular Through-Space Charge Transfer towards Efficient Red TADF and High-Performance OLEDs

et al. 2022

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Organic push-pull systems featuring through-space charge transfer (TSCT) excited states have been disclosed to be capable of exhibiting thermally activated delayed fluorescence (TADF), but to realize high-efficiency long-wavelength emission still remains a challenge. Herein, we report a series of strongly emissive orange-red and red TSCT-TADF emitters having (quasi)planar and rigid donor and acceptor segments which are placed in close proximity and orientated in a cofacial manner. Emission maxima (λem) of 594−599 nm with photoluminescence quantum yields (PLQYs) of up to 91% and delayed fluorescence lifetimes of down to 4.9 μs have been achieved for new acceptor-donor-acceptor (A-D-A) molecules in doped thin films. The presence of multiple acceptors and the strong intramolecular π-stacking interactions have been unveiled to be crucial for the efficient low-energy TSCT-TADF emissions. Organic light-emitting diodes (OLEDs) based on the new A-D-A emitters demonstrated electroluminescence with maximum external quantum efficiencies (EQEs) of up to 23.2% for the red TSCT-TADF emitters. An EQE of 18.9% at the brightness of 1000 cd m-2 represents one of the highest values for red TADF OLEDs. This work demonstrates a modular approach for developing high-performance red TADF emitters through engineering through-space interactions, and it may also provide implications to the design of TADF emitter with other colours.

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Section: Introductionmentioning

confidence: 99%

Acceptor-Donor-Acceptor π -Stacking Boosts Intramolecular Through-Space Charge Transfer towards Efficient Red TADF and High-Performance OLEDs

et al. 2022

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“…In consequence, there are only very limited reports on the efficient orange–red TADF OLEDs with highest η ext s of around 30%. [ 3 , 34 , 35 , 36 , 37 ]…”

Section: Introductionmentioning

confidence: 99%

High‐Performance Orange–Red Organic Light‐Emitting Diodes with External Quantum Efficiencies Reaching 33.5% based on Carbonyl‐Containing Delayed Fluorescence Molecules

Jiang

Líu

et al. 2021

Advanced Science

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Developing orange to red purely organic luminescent materials having external quantum efficiencies (ηexts) exceeding 30% is challenging because it generally requires strong intramolecular charge transfer, efficient reverse intersystem crossing (RISC), high photoluminescence quantum yield (ΦPL), and large optical outcoupling efficiency (Φout) simultaneously. Herein, by introducing benzoyl to dibenzo[a,c]phenazine acceptor, a stronger electron acceptor, dibenzo[a,c]phenazin‐11‐yl(phenyl)methanone, is created and employed for constructing orange–red delayed fluorescence molecules with various acridine‐based electron donors. The incorporation of benzoyl leads to red‐shifted photoluminescence with accelerated RISC, reduced delayed lifetimes, and increased ΦPLs, and the adoption of spiro‐structured acridine donors promotes horizontal dipole orientation and thus renders high Φouts. Consequently, the state‐of‐the‐art orange–red organic light‐emitting diodes are achieved, providing record‐high electroluminescence (EL) efficiencies of 33.5%, 95.3 cd A−1, and 93.5 lm W‒1. By referring the control molecule without benzoyl, it is demonstrated that the presence of benzoyl can exert significant positive effect over improving delayed fluorescence and enhancing EL efficiencies, which can be a feasible design for robust organic luminescent materials.

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“…presented a top‐performing red emitter PT‐TPA based on a rigid dithieno[3,2‐a:2',3'‐c]phenazine‐2,5‐dicarbonitrile acceptor and two ortho‐TPA donors, achieving a high EQE of 29.7% with an emission peak of 632 nm. [ 21 ] Based on these reports, it has reached a consensus to develop efficient red TADF emitters by employing multi‐ring planar acceptor and rigid donor units to restrict intramolecular rotation and vibration, thereby reducing their inherent non‐radiative transition and realizing satisfactory efficiencies in the OLEDs. [ 22‐25 ] Besides, for these reported red TADF emitters, it could be noticed that they all possess multiple donor units in the compounds which originally aimed to strengthen the intramolecular charge‐transfer (CT) transition and further enhance the molecular rigidity.…”

Section: Background and Originality Contentmentioning

confidence: 99%

Improving Efficiency of Red Thermally Activated Delayed Fluorescence Emitter by Introducing Quasi‐Degenerate Orbital Distribution

et al. 2022

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Comprehensive Summary Red thermally activated delayed fluorescence (TADF) emitters are essential for the development of organic light‐emitting diodes (OLEDs). To better understand and develop red TADF emitters, herein, the effect of quasi‐degenerate orbital distribution was investigated on their performance. Two red TADF emitters 10,10'‐(11,12‐difluorodibenzo[a,c]phenazine‐3,6‐diyl)bis(10H‐phenoxazine) (DPXZ‐BPF) and 10,10',10”‐(12‐fluorodibenzo[a,c]phenazine‐3,6,11‐triyl)tris(10H‐phenoxazine) (TPXZ‐BPF) were constructed by combining two or three phenoxazine (PXZ) donor units with a rigid coplanar acceptor core. As expected, a couple of PXZ units can induce quasi‐degenerate orbital distribution by virtue of the high steric hindrance between each donor unit and acceptor core, which enables multiple excited states engaged in the reverse intersystem crossing (RISC) process. Consequently, DPXZ‐BPF and TPXZ‐BPF exhibit fast RISC rates (kRISCs) of 1.07 × 106 s–1 and 1.29 × 106 s–1 and high PLQYs of 74.6% and 81.1%, respectively. And the higher kRISC and PLQY of TPXZ‐BPF are mainly attributed to the additional quasi‐degenerate orbitals, which further enhance the triplet RISC process and the singlet radiative process. As a result, TPXZ‐BPF‐based OLEDs achieved improved efficiencies with a red‐shifted emission compared with DPXZ‐BPF‐based OLEDs. These results demonstrated the tremendous potential of introducing quasi‐degenerate orbital distribution in developing red TADF emitters.

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Positive impact of chromophore flexibility on the efficiency of red thermally activated delayed fluorescence materials

Abstract: Rigid electron donors (D) and acceptors (A) have been widely used in recent years for the construction of D-A type thermally activated delayed fluorescence (TADF) materials. However, the chromophore robustness...

Cited by 43 publications

References 47 publications

Acceptor-Donor-Acceptor π -Stacking Boosts Intramolecular Through-Space Charge Transfer towards Efficient Red TADF and High-Performance OLEDs

Acceptor-Donor-Acceptor π -Stacking Boosts Intramolecular Through-Space Charge Transfer towards Efficient Red TADF and High-Performance OLEDs

High‐Performance Orange–Red Organic Light‐Emitting Diodes with External Quantum Efficiencies Reaching 33.5% based on Carbonyl‐Containing Delayed Fluorescence Molecules

Improving Efficiency of Red Thermally Activated Delayed Fluorescence Emitter by Introducing Quasi‐Degenerate Orbital Distribution

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