Tetrabenzo[<i>a</i>,<i>c</i>]phenazine Backbone for Highly Efficient Orange–Red Thermally Activated Delayed Fluorescence with Completely Horizontal Molecular Orientation

Balijapalli, Umamahesh; Lee, Yi Ting; Karunathilaka, Buddhika S. B.; Tumen‐Ulzii, Ganbaatar; Auffray, Morgan; Tsuchiya, Youichi; Nakanotani, Hajime; Adachi, Chihaya

doi:10.1002/anie.202106570

Cited by 77 publications

(47 citation statements)

References 74 publications

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“…The distinct difference in transition nature between S 1 and T 1 states is beneficial for the occurrence of RISC processes, rendering increased RISC rate. [22,[42][43][44] In contrast, the second triplet excited (T 2 ) and third triplet excited (T 3 ) states of both molecules are dominated by the CT characters. Theoretically, upconversion of CT-featured triplet states to CT-featured singlet states is difficult.…”

Section: Resultsmentioning

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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Section: Resultsmentioning

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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“…Consequently, two horizontal-oriented structure-based emitters were developed by Adachi et al in 2021. [33] The red emitters, PQ2 and PQ3, were synthesized by directly attaching cyano units with a phenyl spacer on a rigid phenazine acceptor. The PLQY of both emitters was 38, and 51 % for PQ2 and PQ3, respectively, a separation between two acceptors enhances the PLQY while maintaining similar TADF properties.…”

Section: Chemistry-a European Journalmentioning

confidence: 99%

Molecular Design Strategy for Orange Red Thermally Activated Delayed Fluorescence Emitters in Organic Light‐Emitting Diodes (OLEDs)

Naveen

Prabhu

Braveenth

et al. 2022

Chemistry A European J

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Pure organic molecules based thermally activated delayed fluorescence (TADF) emitters have been successfully developed in recent years for their propitious application in highly efficient organic light emitting diodes (OLEDs). In the case of orange red emitters, the non-radiative process is known to be a serious issue due to its lower lying singlet energy level. However, recent studies indicate that there are tremendous efforts put to develop efficient orange red TADF emitters. In addition, the external quantum efficiency (EQE) of heteroaromatic based orange red TADF OLEDs surpassed 30 %. Such heteroaromatic type emitters showed wide emission spectra; therefore, more attention is being paid to develop highly efficient orange red TADF emitters along with good color purity. Herein, the recent progress of orange red TADF emitters based on molecular structures, such as cyanobenzene, heteroaromatic, naphthalimide, and boronbased acceptors, are reviewed. Further, our insight on these acceptors has been provided by their photophysical studies and device performances. Future perspectives of orange red TADF emitters for real practical applications are discussed.[a] K.

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“…Such resonance cases lead both states to evidently contribute the phosphorescence spectra. [ 17 ] The corresponding apparent T 1 states show their mixed characteristics. With further increasing the concentrations (i.e., 45 wt% and higher), their phosphorescence spectra proceed with redshifts and the profiles become structureless, indicating their 3 LE states can hardly contribute to the T 1 states.…”

Section: Resultsmentioning

confidence: 99%

Optimizing Intermolecular Interactions and Energy Level Alignments of Red TADF Emitters for High‐Performance Organic Light‐Emitting Diodes

Chen

Wang

Xiao

et al. 2022

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Adequately harvesting all excitons in a single molecule and inhibiting exciton losses caused by intermolecular interactions are two important factors for achieving high efficiencies thermally activated delayed fluorescence (TADF). One potential approach for optimizing these is to tune alignment of various excited state energy levels by using different doping concentrations. Unfortunately, emission efficiencies of most TADF emitters decrease rapidly with concentrations which limits the window for energy level tunning. In this work, by introducing a spiro group to increase steric hindrance of a TADF emitter (BPPXZ) with a phenoxazine and a dibenzo[a,c]phenazine, emission efficiency of the resulting molecule (BPSPXZ) is much less affected by concentration increase. This enables exploitation of the concentration effects to tune energy levels of its excited states for obtaining simultaneously small singlet–triplet energy offset and large spin–orbital coupling, leading to high‐efficiency reverse intersystem crossing. With these merits, organic light‐emitting diodes (OLEDs) using the BPSPXZ emitter from 5 to 60 wt% doping can all deliver EQE of over 20%. More importantly, record‐high EQEs of 33.4% and 15.8% are respectively achieved in the optimized and nondoped conditions. This work proposes a strategy for developing red TADF emitters by optimizing the intermolecular interaction and energy level alignments to facilitate exciton utilization over wide doping concentrations.

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Tetrabenzo[a,c]phenazine Backbone for Highly Efficient Orange–Red Thermally Activated Delayed Fluorescence with Completely Horizontal Molecular Orientation

Cited by 77 publications

References 74 publications

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

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

Molecular Design Strategy for Orange Red Thermally Activated Delayed Fluorescence Emitters in Organic Light‐Emitting Diodes (OLEDs)

Optimizing Intermolecular Interactions and Energy Level Alignments of Red TADF Emitters for High‐Performance Organic Light‐Emitting Diodes

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