Developing Through‐Space Charge Transfer Polymers as a General Approach to Realize Full‐Color and White Emission with Thermally Activated Delayed Fluorescence

Hu, Jun; Li, Qiang; Wang, Xingdong; Shao, Shiyang; Jing, Xiabin; Wang, Fosong

doi:10.1002/anie.201902264

Cited by 213 publications

(183 citation statements)

References 35 publications

(53 reference statements)

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“…Purely organic donor/acceptor (D/A) compounds constructed by a conjugated linker is an effective strategy for designing thermally activated delayed fluorescence (TADF) materials, which have great potential to replace phosphorescent materials based on rare metal (like iridium or platinum) complexes in organic light‐emitting diodes (OLEDs) . In this kind of so‐called D‐π‐A structures, the intramolecular charge transfer can take place through covalent bond (TBCT) . By carefully modulating the twisted angle between donor and acceptor as well as their relative intensities, the singlet‐triplet splitting energy (D E ST ) of the D‐π‐A compounds can be reduced .…”

Section: Introductionmentioning

confidence: 99%

Through Space Charge Transfer for Efficient Sky‐Blue Thermally Activated Delayed Fluorescence (TADF) Emitter with Unconjugated Connection

Wang

Huang

et al. 2019

Advanced Optical Materials

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which have great potential to replace phosphorescent materials based on rare metal (like iridium or platinum) complexes in organic light-emitting diodes (OLEDs). [2] In this kind of so-called D-π-A structures, the intramolecular charge transfer can take place through covalent bond (TBCT). [3] By carefully modulating the twisted angle between donor and acceptor as well as their relative intensities, the singlet-triplet splitting energy (DE ST ) of the D-π-A compounds can be reduced. [4] Then, the reverse intersystem crossing (RISC) process can promote the triplet excitons up to the singlet low-lying state at due to such small DE ST after photo-or electroexcitation. Therefore, 100% internal quantum efficiency (IQE) can be theoretically achieved in OLEDs. Following this strategy, the D-π-A type TADF emitters covering R-G-B even the near infrared regions have been extensively studied. [5] Another way for small DE ST in TADF materials is to separate D/A moieties in unconjugated structures because the isolated D and A would result in a small overlap of highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) for small electron exchange energy. [1d,6] Such D-σ-A type TADF emitters can be constructed by spiro junction, xanthene, triptycene, poly-styrene, etc., [7] and the relative intramolecular charge transfer process is through space (TSCT). [8] However, most of them exhibit mode rate photoluminescence quantum yield (PLQY) and relatively low electroluminescence especially in blue OLEDs. [9] Thus, the design paradigm of D-σ-A type TADF molecules still needs further investigations.In this work, we designed and synthesized a novel sky-blue spiro-type TADF emitter QAFCN, in which the donor and acceptor were not perpendicular to each other although they were connected through a spiro carbon. [5c,10] This was because the rigid donor moiety, 5,9-dihydroquinolino[3,2,1-de]acridine (QA), had a deformed conformation, which could bend the donor toward the acceptor moiety and thus shorten the D/A distance to facilitate the TSCT. [11] As compared to the classic spiro TADF emitter ACRFLCN, [9a] the QAFCN had blue-shifted emission, obviously higher PLQY and faster rate of RISC. Consequently, QAFCN-based device achieved an EQE of 17.9% Through-space charge transfer, which exists in nonconjugation linker based thermally activated delayed fluorescence (TADF) materials, excites chemists to explore more possibilities in organic light-emitting diodes (OLEDs). Herein, an sp 3 -hybrid carbon-centered donor-σ-acceptor type chromophore, QAFCN, is tentatively developed by exploring bi-acridine based electrondonor, i.e., 5,5-dimethyl-5,9-dihydroquinolino[3,2,1-de]acridine (QA). It is interesting to find that the QA moiety shows downshift in highest occupied molecular orbital because of its deformed geometry, which makes it qualified for sky-blue electroluminescence emission. Together with the blue-shift, enhanced photoluminescence quantum yield and faster reverse intersystem crossing rate are also o...

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Section: Introductionmentioning

confidence: 99%

Through Space Charge Transfer for Efficient Sky‐Blue Thermally Activated Delayed Fluorescence (TADF) Emitter with Unconjugated Connection

Wang

Huang

et al. 2019

Advanced Optical Materials

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“…Thefirst one is based on the combination of an electron donor (D) and electron acceptor (A). [16][17][18][19][20][21] That is,both Dand Aare carefully aligned at different sites to form aT ADF polymer,s uch as Da nd A simultaneously in the main chain, [16] Dand Asimultaneously in the side-chain, [17,18] or Di nt he main chain and Ai nt he side-chain [19][20][21] etc. Unlike small molecules,i ti sn ot an easy task to realize TADF at am acromolecular level because the relative distance,strength, and location of Dand Aall need to be well controlled to tune through-bond or through-space charge transfer (CT).…”

Section: Introductionmentioning

confidence: 99%

Bridging Small Molecules to Conjugated Polymers: Efficient Thermally Activated Delayed Fluorescence with a Methyl‐Substituted Phenylene Linker

Rao

Liu

et al. 2019

Angew Chem Int Ed

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Based on a “TADF + Linker” strategy (TADF=thermally activated delayed fluorescence), demonstrated here is the successful construction of conjugated polymers that allow highly efficient delayed fluorescence. Small molecular TADF blocks are linked together using a methyl‐substituted phenylene linker to form polymers. With the growing number of methyl groups on the phenylene, the energy level of the local excited triplet state (3LEb) from the delocalized polymer backbone gradually increases, and finally surpasses the charge‐transfer triplet state (3CT). As a result, the diminished delayed fluorescence can be recovered for the tetramethyl phenylene containing polymer, revealing a record‐high external quantum efficiency (EQE) of 23.5 % (68.8 cd A−1, 60.0 lm W−1) and Commission Internationale de l′Eclairage (CIE) coordinates of (0.25, 0.52). Combined with an orange‐red TADF emitter, a bright white electroluminescence is also obtained with a peak EQE of 20.9 % (61.1 cd A−1, 56.4 lm W−1) and CIE coordinates of (0.36, 0.51).

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“…The low energy gap between the singlet (S 1 ) and triplet (T 1 ) excited states (Δ E ST ≈0.2 eV) is the essential requirement to achieve an efficient delayed fluorescence by thermal upconversion (T 1 to S 1 ; RISC) . Hence, this new design strategy with appropriate molecular building units can lead to the complementary prompt and delayed fluorescence covering the entire visible region …”

Section: White Light Emission Through Harvesting Of the Triplet Statementioning

confidence: 99%

Molecular Engineering Approaches Towards All‐Organic White Light Emitting Materials

Kundu

Pallavi

et al. 2020

Chemistry A European J

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White light emitting (WLE) materials are of increasing interesto wing to their promising applicationsi na rtificial lighting, display devices, molecular sensors, and switches.I n this context,o rganic WLE materials cater to the interesto f the scientific community owing to their promising features like color purity,l ong-term stability,s olutionp rocessability, cost-effectiveness,a nd low toxicity.T he typical methodf or the generation of white light is to combine three primary (red, green, and blue) or the two complementary (e.g., yellow and blue or red and cyan) emissive units covering the whole visible spectralw indow (400-800 nm). The judicious choice of molecular buildingb locks and connecting them through either strong covalentb onds or assembling through weakn oncovalent interactions are the key to achieve enhanced emissions panning the entire visible region.In the present review article, moleculare ngineering approaches for the development of all-organic WLE materials are analyzed in view of different photophysical processes like fluorescencer esonance energy transfer (FRET), excitedstate intramolecular protont ransfer (ESIPT), charget ransfer (CT), monomer-excimer emission, triplet-state harvesting, etc. The key aspect of tuning the molecular fluorescence under the influence of pH, heat, and host-guest interactions is also discussed. The white light emission obtained from small organic molecules to supramolecular assemblies is presented,i ncluding polymers, micelles,a nd also employing covalent organic frameworks. The state-of-the-art knowledge in the field of organic WLE materials, challenges, and future scope are delineated.

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Developing Through‐Space Charge Transfer Polymers as a General Approach to Realize Full‐Color and White Emission with Thermally Activated Delayed Fluorescence

Cited by 213 publications

References 35 publications

Through Space Charge Transfer for Efficient Sky‐Blue Thermally Activated Delayed Fluorescence (TADF) Emitter with Unconjugated Connection

Through Space Charge Transfer for Efficient Sky‐Blue Thermally Activated Delayed Fluorescence (TADF) Emitter with Unconjugated Connection

Bridging Small Molecules to Conjugated Polymers: Efficient Thermally Activated Delayed Fluorescence with a Methyl‐Substituted Phenylene Linker

Molecular Engineering Approaches Towards All‐Organic White Light Emitting Materials

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