Matrix‐Free Hyperfluorescent Organic Light‐Emitting Diodes Based on Carbene–Metal–Amides

Cho, Hwanhee; Romanov, Alexander S.; Bochmann, Manfred; Credgington, Dan

doi:10.1002/adom.202001965

Cited by 25 publications

(28 citation statements)

References 47 publications

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“…Carbene‐metal‐amides (CMAs) [ 1–18 ] have recently emerged as a new type of donor‐bridge‐acceptor materials demonstrating unity luminescence quantum yields and short excited state lifetime (<1 µs) and show great promise for realizing energy efficient organic light‐emitting diodes (OLEDs). The molecular design of CMA emitters is reminiscent of the donor–acceptor strategy applied in organic thermally activated delayed fluorescence (TADF) materials.…”

Section: Introductionmentioning

confidence: 99%

“…Carbene-metal-amides (CMAs) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] have recently emerged as a new type of donor-bridge-acceptor materials demonstrating unity luminescence quantum yields and short excited state lifetime (<1 µs) and show great promise for realizing energy efficient organic light-emitting diodes (OLEDs). The molecular conversion between 1 CT and 3 CT states requires involvement of a 3 LE state [23][24][25] ideally resonant with the manifold of the CT states.…”

Section: Introductionmentioning

confidence: 99%

“…However, OLED devices made from a series of such modified CMA variants show the limitations of this approach due to decreased operational device lifetimes which correlates with increase of the emission lifetime while the emission blue-shifts for CMA material. [4][5][6] The doubly-substituted blue CF 3 -CMA material shown in Figure 1 possesses a relatively long emission lifetimes of up to 11.5 µs, comparable to organic TADF emitters. Such slow emission is linked to the 3 LE state having a lower energy than the manifold of the CT states.…”

Section: Introductionmentioning

confidence: 99%

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Donor N‐Substitution as Design Principle for Fast and Blue Luminescence in Carbene‐Metal‐Amides

Reponen

Chotard

Lempelto

et al. 2022

Advanced Optical Materials

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design of CMA emitters is reminiscent of the donor-acceptor strategy applied in organic thermally activated delayed fluorescence (TADF) materials. [19,20] Organic TADF materials have attracted enormous research interest since Adachi et al. showed they could be used in high-efficiency OLED devices. [20] Unlike organic TADF emitters, the carbene (acceptor) and amide (donor) ligands in CMA materials are bridged by a coinage metal atom that not only enables rotational flexibility between donor and acceptor but also, by virtue of its spin-orbit coupling (SOC) coefficient, greatly accelerates intersystem crossing (ISC) rates, leading to short excited state lifetimes. Since the highest occupied molecular orbital (HOMO) is mainly localized on the amide and the LUMO on the carbene and both are thus spatially decoupled, this molecular design minimizes the exchange energy between emissive intramolecular charge-transfer (CT) states and promotes efficient reverse ISC (rISC) between singlet and triplet states of CT character. [9,10] The computations on gold-centered CMAs have indicated a direct 1 CT-3 CT pathway enabled by strong SOC from the metal bridge. Conversely, the presence of a nearby locally excited triplet state ( 3 LE) slows down emission kinetics. [9,10] This finding contrasts with one of the current interpretations of emission in organic TADF materials [21,22] where it has been proposed that A series of gold-centered carbene-metal-amide (CMA) complexes are synthesized with the carbazole donor ligand modified by substitution with nitrogen atoms in varying positions. The luminescence of new aza-CMA complexes shows a significant blueshift depending on the position of the N atom, to provide bright blue-green (500 nm), sky-blue (478 nm), blue (450 nm) and deep-blue (419 nm) light-emitters. The impact of the electron-withdrawing aza-group on the nature of the luminescence and the excited state energies of the locally excited (LE) or charge transfer (CT) states have been interpreted with the help of transient absorption, in-depth photoluminescence experiments and theoretical calculations. By considering the orbital characters of the lowest CT and LE states, we develop a new concept for simultaneous energy tuning for both of these states with a single aza-substitution, allowing for fast and blue CT emission. This concept allows the interference of 3 LE phosphorescence to be avoided at room temperature. The approach is extended to two N substitutions at the optimal location in the 3-and 6-positions of the carbazole skeleton. These results suggest a practical molecular design towards the development of bright and deep-blue emitting CMA materials to tackle the stability problem of energy-efficient deep-blue OLEDs.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Donor N‐Substitution as Design Principle for Fast and Blue Luminescence in Carbene‐Metal‐Amides

Reponen

Chotard

Lempelto

et al. 2022

Advanced Optical Materials

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“…[27,28] Accordingly, the carbene-metal-amide complexes usually have very quick k RISC (≈10 7 s −1 ) (Figure 1b), making them promising candidates as TADF sensitizers. [23,29] Herein, we proposed an effective approach of employing a carbene-Cu(I)-amide, (MAC*)Cu(Cz), [30] as a TADF sensitizer for fluorescent and TADF OLEDs. (MAC*)Cu(Cz) was selected for its extremely fast k RISC of around 10 7 s −1 due to the intrinsically strong SOC.…”

Section: Introductionmentioning

confidence: 99%

“…[ 27,28 ] Accordingly, the carbene‐metal‐amide complexes usually have very quick k RISC (≈10 7 s −1 ) (Figure 1b), making them promising candidates as TADF sensitizers. [ 23,29 ]…”

Section: Introductionmentioning

confidence: 99%

Copper(I) Complex as Sensitizer Enables High‐Performance Organic Light‐Emitting Diodes with Very Low Efficiency Roll‐Off

Zhan

et al. 2021

Adv Funct Materials

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Organic light-emitting diodes (OLEDs) utilizing purely organic thermally activated delayed fluorescence (TADF) sensitizers have recently achieved high efficiencies and narrow-band emissions. However, these devices still face intractable challenges of severe efficiency roll-off at practical luminance and finite operational lifetime. Herein, a carbene-Cu(I)-amide complex, (MAC*)Cu(Cz), is demonstrated as a TADF sensitizer for both fluorescent and TADF OLEDs. The (MAC*)Cu(Cz)sensitized fluorescent OLED not only achieves a high external quantum efficiency (EQE) of 14.6% with an extremely low efficiency roll-off of 12% at the high luminance of 10 000 nits, but also delivers a 15 times longer operational lifetime than that of the non-sensitized reference device. More importantly, utilizing the (MAC*)Cu(Cz) sensitizer in the multi-resonance (MR) TADF OLED results in a record-high EQE of 26.5% together with a full-width at half maximum of 46 nm and an emission peak at 566 nm. This value is the state-of-the-art efficiency for yellow-emitting MR-TADF OLEDs. The photophysical analysis proved that the fast reverse intersystem crossing process of (MAC*)Cu(Cz) is the key factor to suppress triplet exciton involved quenching at high luminance. This finding firstly demonstrates the use of Cu(I) complex as an efficient TADF sensitizer and paves the way for practical applications of TADF sensitized OLEDs.

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Efficient and Bright Organic Radical Light‐Emitting Diodes with Low Efficiency Roll‐Off

Cho,

Gorgon,

Hung

et al. 2023

Advanced Materials

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Organic radicals have been of interest due to their potential to replace nonradical‐based organic emitters, especially for deep red/near‐infrared (NIR) electroluminescence (EL), based on the spin‐allowed doublet fluorescence. However, the performance of the radical‐based EL devices is limited by low carrier mobility that causes a large efficiency roll‐off at high current densities. Here, we report highly efficient and bright doublet EL devices by combining a thermally activated delayed fluorescence (TADF) host that supports both electron and hole transport and a tris(2,4,6‐trichlorophenyl)methyl‐based radical emitter. Steady‐state and transient photophysical studies reveal the optical signatures of doublet luminescence mechanisms arising from both host and guest photoexcitation. The host system presented here allows balanced hole and electron currents, and we report a high maximum external quantum efficiency (EQE) of 17.4% at 707 nm peak emission with substantially improved efficiency roll‐off: over 70% of the maximum EQE (12.2%) is recorded at 10 mA cm−2, and even at 100 mA cm−2, nearly 50% of the maximum EQE (8.4%) is maintained. Charge recombination is primarily at the radical guest sites, but there is evidence from magneto‐EL for host recombination and later energy transfer to the radical guest. We consider this is an important step to the practical application of organic radicals to NIR light‐emitting devices.This article is protected by copyright. All rights reserved

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Matrix‐Free Hyperfluorescent Organic Light‐Emitting Diodes Based on Carbene–Metal–Amides

Cited by 25 publications

References 47 publications

Donor N‐Substitution as Design Principle for Fast and Blue Luminescence in Carbene‐Metal‐Amides

Donor N‐Substitution as Design Principle for Fast and Blue Luminescence in Carbene‐Metal‐Amides

Copper(I) Complex as Sensitizer Enables High‐Performance Organic Light‐Emitting Diodes with Very Low Efficiency Roll‐Off

Efficient and Bright Organic Radical Light‐Emitting Diodes with Low Efficiency Roll‐Off

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