Novel deep-blue hot exciton material for high-efficiency nondoped organic light-emitting diodes

Xu, Pei; Xu, Lei; Pan, Yuyu; Yang, Dezhi; Ma, Zetong; Qiao, Xianfeng; Hu, Dehua; Ma, Dongge; Ma, Yuguang

doi:10.1039/d2tc00877g

Cited by 15 publications

(7 citation statements)

References 28 publications

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“…For the past several years, a series of anthracene‐based blue “hot exciton” materials have been reported. [ 13 ] As shown in Figure , the anthracene core has a delicate alignment of energy levels, which is beneficial to the hRISC process. The introductions of proper donors or acceptors to anthracene could further modulate the excited‐state properties, such as the transition orbital characters of T n and S m states and the S m – T n energy gap, which promote the hRISC process.…”

Section: Introductionmentioning

confidence: 99%

Pyrene‐Based Emitters with Ultrafast Upper‐Level Triplet–Singlet Intersystem Crossing for High‐Efficiency, Low Roll‐Off Blue Organic Light‐Emitting Diode

Pan

et al. 2022

Advanced Optical Materials

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The biggest challenge is how to improve the efficiency of OLEDs and simultaneously maintain the device stability at high luminance/current density. As for conventional fluorescence materials, only 25% of singlet excitons can be utilized according to spin statistics, which leads to low device efficiency. [2] To harvest other 75% triplet excitons, the new generation of pure organic emitter materials, including thermally activated delayed fluorescence (TADF), [3] triplet-triplet annihilation (TTA), [4] and "hot exciton" materials, [5] have been developed to improve the exciton utilization by converting the triplet excitons to singlet excitons. Nevertheless, during the electroluminescence (EL) process, the accumulation of long-lived triplet excitons usually results in triplet-triplet and/or triplet-singlet quenching, and in turn, the device efficiency suffers serious roll-off, especially at high current density. [6] In addition, these high-activity lowest triplet excited state (T 1 ) excitons adversely influence the surrounding organic materials, leading to material degradation. Thus, the effective way to solve this problem is to accelerate the conversion of triplet to singlet manifold to avoid triplet excitons accumulation.As for conventional TADF materials, a donor-acceptor (D-A)-type molecular design strategy is usually adopted to realize the spatial separation of frontier molecular orbital (FMO), which endows the materials with an extremely small splitting energy between the lowest singlet (S 1 ) and triplet excited states (ΔE ST ). [7] However, the same charge transfer (CT) character of the S 1 ( 1 CT) and T 1 ( 3 CT) states often leads to negligible spin-orbit coupling (SOC) (usually less than 0.1 cm −1 ), which makes the reverse intersystem crossing (RISC) from T 1 to S 1 slow. [8] Thus, the RISC rate constants are usually <10 6 s −1 for most TADF emitters, and the efficiencies of corresponding devices seriously dropped even at low luminance intensity of <1000 cd m −2 . [9] Although great efforts have been made to promote RISC rates, stable TADF-based blue OLEDs are still rarely reported. [10] Different from the TADF materials with the RISC process from T 1 to S 1 , materials with a "hot exciton" mechanism have been proposed that can also theoretically achieve 100% exciton utilization efficiency (EUE) through the RISC process from the high-lying triplet states (T n , n ≥ 2) to the singletstate (S m , m ≥ 1) (hRISC). [11] Compared to the RISC process of The reverse intersystem crossing (RISC) process from triplet to singlet manifold can efficiently improve the efficiencies of organic light-emitting diodes (OLEDs). The relevant RISC rate (k RISC ) is one of the key factors that affect the efficiency roll-off and stability of devices. Here, a new blue "hot exciton" material, CPPCN, with pyrene as the core, is designed and synthesized. Photophysical studies indicate there are multiple high-lying triplet states near the lowest singlet excited state (S 1 ) of CPPCN, which facilitate the RISC from the high-lying...

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Section: Introductionmentioning

confidence: 99%

Pyrene‐Based Emitters with Ultrafast Upper‐Level Triplet–Singlet Intersystem Crossing for High‐Efficiency, Low Roll‐Off Blue Organic Light‐Emitting Diode

Pan

et al. 2022

Advanced Optical Materials

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“…[15] In traditional TADF, the reverse intersystem crossing rate (RISC) occurs from the first excited low-lying triplet state T 1 to the singlet state S 1 , but in the "hot exciton" mechanism the RISC occurs perhaps not from the low-lying triplet, it also occurs from higher excited triplet states. [16,17] Considerably, in conventional TADF emitter, the mechanism involves the transition from the (S 1 -T 1 ) state which is referred to as "cold exciton". [18] In contrast, the "hot exciton" mechanism follows the conversion from the higher-lying triplet, (T n , n > 2) states and singlet (S m , m > 1) states.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Fast RISC in Hot‐Exciton Thermally Activated Delayed Fluorescence Emitter Through Fused Ring Modification: A Theoretical Insights

Nathiya

2024

Advcd Theory and Sims

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Recent progress has shown promising advancements in enhancing the Reverse intersystem crossing (RISC) process between high‐energy triplet states (Tn, n ≥ 1) and radiative singlet states (Sm) through the utilization of the classic D‐A‐D' strategy. In this study, 12 molecules employing phenyl carbazole and a peripheral phenanthroimidazole as the donors and fused cores as acceptors are theoretically designed. Additionally, electron‐withdrawing groups such as fluorine and cyano, as well as electron‐donating group like methoxy, are incorporated into anthracene, napthaoxadiazole, and napthothiadiazole derivatives, acting as fused core components. Theoretical analyses reveal that among the molecules examined, eight adhere to the three golden principle rules, demonstrating a large energy gap between S1‐T1, the minimal ΔES1‐T2, and large T2‐T1. Additionally, these molecules exhibit significant Spin‐orbit coupling (SOC) and maintain a strong Hybridized local and charge transfer (HLCT) character, facilitating the fast hRISC from T2 to S1. The auxiliary inclusion of heteroatoms, such as oxygen and sulfur, on the anthracene core, aligns with the prerequisite strategy, ultimately reinforcing the SOC. Furthermore, replacing the methoxy group on the Nz bridge significantly enhances the SOC, resulting in a substantial increase in the hRISC rate (10 +08 s−1). Overall, the findings substantially elevate the photophysical attributes of the designed molecules through the utilization of the hRISC channel.

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“…However, the IQE in these hot exciton materials is still far from the upper limitation of 100% because the EUE and PLQY cannot reach 100% simultaneously (see Figure S1). ,− Namely, these empirical rules hardly produce an excellent IQE for hot exciton materials, owing to the rudimentary understanding of the EUE and PLQY. Therefore, it is urgent to unravel the underlying mechanisms and establish theoretical rules to promote the IQE of hot exciton materials.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Descriptors for High-Throughput Screening of Efficient Electro-Fluorescent Materials

Qian

et al. 2023

Chem. Mater.

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Electro-fluorescent materials with 100% internal quantum efficiency (IQE) and short fluorescence lifetimes (τf, ∼ ns) are desirable and achievable by harvesting high-lying triplet excitons. However, the IQE governed by exciton utilization efficiency (EUE) and photoluminescence quantum yield (PLQY) remains low. Herein, from the electro-fluorescence process involving triplet excitons and energy gap law, we established two excited-state descriptors (triplet–triplet energy gap ΔE TT and oscillator strength f) to characterize EUE, PLQY and τf, by taking a series of hot exciton compounds as prototypes. Subsequently, these descriptors were employed to perform high-throughput screening of over 5000 fluorophores, predicting 19 candidate molecules with a high IQE (>90%). We stressed that the large values of these descriptors are conducive to high EUE and PLQY and short τf. This work presents a guideline to design and screen efficient electro-fluorescent materials beyond the spin-statistical limit.

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Novel deep-blue hot exciton material for high-efficiency nondoped organic light-emitting diodes

Abstract: The reverse intersystem crossing (RISC) process conducted from high-energy triplet states (Tn, n ≥ 2) to singlet state (Sm, m ≥ 1), termed as hot exciton process, has been confirmed...

Cited by 15 publications

References 28 publications

Pyrene‐Based Emitters with Ultrafast Upper‐Level Triplet–Singlet Intersystem Crossing for High‐Efficiency, Low Roll‐Off Blue Organic Light‐Emitting Diode

Pyrene‐Based Emitters with Ultrafast Upper‐Level Triplet–Singlet Intersystem Crossing for High‐Efficiency, Low Roll‐Off Blue Organic Light‐Emitting Diode

Enhancing Fast RISC in Hot‐Exciton Thermally Activated Delayed Fluorescence Emitter Through Fused Ring Modification: A Theoretical Insights

Excited-State Descriptors for High-Throughput Screening of Efficient Electro-Fluorescent Materials

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