Benzimidazobenzothiazole‐Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light‐Emitting Diodes

Cui, Lin‐Song; Kim, Jong Uk; Nomura, Hiroko; Nakanotani, Hajime; Adachi, Chihaya

doi:10.1002/ange.201601136

Cited by 34 publications

(14 citation statements)

References 44 publications

(7 reference statements)

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“…Most of these carbazole-based hosts are limited to the use of blue greenish emitters since their triplet energies are below 3 eV. Hosts with less common functional groups such as cyclophosphazene (Nishimoto et al, 2014 ), silicon (Ren et al, 2004 ), and benzimidazobenzothiazole (Cui et al, 2016a ) were also developed in order to increase the triplet energy. Furthermore, trying to avoid the problem of suitable hosts, non-doped emitting layers are also under investigation by using sterically demanding molecules such as dendrimers, but they still suffer from lower efficiencies in comparison with doped emitting layers (Wong and Zysman-Colman, 2017 ; Cai and Su, 2018 ; Wei et al, 2018 ).…”

Section: Introductionmentioning

confidence: 99%

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

et al. 2020

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The synthesis of stable blue TADF emitters and the corresponding matrix materials is one of the biggest challenges in the development of novel OLED materials. We present six bipolar host materials based on triazine as an acceptor and two types of donors, namely, carbazole, and acridine. Using a tool box approach, the chemical structure of the materials is changed in a systematic way. Both the carbazole and acridine donor are connected to the triazine acceptor via a para-or a meta-linked phenyl ring or are linked directly to each other. The photophysics of the materials has been investigated in detail by absorption-, fluorescence-, and phosphorescence spectroscopy in solution. In addition, a number of DFT calculations have been made which result in a deeper understanding of the photophysics. The presence of a phenyl bridge between donor and acceptor cores leads to a considerable decrease of the triplet energy due to extension of the overlap electron and hole orbitals over the triazine-phenyl core of the molecule. This decrease is more pronounced for the para-phenylene than for the meta-phenylene linker. Only direct connection of the donor group to the triazine core provides a high energy of the triplet state of 2.97 eV for the carbazole derivative CTRZ and 3.07 eV for the acridine ATRZ. This is a major requirement for the use of the materials as a host for blue TADF emitters.

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Section: Introductionmentioning

confidence: 99%

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

et al. 2020

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“…Three main categories of host materials exist based on their different charge transport properties: hole transporting (p-type), electron transporting (n-type), and ambipolar 14 – 16 . Regardless of which type of host is used, the triplet energy of the host should be higher than that of the TADF emitter to confine the singlet and triplet excitons on the emitter molecules 17 .…”

Section: Introductionmentioning

confidence: 99%

Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts

et al. 2017

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Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.

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“…Organic light-emitting diodes (OLEDs) have garnered a significant attention due to their eco-friendly nature, low cost of production, and superior performance. − A simple architecture of OLED consists of two working electrodes sandwiching the emissive material (active layer). In OLEDs, it is important to generate the exciton (electron–hole pair) in the emissive layer.…”

Section: Introductionmentioning

confidence: 99%

Thermally Activated Delayed Fluorescence (Green) in Undoped Film and Exciplex Emission (Blue) in Acridone–Carbazole Derivatives for OLEDs

et al. 2018

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Donor−acceptor−donor materials (1,2) having acridone as acceptor unit and carbazole as donor were synthesized for optoelectronic applications. Carbazole was substituted on 2,7 positions of acridone in 1, while 3,6-trifluoromethylphenyl carbazole was substituted in 2. Steady-state and time-dependent emission properties of these compounds were studied in detail to get insight into their possible thermally activated delayed fluorescence (TADF) behavior. The singlet−triplet energy gap (ΔE ST ) was found to be as low as 0.17 eV (1) and 0.15 eV (2), favorable for TADF materials. Both these materials were found to be efficient green TADF emitters in organic light-emitting diode (OLED) devices. Interestingly, the TADF properties were observed for the first time in undoped 1,2-based devices, i.e., without host matrix, unlike the most commonly reported TADF emitters. Furthermore, an exciplex emission at 465 nm was observed in the blends of 1,2 with poly(vinylcarbazole) (PVK) in 1:7 (w/w) ratio. OLEDs with the blend of 1,2 with PVK as the active layer showed an intense electroluminescence at 465 nm matching well with the exciplex photoluminescence. Thus, we show that acridone−carbazole derivatives (1,2) offer variable electroluminescence as undoped TADF green emitter and blue exciplex emitter when doped in PVK.

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Benzimidazobenzothiazole‐Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light‐Emitting Diodes

Cited by 34 publications

References 44 publications

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts

Thermally Activated Delayed Fluorescence (Green) in Undoped Film and Exciplex Emission (Blue) in Acridone–Carbazole Derivatives for OLEDs

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