Dihedral Angle Control of Blue Thermally Activated Delayed Fluorescent Emitters through Donor Substitution Position for Efficient Reverse Intersystem Crossing

Oh, Chahyun; Pereira, Daniel de Sa; Han, Si Hyun; Park, Hee-Jun; Higginbotham, Heather F.; Monkman, Andrew P.; Lee, Jun Yeob

doi:10.1021/acsami.8b10595

Cited by 78 publications

(66 citation statements)

References 37 publications

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“…Unexpectedly, the phosphorescence spectrum of TRZ‐ m ‐ACRSA slightly blueshifts from its steady‐state PL spectrum at 77 K, exhibiting a negative

Δ E_{{false(}^{1} CT -^{3} CT)}

. Similar phenomenon was observed from numbers of TRZ based materials with meta‐position configuration, including TRZ‐ m ‐ACR (Figure S11, Supporting Information), and specific exciplex . Most interestingly, the phosphorescence spectra of TRZ‐ m ‐ACRSA and TRZ‐ m ‐ACR are almost identical while they have different steady‐state PL spectra at 77 K. In general, according to Hund's rule, 1 CT should have higher energy levels than 3 CT when 1 CT and 3 CT are describing the same CT state.…”

Section: Resultssupporting

confidence: 61%

Utilizing a Spiro TADF Moiety as a Functional Electron Donor in TADF Molecular Design toward Efficient “Multichannel” Reverse Intersystem Crossing

Gan

Wang

et al. 2019

Adv Funct Materials

111

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Designing thermally activated delayed fluorescence (TADF) materials with an efficient reverse intersystem crossing (RISC) process is regarded as the key to actualize efficient organic light-emitting diodes (OLEDs) with low efficiency roll-off. Herein, a novel molecular design strategy is reported where a typical TADF material 10-phenyl-10H, 10′H-spiro[acridine-9, 9′-anthracen]-10′-one (ACRSA) is utilized as a functional electron donor to design TADF materials of 2,4,6-triphenyl-1,3,5-triazine(TRZ)-p-ACRSA and TRZ-m-ACRSA. It is unique that the intramolecular charge transfer of the ACRSA moiety and the intramolecular and through-space intermolecular charge transfer between the TRZ and ACRSA moieties, provide a "multichannel" effect to enhance the rate of the reverse intersystem crossing process (k risc ) exceeding 10 −6 s −1 . TADF OLEDs based on TRZ-p-ACRSA as an emitter show a maximum external quantum efficiency (EQE) of 28% with reduced efficiency roll-off (EQEs of 27.5% and 22.1% at 100 and 1000 cd m −2 , respectively). Yellow phosphorescent OLEDs utilizing TRZ-p-ACRSA as a host material show record-high EQE of 25.5% and power efficiency of 115 lm W −1 , while phosphorescent OLEDs based on TRZ-m-ACRSA show further lower efficiency roll-off with EQEs of 25.2%, 24.3%, and 21.5% at 100, 1000, and 10 000 cd m −2 , respectively.being consistent with the El-Sayed rule of intersystem crossing (ISC) process, when the natures of 1 CT and 3 CT are different, the SOC between 1 CT and 3 CT might be efficient as well. [2] More importantly, avoiding dual emission phenomenon, which caused by conformational transforming brought by flexible moieties, is considered as the first priority of TADF molecular design strategy. [9] Conformational transforming not only results in energy loss, but also limits the triplet exciton utilization because not all possible conformations have potential to achieve TADF phenomenon. [10] On the basis of this understanding, the key to design TADF

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“…Unexpectedly, the phosphorescence spectrum of TRZ‐ m ‐ACRSA slightly blueshifts from its steady‐state PL spectrum at 77 K, exhibiting a negative

Δ E_{{false(}^{1} CT -^{3} CT)}

Section: Resultssupporting

confidence: 61%

Utilizing a Spiro TADF Moiety as a Functional Electron Donor in TADF Molecular Design toward Efficient “Multichannel” Reverse Intersystem Crossing

Gan

Wang

et al. 2019

Adv Funct Materials

111

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“…10−12 The rISC mechanism in these TADF emitters is a second-order spinvibronic coupling between a local-excited triplet state ( 3 LE) and a charge-transfer triplet state ( 3 CT) which mediates spin−orbit coupling to the CT singlet state ( 1 CT) leading to emission. 13,14 In this case the 3 LE state acts as a mediator state for the spin flip.…”

Section: ■ Introductionmentioning

confidence: 99%

Bond Rotations and Heteroatom Effects in Donor–Acceptor–Donor Molecules: Implications for Thermally Activated Delayed Fluorescence and Room Temperature Phosphorescence

et al. 2018

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New thermally activated delayed fluorescence (TADF) blue emitter molecules based on the known donor−acceptor−donor (D−A−D)type TADF molecule, 2,7-bis(9,9-dimethylacridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2), are reported. The motivation for the present investigation is via the use of rational molecular design, based on DDMA-TXO2, to elevate the organic light emitting diode (OLED) performance and obtain deeper blue color coordinates. To achieve this goal, the strength of the donor (D) unit and acceptor (A) units have been tuned with methyl substituents. The methyl functionality on the acceptor was also expected to modulate the D−A torsion angle in order to obtain a blue shift in the electroluminescence. The effect of regioisomeric structures has also been investigated. Herein, we report the photophysical, electrochemical, and single-crystal X-ray crystallography data to assist with the successful OLED design. The methyl substituents on the DDMA-TXO2 framework have profound effects on the photophysics and color coordinates of the emitters. The weak electron-donating methyl groups alter the redox properties of the D and A units and consequently affect the singlet and triplet levels but not the energy gap (ΔE ST ). By systematically manipulating all of the aforementioned factors, devices have been obtained with acceptor-substituted III with a maximum external quantum efficiency of 22.6% and Commission Internationale de l'Ećlairage coordinates of (0.15, 0.18) at 1000 cd m −2 .

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“…The substitution site of donor units can influence the conjugation, the spatial separation of the HOMO and LUMO and oscillator strength ( f ), although more donor units can be introduced in TADF emitters . Thus, the conformational and region‐isomerism of the TADF emitters can greatly impact photophysical properties of these emitters and ultimately the device performance . Especially, the pheno‐thiazine (PTZ) donor exhibit two heterogenous conformers with stoutly different electronic and optical properties .…”

Section: Introductionmentioning

confidence: 99%

Substitution Conformation Balances the Oscillator Strength and Singlet–Triplet Energy Gap for Highly Efficient D–A–D Thermally Activated Delayed Fluorescence Emitters

Wei

et al. 2019

Advanced Optical Materials

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Four donor-acceptor-donor region isomers (2,3-TXO-PhCz, 2,6-TXO-PhCz, 2,7-TXO-PhCz, and 3,6-TXO-PhCz) are designed. The substitution positions of the two PhCz units significantly impact the photophysical properties of the isomers, especially for the singlet-triplet energy splitting (ΔE ST ) and oscillator strength (f ). 2,3-TXO-PhCz exhibits weak emission due to the large steric hindrance of the two PhCz units. While 2,6-TXO-PhCz, 2,7-TXO-PhCz, and 3,6-TXO-PhCz all exhibit strong emission. The four emitters possess small ΔE ST of 0.01-0.24 eV; the corresponding f values are 0.064, 0.107, 0.026, and 0.134. Consequently, the photoluminescence quantum yields (PLQYs) of the doped films in CBP host are: 62.1% for 2,3-TXO-PhCz, 83.8% for 2,6-TXO-PhCz, 89.0% for 2,7-TXO-PhCz, and 85.4% for 3,6-TXO-PhCz. Although notable divergences of f and ΔE ST exist between 2,6-TXO-PhCz and 2,7-TXO-PhCz, similar PLQY of doped film in the CBP host, and exciton utilization and external quantum efficiency (EQE) of the corresponding devices can be achieved: 2,6-TXO-PhCz and 2,7-TXO-PhCz endow the organic lightemitting devices with high EQE of 23.2% and 24.4%. This proximity can be attributed to the synergistic effect of f and ΔE ST . This finding highlights the beneficial role of the different linking positions on the acceptor unit in facilitating the adjustment of f and ΔE ST in order to improve the device efficiency.

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Dihedral Angle Control of Blue Thermally Activated Delayed Fluorescent Emitters through Donor Substitution Position for Efficient Reverse Intersystem Crossing

Cited by 78 publications

References 37 publications

Utilizing a Spiro TADF Moiety as a Functional Electron Donor in TADF Molecular Design toward Efficient “Multichannel” Reverse Intersystem Crossing

Utilizing a Spiro TADF Moiety as a Functional Electron Donor in TADF Molecular Design toward Efficient “Multichannel” Reverse Intersystem Crossing

Bond Rotations and Heteroatom Effects in Donor–Acceptor–Donor Molecules: Implications for Thermally Activated Delayed Fluorescence and Room Temperature Phosphorescence

Substitution Conformation Balances the Oscillator Strength and Singlet–Triplet Energy Gap for Highly Efficient D–A–D Thermally Activated Delayed Fluorescence Emitters

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