Toward an Accurate Description of Thermally Activated Delayed Fluorescence: Equal Importance of Electronic and Geometric Factors

Wang, Chao; Zhou, Keren; Huang, Shuping; Zhang, Qisheng

doi:10.1021/acs.jpcc.9b01896

Cited by 14 publications

(9 citation statements)

References 69 publications

(118 reference statements)

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“…However, some disadvantages such as expensive material cost and short lifetime hinder the extension of phosphorescent materials. − After the pioneering research by Adachi et al, thermally activated delayed fluorescence (TADF) material has drawn great attraction in recent years, which show potential as an interesting low-cost alternative to phosphorescent materials. , The TADF emitters can reach 100% IQE by converting all singlet and triplet excitons into photons via the reverse intersystem crossing (RISC) process from the lowest triplet excited state (T 1 ) to singlet excited state (S 1 ). − A sufficiently small S 1 –T 1 energy split (Δ E ST ) is necessary for the efficient RISC process . Generally, such a small Δ E ST can be achieved by constructing a twisted donor–acceptor structure with adequate separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). , …”

Section: Introductionmentioning

confidence: 99%

Rational Molecular Design of Dibenzo[a,c]phenazine-Based Thermally Activated Delayed Fluorescence Emitters for Orange-Red OLEDs with EQE up to 22.0%

Xie

Dai

et al. 2019

ACS Appl. Mater. Interfaces

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The design and synthesis of highly efficient thermally activated delayed fluorescence (TADF) emitters with an electroluminescence wavelength beyond 600 nm remains a great challenge for organic light-emitting diodes (OLEDs). To solve this issue, three TADF molecules, xDMAC−BP (x = 1, 2, 3), are developed in combination with the rigid planar dibenzo[a,c]phenazine (BP) acceptor core and different numbers of 9,9dimethylacridan (DMAC) donors. All these emitters possess stable internal charge transfer and a large dihedral angle between the donors and planar BP core. The emission wavelength can be regulated from 541 to 605 nm by increasing the number of the donor DMAC units because of the controllable tuning of the intramolecular charge transfer effect and the molecular geometrical structure. The photoluminescence quantum yields of these emitters are improved from 42 to 89% with the increase in the number of DMAC units. The orange-red OLEDs employing the xDMAC−BP emitters exhibit maximum external quantum efficiency (EQE) of 22.0% at 606 nm, which is the highest EQE of the previously reported TADF OLEDs exceeding 600 nm.

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Section: Introductionmentioning

confidence: 99%

Rational Molecular Design of Dibenzo[a,c]phenazine-Based Thermally Activated Delayed Fluorescence Emitters for Orange-Red OLEDs with EQE up to 22.0%

Xie

Dai

et al. 2019

ACS Appl. Mater. Interfaces

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“…In addition, the thermally activated delayed fluorescence (TADF) molecules applied in efficient OLEDs are mainly ICT molecules. , Pure organic TADF emitters have recently become a research hotspot because of their potential application in OLEDs. − A typical molecular scheme to achieve TADF usually consists of D and A moieties (D–A system) that can form intramolecular CT states with a very small singlet–triplet energy gap (Δ E ST ) between the lowest triplet state (T 1 ) and the lowest excited singlet state (S 1 ), and thermal energy can induce reverse intersystem crossing (rISC) from the T 1 to the S 1 state. , …”

Section: Introductionmentioning

confidence: 99%

Regulation of the Molecular Architectures on Second-Order Nonlinear Optical Response and Thermally Activated Delayed Fluorescence Property: Homoconjugation and Twisted Donor–Acceptor

Wang

Zhang

et al. 2019

J. Phys. Chem. C

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The nonlinear optical (NLO) and thermally activated delayed fluorescence (TADF) properties of organic push–pull materials consisting of π-conjugated electron-donating (D) and electron-accepting (A) subunits are dominated by the interaction of D and A moieties via intramolecular charge transfer (ICT). Understanding the structure–property relationship, at the microscopic level, is the prerequisite for further performance optimization or improvement. In this work, we theoretically investigated the geometric and electronic structures, CT properties, polarizabilities (α), first hyperpolarizabilities (βtot), and singlet–triplet energy gap (ΔE ST) of the homoconjugation (as type I) and the conventional conjugation D–A (as type II) compounds. A noteworthy finding was that the type II molecule was suggested to promote the performance in NLO due to the lower excited energy and larger dipole moment variations for the crucial excited state, as well as the larger separate distributions of first hyperpolarizability density. In addition, the electron transition properties, second-order NLO responses, and ΔE ST values strongly depend on the nature of different electron acceptors (pyrazine → dicyanopyrazine → dicyanoquinoxaline). Further, based on the polarizable continuum model analysis, the increment in the βtot of all studied compounds is preferable for NLO applications. Moreover, the ΔE ST values of the molecules in which the acceptor are replaced by dicyanopyrazine/dicyanoquinoxaline (2, 3, and 6) in vacuum are reduced by an order of magnitude when embedded in a polarizable environment, indicating they are potentially efficient TADF materials. Overall, we envision that the various architectures and the polarization effect introduced in the present work will offer a route toward the rational design of such kind of D–A system for novel functional second-order NLO and TADF materials.

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“…The computed Δ E ST value of complex 2 is 1394 cm –1 , which is in agreement with the experimental value of 1195 cm –1 , while for complex 1 , because of its poor rigidity and the absence of a monocrystalline structure, the calculated Δ E ST value (1422 cm –1 ) in solution deviates somewhat from the experimentally measured value (741 cm –1 ) in solid. Also, more accurate calculation of the excited-state properties is the focus of our future research. − From eq , it is easy to find that Δ E ST and λ have an important impact on k ISC and k RISC , and their relationship can be determined from eqs and : , …”

Section: Resultsmentioning

confidence: 99%

Molecular-Level Insight of Cu(I) Complexes with the 7,8-Bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate Ligand as a Thermally Activated Delayed Fluorescence Emitter: Luminescent Mechanism and Design Strategy

Ren

Chen

et al. 2020

Inorg. Chem.

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Investigation of the clear structure−property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction worthy of continuous efforts. The instructive theoretical principle of TADF material design is critical and challenging. Here, we carried out theoretical calculation on two experimental Cu(I) complexes with the same 7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate (dppnc) but different N^N ligands [dmbpy = 6,6′-dimethyl-2,2′-bipyridine (1) or dmp = 2,9dimethyl-1,10-phenanthroline (2)] to briefly elaborate the structure−TADF performance relationship and luminescence mechanism. It was found that enhanced rigidity by the fused benzene ring between two pyridyl units in complex 2 leads to (i) higher allowedness of S 1 → S 0 , (ii) more effective reverse intersystem crossing (RISC), and (iii) better relative stability of the T 1 state, which could be responsible for its excellent TADF behavior. Thus, a strategy of extending π conjugation in the N^N ligand could be deduced to further enhance the quantum yield. We validated it and have succeeded in designing analogue complex 4 by extending π conjugation with an electron-withdrawing pyrazinyl. Benefiting from the smaller energy gap (ΔE ST ) and plunged reorganization energy between the S 1 and T 1 states, the rate of RISC in complex 4 (1.05 × 10 8 s −1 ) increased 2 orders of magnitude relative to that of 2 (5.80 × 10 6 s −1 ), showing more superiority of the TADF behavior through a better balance of RISC, fluorescence, and phosphorescence decay. Meanwhile, the thermally activated temperature of 4 is only 165 K, implying that there is a low-energy barrier. All of these indicate that the designed complex 4 may be a potential TADF candidate.

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Toward an Accurate Description of Thermally Activated Delayed Fluorescence: Equal Importance of Electronic and Geometric Factors

Cited by 14 publications

References 69 publications

Rational Molecular Design of Dibenzo[a,c]phenazine-Based Thermally Activated Delayed Fluorescence Emitters for Orange-Red OLEDs with EQE up to 22.0%

Rational Molecular Design of Dibenzo[a,c]phenazine-Based Thermally Activated Delayed Fluorescence Emitters for Orange-Red OLEDs with EQE up to 22.0%

Regulation of the Molecular Architectures on Second-Order Nonlinear Optical Response and Thermally Activated Delayed Fluorescence Property: Homoconjugation and Twisted Donor–Acceptor

Molecular-Level Insight of Cu(I) Complexes with the 7,8-Bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate Ligand as a Thermally Activated Delayed Fluorescence Emitter: Luminescent Mechanism and Design Strategy

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