Suppression of Concentration Quenching in Ortho‐Substituted Thermally Activated Delayed Fluorescence Emitters

Abroshan, Hadi; Cho, Eunkyung; Coropceanu, Veaceslav; Brédas, Jean‐Luc

doi:10.1002/adts.201900185

Cited by 21 publications

(28 citation statements)

References 111 publications

(144 reference statements)

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“…[ 46 ] An approximately linear correlation is found between the V SOC and Δ E ST values ( V SOC ∝ Δ E ST , Figure 8c), which is consistent with results reported for other TADF molecules. [ 47,48 ] This relation indicates that, at least on average, a decrease in Δ E ST simultaneously lowers V SOC between the S 1 and T 1 states. While a decrease in Δ E ST increases k RISC , a reduction in V SOC has the opposite effect.…”

Section: Resultsmentioning

confidence: 99%

“…Interestingly, while the distribution of the k r values follows a Gaussian evolution in TPBe, the radiative decay rate distribution in the 4CzDPO molecules has an exponential shape ( Figure ); we recently reported a similar feature for another TADF molecule, oBFCzTrz (5‐(2‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐5 H ‐benzofuro[3,2‐ c ]carbazole). [ 48 ] Further investigations are required to understand the underlying reason for the differences in the k r distributions in traditional fluorescent emitters such as TPBe and in TADF molecules, and the relevance of these differences in the operation of the optoelectronic devices.…”

Section: Resultsmentioning

confidence: 99%

“…Recent studies have shown that this type of linkage disfavors intermolecular π-π stacking among TADF molecules, and simultaneously enhances spinorbit couplings between the S 1 and T 1 states. [48,51,52] These molecular features of ortho-linked donor/acceptor TADF molecules can help not only improve the rates of RISC processes for fast singlet-exciton generation in TADF molecules, but also suppress the formation of intermolecular aggregate states as well as the need for a host material, which all can improve IQEs in hyperfluorescence-based devices. Excitation energy-transfer calculations show that the Förster mechanism leads to efficient energy transfer from 4CzDPO to TBPe.…”

Section: Discussionmentioning

confidence: 99%

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Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

Abroshan

Zhang

et al. 2020

Adv Funct Materials

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Hyperfluorescence is emerging as a powerful strategy to develop optoelectronic devices with high-color purity and enhanced stability. It requires appropriate integration of a sensitizer displaying efficient thermally activated delayed fluorescence (TADF) and an emitter displaying strong, narrowband fluorescence. Here, through a joint computational and experimental approach, an unprecedented, end-to-end systems level description of the electronic and optical processes that take place in a hyperfluorescent emissive layer composed of a TADF sensitizer, 2,5-bis(2,6-di(9H-carbazol-9-yl) phenyl)-1,3,4-oxadiazole (4CzDPO), and a fluorescent emitter, 2,5,8,11-tetratert-butylperylene (TBPe) is provided. The photophysical properties measurement of the emissive layer is combined with the computational determination of the electronic properties, film morphology, and excitation transfer phenomena. The Förster resonance energy transfer rates from 4CzDPO to TBPe are on the order of 10 11 s −1 , considerably higher than the radiative and nonradiative recombination rates for 4CzDPO. These features ensure nearly complete energy transfer to TBPe, leading to a five-fold increase in the photoluminescence quantum yields in the 4CzDPO:TBPe system in comparison to neat films of 4CzDPO. This approach highlights the factors that can provide efficient energy transfer from TADF molecules to fluorescent emitters, suppress energy transfer among TADF molecules, and avoid the need for a host material within the emissive layer.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

Abroshan

Zhang

et al. 2020

Adv Funct Materials

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“…We note, however, that some TADF emitters show insignificant concentration quenching dependence. [ 24,26–28 ]…”

Section: Introductionmentioning

confidence: 99%

The Role of Intermolecular Interactions on the Performance of Organic Thermally Activated Delayed Fluorescence (TADF) Materials

Cho

Hong²,

Coropceanu

et al. 2021

Advanced Optical Materials

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In most instances, thermally activated delayed fluorescence (TADF) emitters are incorporated into a suitable host matrix at low doping concentration in order to reduce emission quenching and to improve organic light‐emitting diode (OLED) efficiency. Here, a combination of molecular dynamics simulations and density functional theory calculations is performed for thin films of 1) the neat 4CzIPN TADF emitter and 2) the (guest–host) 4CzIPN:mCBP system, in order to determine how guest–guest and guest–host interactions influence the morphological, electronic, and luminescence properties of the TADF emitters. The red‐shift in emission recently observed experimentally upon increasing the concentration in TADF emitters is attributed to the formation of guest–guest, i.e., dimer, intermolecular charge‐transfer states. It is found that the radiative and reverse intersystem crossing rates associated with these dimer states are similar to those of monomers. Thus, the contributions from both the dimer and monomer states need to be considered to describe TADF within the emissive layer. The exciton diffusion processes are also characterized; singlet excitons are calculated to be the main contributors to the diffusion length, in contrast to recently proposed models.

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“…Two proven approaches are based on the use of i) heavy metal‐based phosphors (which are the emitters currently used in commercial OLEDs), where large spin–orbit couplings facilitate radiative transitions from T 1 to the ground state (S 0 ) [ 6–10 ] and ii) purely organic thermally activated delayed fluorescence (TADF) emitters, where T 1 excitons can up convert into S 1 excitons that subsequently decay radiatively. [ 11–19 ]…”

Section: Introductionmentioning

confidence: 99%

Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

Abroshan

Coropceanu

Brédas

2020

Adv Funct Materials

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Radical‐carrying organic molecules have received significant attention to bypass the issue related to harvesting triplet excitons in current light‐emitting materials. While the computational efforts conducted so far have treated these radical emitters as isolated entities, in actual devices, they are embedded in a host matrix and subject to emitter–host interactions. Here, by combining molecular dynamics simulations and density functional theory calculations, the impact of the host matrix on the optoelectronic performance of radical emitters is evaluated, taking as a representative example the (4‐ncarbazolyl‐2,6‐dichlorophenyl)bis(2,4,6‐trichlorophenyl)‐methyl (TTM‐3NCz) radical emitter dispersed in a 4,4‐bis(carbazol‐9‐yl)biphenyl (CBP) host. A morphological analysis shows that steric effects around the radical centers, carried by the TTM electron‐poor moieties of the emitters, disfavor π–π interactions with the host molecules, which leads to random intermolecular orientations around the TTM moieties. The 3NCz electron‐rich moieties of the emitters, however, have much lesser spatial hindrance for intermolecular π–π stacking, which modulates the structural and electronic properties of the emitters in the host matrix. The influence of dynamic and static disorders on the radiative and nonradiative recombination processes is also investigated and it is found that the rates of nonradiative recombination are small, which opens the way to 100% internal quantum efficiency for the doublet‐based emission process.

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Suppression of Concentration Quenching in Ortho‐Substituted Thermally Activated Delayed Fluorescence Emitters

Cited by 21 publications

References 111 publications

Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

The Role of Intermolecular Interactions on the Performance of Organic Thermally Activated Delayed Fluorescence (TADF) Materials

Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

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