Contributions of a Higher Triplet Excited State to the Emission Properties of a Thermally Activated Delayed-Fluorescence Emitter

Kobayashi, Takashi; Niwa, Akitsugu; Takaki, Kensho; Haseyama, Shota; Nagase, Takashi; Goushi, Kenichi; Adachi, Chihaya; Naito, Hiroyoshi

doi:10.1103/physrevapplied.7.034002

Cited by 52 publications

(62 citation statements)

References 22 publications

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“…In this work, we have derived some relations for the determination of k ISC based on the three‐level model. These relations can be easily expanded to the four‐level system in which T n is considered, and almost the same relations will be obtained. The only difference is that the calculated value is the sum of two ISC rates from S 1 into T 1 and T n in the four‐level system, although that between S 1 and T 1 must be much smaller.…”

Section: Discussionmentioning

confidence: 75%

Intersystem Crossing Rate in Thermally Activated Delayed Fluorescence Emitters

Kobayashi

Kawate

Niwa

et al. 2019

Physica Status Solidi (a)

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For a better understanding of the exciton decay process in thermally activated delayed fluorescence (TADF) emitters, the intersystem crossing rate, k ISC , is one of the important physical constants that have to be determined. Herein, a method to calculate the k ISC value from photoluminescence (PL) measurements is reconsidered. The k ISC value can be determined at very low temperatures where delayed fluorescence (DF) is completely suppressed, as well as around room temperature where triplet excitons mainly decay into the ground state by emitting DF. However, there is a temperature range where the k ISC value cannot be determined accurately because the influences of nonradiative decay paths can be neither ignored nor corrected. For such a temperature range, an alternative approach, which utilizes the temperature dependence of an observed PL decay rate, is presented. In this way, k ISC values from 300 to 10 K are determined for thin films of two TADF emitters, i.e., 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene, which are known as 4CzIPN and 2CzPN, respectively.

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Section: Discussionmentioning

confidence: 75%

Intersystem Crossing Rate in Thermally Activated Delayed Fluorescence Emitters

Kobayashi

Kawate

Niwa

et al. 2019

Physica Status Solidi (a)

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“…SSSE have been shown to be especially important in 3 rd generation OLEDs exploiting TADF 17,37,38,[53][54][55][56][57][58] . The origin of this derives from recent work demonstrating that TADF is not simply a cyclic process between the singlet and triplet CT manifolds, but involves coupling to other states 12,38,40,42,47,59,60 , such as local triplet ππ * ( 3 LE) 12 or nπ * states 40 . The effectiveness of the mixing between the states and therefore of the overall TADF process crucially depends energy gap between them.…”

Section: The Environment Effectmentioning

confidence: 99%

The theory of thermally activated delayed fluorescence for organic light emitting diodes

2018

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The interest in organic molecules exhibiting thermally activated delayed fluorescence (TADF) has been reinvigorated in recent years owing to their potential to be exploited as emitters in highly efficient purely organic light emitting diodes (OLEDs). However, designing new molecules that exhibit efficient TADF is a non-trivial task because they would appear to require the optimisation of a number of contrasting properties. For example these molecules must exhibit rapid conversion between the singlet and triplet manifolds without the use of heavy elements to enhance spin-orbit coupling. They should also display a large fluorescence rate, but simultaneously a small energy gap between low lying singlet and triplet states. Consequently to achieve systematic material design, a detailed understanding of the fundamental factors influencing the photophysical behaviour of TADF emitters is essential. Towards achieving this goal, theory and computation is playing a crucial role. In this feature article the recent progress in the theory of organic TADF molecules in the context of OLEDs is presented, with a view of achieving a deeper understanding of these molecules and driving systematic material design.

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“…This is consistent with recent findings where considering T n , as well as S 1 , T 1 and S 0 is essential to understand the exciton decay dynamics in TADF emitters. 12,16 It is also important to highlight that this effect is not correlated with the charge transfer character of the singlet and triplet states. Fig.…”

Section: View Article Onlinementioning

confidence: 99%

“…10,11 Detailed investigations aimed at revealing the fundamental mechanisms of TADF and RTP are also topics of strong research focus, because they offer excellent opportunities to investigate the dynamics of excited triplet states in organic materials. 12 These studies can, therefore, provide valuable information about the role of molecular conformation and connectivity, and coupling between electronic states for promoting triplet harvesting. These aspects are still not completely understood, and are extremely relevant when the properties of the triplet excited state are of importance, such as in photon up-conversion due to triplettriplet annihilation, 13 triplet harvesting in OLEDs, [14][15][16] and organic spintronics.…”

Section: Introductionmentioning

confidence: 99%