Nature of Highly Efficient Thermally Activated Delayed Fluorescence in Organic Light-Emitting Diode Emitters: Nonadiabatic Effect between Excited States

Chen, Xiankai; Zhang, Shou Feng; Fan, Jian Xun; Ren, Ai Min

doi:10.1021/acs.jpcc.5b00276

Cited by 216 publications

(212 citation statements)

References 26 publications

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“…However, our recent experimental19 and quantum dynamics studies20 suggest that the intersystem crossing (ISC) and reverse intersystem crossing (rISC) between 1 CT singlet and 3 CT triplet states is a more complicated second order process. This second order process is mediated by vibronic coupling of the 3 CT to the local exciton triplet ( 3 LE) states to allow spin–orbit coupling to the 1 CT state182021. These results are also in line with the previous findings of Lim et al 22.…”

supporting

confidence: 88%

Revealing the spin–vibronic coupling mechanism of thermally activated delayed fluorescence

et al. 2016

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Knowing the underlying photophysics of thermally activated delayed fluorescence (TADF) allows proper design of high efficiency organic light-emitting diodes. We have proposed a model to describe reverse intersystem crossing (rISC) in donor–acceptor charge transfer molecules, where spin–orbit coupling between singlet and triplet states is mediated by one of the local triplet states of the donor (or acceptor). This second order, vibronically coupled mechanism describes the basic photophysics of TADF. Through a series of measurements, whereby the energy ordering of the charge transfer (CT) excited states and the local triplet are tuned in and out of resonance, we show that TADF reaches a maximum at the resonance point, substantiating our model of rISC. Moreover, using photoinduced absorption, we show how the populations of both singlet and triplet CT states and the local triplet state change in and out of resonance. Our vibronic coupling rISC model is used to predict this behaviour and describes how rISC and TADF are affected by external perturbation.

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supporting

confidence: 88%

Revealing the spin–vibronic coupling mechanism of thermally activated delayed fluorescence

et al. 2016

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“…58 The former plays an important role in determining the rate of ISC and rISC. Given the presence of only light elements this can be expected to be only a small perturbation, it is important that a non-zero value is obtained, even if the energy gap between the states is small.…”

Section: Discussionmentioning

confidence: 99%

On Predicting the Excited-State Properties of Thermally Activated Delayed Fluorescence Emitters

2015

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Limitations imposed by spin statistics governing exciton formation has meant that most efficient organic light emitting diodes (OLEDs) have relied upon complexes containing heavy metals. This can be overcome by exploiting thermally activated delayed fluorescence (TADF), which has opened the opportunity to design emitters composed only of lighter more abundant elements. For these complexes charge transfer excitations play a central role, meaning that modelling their properties within the framework of time-dependent density functional theory (TD-DFT) is challenging. Herein, two computational approaches to rectify this are explored. Firstly, an analysis based on the overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). This qualitative approach provides a satisfactory and very computationally efficient prediction of the energy gap between the lowest singlet and triplet excited states, crucial for TADF. In the second approach, the excited state properties are explicitly calculated using TD-DFT, by optimising the rangeseparation parameter within range-corrected functionals. This yields quantitative agreement with experimental results and can therefore be used to rationalise the photophysical properties of these complexes.

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“…The subsequent results show that D-A-D displays more efficient TADF, and higher photoluminescence quantum yields (PLQY) versus their analogues D-A. 16,17 For this reason, we have synthesised the 2,7-bis(phenoxazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPO-TXO2), a D-A-D TADF emitter formed by phenoxazine (D) donors and the 9,9-dimethylthioxanthene-S,S-dioxide (TXO2) (A) acceptor. Phenoxazine was chosen because of its strong electron donor character, due its low ionization potential, and because it assumes a near D-A orthogonal structure.…”

Section: Introductionmentioning

confidence: 93%

Engineering the singlet–triplet energy splitting in a TADF molecule

et al. 2016

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The key to engineering an efficient TADF emitter is to achieve a small energy splitting between a pair of molecular singlet and triplet states. This work makes important contributions towards achieving this goal. By studying the new TADF emitter 2,7-bis(phenoxazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPO-TXO2) and the donor and acceptor units separately, the available radiative and non-radiative pathways of DPO-TXO2 have been identified. The energy splitting between singlet and triplet states was clearly identified in four different environments, in solutions and solid state. The results show that DPO-TXO2 is a promising TADF emitter, having ∆EST = 0.01 eV in zeonex matrix. We further show how the environment plays a key role in the fine tuning of the energy levels of the 1 CT state with respect to the donor 3 LED triplet state, which can then be used to control the ∆EST energy value. We elucidate the TADF mechanism dynamics when the 1 CT state is located below the 3 LE triplet state which it spin orbit couples to, and we also discuss the OLED device performance with this new emitter, which shows maximum external quantum efficiency (E.Q.E) of 13.5% at 166 cd/m 2 .

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Nature of Highly Efficient Thermally Activated Delayed Fluorescence in Organic Light-Emitting Diode Emitters: Nonadiabatic Effect between Excited States

Cited by 216 publications

References 26 publications

Revealing the spin–vibronic coupling mechanism of thermally activated delayed fluorescence

Revealing the spin–vibronic coupling mechanism of thermally activated delayed fluorescence

On Predicting the Excited-State Properties of Thermally Activated Delayed Fluorescence Emitters

Engineering the singlet–triplet energy splitting in a TADF molecule

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