Engineering the singlet–triplet energy splitting in a TADF molecule

Abstract

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 .

Using Guest–Host Interactions To Optimize the Efficiency of TADF OLEDs

“…[4][5][6][7][8][9] One way to improve the TADF emission contribution is to minimize the energy splitting (∆E ST ) between singlet and triplet states. Recent experimental studies [10][11][12] along with initial theoretical work [13][14][15] identify that the SOC mechanism in these TADF systems is a complex second order process requiring vibronic coupling between 3 CT and 3 LE to mediate the spin flip back to the 1 CT state, the 3 LE state mediates the SOC between the singlet and triplet CT states 15 . Hence whereas the CT states are very sensitive to the local enviroment 10 the local triplet states are not, therefore the host differential effects the energy gaps which directly changes the rate of reverse intersystem crossing (rISC).…”

Dynamic nature of excited states of donor–acceptor TADF materials for OLEDs: how theory can reveal structure–property relationships

“…This appears to be a consequence of a larger 3 LE-1 CT spin-orbit coupling in comparison to the 3 CT -1 CT one, because of the different spatial localization of the involved states. [17][18][19] As an alternative to these mechanisms driven by spin-orbit coupling, interconversion driven by hyperfine couplings has also been reported but appears to be a negligible pathway since its contribution requires an energy spacing between the 3 CT and 1 CT…”

Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

“…4, the vast majority of all published organic TADF emitters contain substituted carbazole- [56][57][58][59] or arylamine-type donors. [60][61][62] In most cases, the connection to the acceptors is realized via the aromatic nitrogen. On the acceptor-side (Fig.…”

“…5), one can find a plethora of nitrogen-containing heterocycles, 63,64 as well as various benzonitriles. [47][48][49]56,57,59,65,66 A third acceptor-class is sulfones, 31,54,58,60,67,68 which seems to be particularly useful to realize deep-blue TADF emission.…”