Direct Observation of Spin States Involved in Organic Electroluminescence Based on Thermally Activated Delayed Fluorescence

Väth, Stefan; Tvingstedt, Kristofer; Auth, Michael; Sperlich, Andreas; Dabulienė, Asta; Gražulevičius, Juozas V.; Stakhira, Pavlo; Cherpak, Vladyslav; Dyakonov, Vladimir

doi:10.1002/adom.201600926

Cited by 11 publications

(10 citation statements)

References 27 publications

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“…Hence, it is not unexpected that OPV CT states exhibit very low EL quantum efficiency in the order of 10 −6 ( 80 ). We conclude that the m-MTDATA:BPhen exciplex emitter with D = 50 ± 5 MHz and a singlet-triplet gap of ∆ E ST = 58 meV ( 24 , 25 ) is an intermediate case, between highly emissive intramolecular TADF and poorly emissive OPV CT states, revealing large or nearly zero dipolar interactions, respectively.…”

Section: Discussionmentioning

confidence: 83%

“…The strength of the effect is evaluated by the ELDMR contrast ∆EL/EL. A detailed description of ELDMR can be found in previous publications ( 24 , 25 ), where also the singlet-triplet energy gap ∆ E ST = 58 meV was estimated for the MTDATA:BPhen blends, which is, by far, the largest energy contribution among the spin-spin interaction terms in Eq. 1 .…”

Section: Resultsmentioning

confidence: 99%

“…In a spin-resonance experiment, microwaves with a properly chosen energy (frequency) flip the spin orientation and connect the m s = ±1 and m s = 0 substates of a triplet exciplex, which, in turn, facilitates population transfer to an emissive singlet exciplex final state. However, the underlying spin physics is quite complex as the spin-spin interactions in such electron-hole pairs depend strongly on the molecular environment, as well as on the details of how these excited states are created, e.g., optically excited or by injection from electrodes ( 24 , 25 ). Furthermore, the strength of the spin-spin interaction determines the energy gap between the states m s = 0 and m s = ±1, the so-called zero-field splitting (ZFS), and in practice is given by the spatial distance.…”

Section: Introductionmentioning

confidence: 99%

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Long-lived spin-polarized intermolecular exciplex states in thermally activated delayed fluorescence-based organic light-emitting diodes

et al. 2021

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Section: Discussionmentioning

confidence: 83%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Long-lived spin-polarized intermolecular exciplex states in thermally activated delayed fluorescence-based organic light-emitting diodes

et al. 2021

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“…These measurements elucidate properties of triplet states which are involved in the light generation mechanisms of the devices and the temperature dependence reveals the TADF activation energy. [ 19,22 ] The idea of ELDMR experiments is to probe EL, while applying a static magnetic field B that induces a Zeeman splitting of triplet states. By applying resonant microwaves, the following resonance condition is fulfilled.…”

Section: Magnetic Resonancementioning

confidence: 99%

Spin‐ and Voltage‐Dependent Emission from Intra‐ and Intermolecular TADF OLEDs

Bunzmann

Krugmann

Weissenseel

et al. 2021

Adv Elect Materials

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Organic light emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) utilize molecular systems with a small energy splitting between singlet and triplet states. This can either be realized in intramolecular charge transfer states of molecules with near‐orthogonal donor and acceptor moieties or in intermolecular exciplex states formed between a suitable combination of individual donor and acceptor materials. Here, 4,4′‐(9H,9′H‐[3,3′‐bicarbazole]‐9,9′‐diyl)bis(3‐(trifluoromethyl) benzonitrile) (pCNBCzoCF3) is investigated, which shows intramolecular TADF but can also form exciplex states in combination with 4,4′,4′′‐tris[phenyl(m‐tolyl)amino]triphenylamine (m‐MTDATA). Orange emitting exciplex‐based OLEDs additionally generate a sky‐blue emission from the intramolecular emitter with an intensity that can be voltage‐controlled. Electroluminescence detected magnetic resonance (ELDMR) is applied to study the thermally activated spin‐dependent triplet to singlet up‐conversion in operating devices. Thereby, intermediate excited states involved in OLED operation can be investigated and the corresponding activation energy for both, intra‐ and intermolecular based TADF can be derived. Furthermore, a lower estimate is given for the extent of the triplet wavefunction to be ≥ 1.2 nm. Photoluminescence detected magnetic resonance (PLDMR) reveals the population of molecular triplets in optically excited thin films. Overall, the findings allow to draw a comprehensive picture of the spin‐dependent emission from intra‐ and intermolecular TADF OLEDs.

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“…The magnetic field effect (MFE) has been known as a fingerprint to directly identify the various spin-dependent processes of OLEDs (12)(13)(14)(15). MFE is defined as: MFE = [I(B) -I(0)]/I(0), where I(B) and I(0) are the measured intensities such as EL, current, voltage etc.…”

Section: Introductionmentioning

confidence: 99%

P‐126: Magnetic Field Effects on Electroplex‐Based Organic Light‐Emitting Diodes

Kim

Hong

Lee

et al. 2022

Symp Digest of Tech Papers

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An electroplex is an excited state charge transfer complex formed between a donor molecule and an acceptor molecule upon electrical excitation. Since the spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of electroplex is small likewise exciplex, the energy difference between the singlet and the triplet charge transfer (1CT and 3CT) states can be very small, which facilitate the conversion of triplet excitons into singlet excitons by the assistance of thermal energy and the emission as delayed fluorescence. However, in contrast to exciplex, the detailed analysis of the reverse intersystem crossing (RISC) from 3CT to 1CT and the exciton‐related annihilation processes in electroplex OLEDs have been rarely reported. In this talk, the magnetic field effects (MFEs) on the electroplex host using 2,2'‐di(9H‐carbazol‐9‐yl)‐1,1'‐biphenyl (oCBP) and 9‐(4,6‐bis(3‐(triphenylsilyl)phenyl)‐1,3,5‐triazin‐2‐yl)‐9H‐carbazole (DSiCzTrz) were investigated. Temperature‐dependent MFE measurements revealed that RISC channel co‐exists with the intersystem crossing (ISC) channel and triplet‐polaron quenching process prevails in the electroplex EML. It was also found that 3CT excitons behave as charge scattering sites.

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Direct Observation of Spin States Involved in Organic Electroluminescence Based on Thermally Activated Delayed Fluorescence

Cited by 11 publications

References 27 publications

Long-lived spin-polarized intermolecular exciplex states in thermally activated delayed fluorescence-based organic light-emitting diodes

Long-lived spin-polarized intermolecular exciplex states in thermally activated delayed fluorescence-based organic light-emitting diodes

Spin‐ and Voltage‐Dependent Emission from Intra‐ and Intermolecular TADF OLEDs

P‐126: Magnetic Field Effects on Electroplex‐Based Organic Light‐Emitting Diodes

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