Visualizing the radical-pair mechanism of molecular magnetic field effects by magnetic resonance induced electrofluorescence to electrophosphorescence interconversion

Kraus, Hermann; Bange, Sebastian; Frunder, Felix; Scherf, Ullrich; Boehme, Christoph; Lupton, John M.

doi:10.1103/physrevb.95.241201

Cited by 18 publications

(24 citation statements)

References 56 publications

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“…Embedding such emitters into host matrices of OLEDs potentially offers a window to spin statistics by discriminating between spinmixing mechanisms and other spin-dependent interactions which solely affect device resistance. Here, we demonstrate that a commercially available thiophene-free phenazine works equally well as a dual emitter, allowing us to visualize spin mixing in magnetic fields without having to resort to high-Z substituents [33].…”

Section: Introductionmentioning

confidence: 90%

“…Usually, the SOI is strongly enhanced by incorporating heavy atoms [30], an approach which is also known to perturb the molecule's immediate proximity and hence the actual molecular system of interest [31,32]. Incorporating trace amounts of covalently bound heavy atoms into polymeric materials offers one route to achieving sufficient spin-orbit coupling for the long-lived triplet state, but results in an inhomogeneous system that relies on triplet diffusion and cannot probe the pair process directly [33]. On the other hand, in organometallic emitters that directly incorporate the heavy atom, intersystem crossing is enhanced such that the singlet state is depleted and phosphorescence dominates the luminescence.…”

Section: Introductionmentioning

confidence: 99%

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Direct Detection of Singlet-Triplet Interconversion in OLED Magnetoelectroluminescence with a Metal-Free Fluorescence-Phosphorescence Dual Emitter

2018

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We demonstrate that a simple phenazine derivative can serve as a dual emitter for organic light-emitting diodes, showing simultaneous luminescence from the singlet and triplet excited states at room temperature without the need of heavy-atom substituents. Although devices made with this emitter achieve only low quantum efficiencies of < 0.2%, changes in fluorescence and phosphorescence intensity on the subpercent scale caused by an external magnetic field of up to 30 mT are clearly resolved with an ultra-low-noise optical imaging technique. The results demonstrate the concept of using simple reporter molecules, available commercially, to optically detect the spin of excited states formed in an organic light-emitting diode and thereby probe the underlying spin statistics of recombining electron-hole pairs. A clear anticorrelation of the magnetic-field dependence of singlet and triplet emission shows that it is the spin interconversion between singlet and triplet which dominates the magnetoluminescence response: the phosphorescence intensity decreases by the same amount as the fluorescence intensity increases. The concurrent detection of singlet and triplet emission as well as device resistance at cryogenic and room temperature constitute a useful tool to disentangle the effects of spin-dependent recombination from spindependent transport mechanisms.

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Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Direct Detection of Singlet-Triplet Interconversion in OLED Magnetoelectroluminescence with a Metal-Free Fluorescence-Phosphorescence Dual Emitter

2018

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“…Eqn (2), gives the product between the yield of triplet formation, F T , and the yield of singlet states formed by reverse intersystem crossing, F RISC defined in eqn (1). Simple examination of eqn (2) shows that triplet states are harvested with efficiency close to 100%, when the ratio between the delayed and prompt fluorescence components, F DF /F PF , is above three. Fig.…”

Section: Thermally Activated Delayed Fluorescencementioning

confidence: 99%

“…The localized nature of the excitons in organic materials gives rise to large exchange interactions, and leads to the formation of excited states with spin zero (singlet) and spin one (triplet). 1 In addition, a fraction of the singlet states (S 1 ) created upon charge recombination may also be converted into triplet states, due to intersystem crossing (ISC) caused by local hyperfine interactions, 2 or due to spin-orbit coupling. 3 Singlet and triplet states have significantly different photophysical characteristics.…”

Section: Introductionmentioning

confidence: 99%

The influence of molecular geometry on the efficiency of thermally activated delayed fluorescence

et al. 2019

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“…Details of the fabrication process are discussed in the Supporting Information. The OLEDs were placed on a stripline to generate the linearly polarized RF radiation of oscillating magnetic‐field amplitude B 1 , and positioned inside three pairs of Helmholtz coils to provide static magnetic fields B 0 of ≈50 nT precision and arbitrary orientation . Figure b shows a sketch of the arrangement.…”

Section: Figurementioning

confidence: 96%

Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

et al. 2020

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The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin‐1/2 Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π‐conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero‐field feature and local hyperfine fields. The zero‐field peak results from a quasistatic magnetic‐field effect of the RF radiation for periods comparable to the carrier‐pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero‐field peak, we suggest that this result may constitute a fundamental low‐field limit of magnetic resonance in carrier‐pair‐based systems. OLEDs offer an alternative solid‐state platform to investigate the radical‐pair mechanism of magnetic‐field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.

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Visualizing the radical-pair mechanism of molecular magnetic field effects by magnetic resonance induced electrofluorescence to electrophosphorescence interconversion

Cited by 18 publications

References 56 publications

Direct Detection of Singlet-Triplet Interconversion in OLED Magnetoelectroluminescence with a Metal-Free Fluorescence-Phosphorescence Dual Emitter

Direct Detection of Singlet-Triplet Interconversion in OLED Magnetoelectroluminescence with a Metal-Free Fluorescence-Phosphorescence Dual Emitter

The influence of molecular geometry on the efficiency of thermally activated delayed fluorescence

Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

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