Interplanar interactions in the excited triplet states of carbazole dimers by means of time-resolved EPR spectroscopy

Saiful, Islam S. M.; Heinze, P.; Ohba, Yasunori; Yamauchi, Seigo; Yamamoto, Masahide; Tohda, Yasuo; Tani, Keita

doi:10.1080/00268970600638606

Cited by 11 publications

(18 citation statements)

References 23 publications

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“…4 ), and EEEAAA polarisation pattern of DTCz-DPS-1 are all typical of triplet states in organic chromophores 51 . These parameters are consistent with the 3 LE associated with the carbazole monomer 53 , leading us to attribute the trESR signal to a triplet exciton localised on the carbazole donor. The trESR signals of DTCz-DPS-2 and -3 (Fig.…”

Section: Resultssupporting

confidence: 82%

“…Use of a Stanford Research SR560 low-noise preamplifier of the Schottky diode-detected CW Mode signal at 3–300 kHz was in substitute of the video amplifier, following verification against the quadrature mix-down DC-AFC Transient Mode signal of 20 MHz bandwidth setting. Spectra were recorded for between 4 and 12 h. Data was processed with MatLab (The Mathworks, Natick, N.J.) and ESR simulations made use of the EasySpin routines 53 .…”

Section: Methodsmentioning

confidence: 99%

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Electron spin resonance resolves intermediate triplet states in delayed fluorescence

et al. 2021

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Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.

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Section: Resultssupporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

et al. 2021

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“…Thus this state can be assigned to a 3 LE state confined on the carbazole moiety; this is supported by the ZFS D of the triplet state of native carbazole 107 mT. 78 For DTCz-DPS-2 and DTCz-DPS-3 , however, two triplet states are required for satisfactory simulation of the experimental TREPR spectra. For DTCz-DPS-2 , one triplet is with ZFS D and E parameters of −108 mT and −9 mT, respectively (Table 3).…”

Section: Trepr Spectroscopy: Detection Of the Transient Paramagnetic ...mentioning

confidence: 77%

Application of time-resolved electron paramagnetic resonance spectroscopy in the mechanistic study of thermally activated delayed fluorescence (TADF) materials

2022

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“…The ZFS parameters (|D|, |E| = 108, 9 mT), position of the half-field transition (161 mT, Supplementary Fig. 4), and EEEAAA polarisation pattern of DTCz-DPS-1 are typical of triplet states in organic chromophores 51 and, in particular, are consistent with the 3 LE associated with the carbazole monomer 53 , leading us to attribute the trESR signal to a triplet exciton localised on the carbazole donor.…”

Section: Design and Detection Of Multiple Triplet Excitonic Statesmentioning

confidence: 64%

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Drummond

Aizawa

Zhang

et al. 2021

Preprint

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Molecular organic fluorophores are currently used in organic light-emitting diodes, though nonemissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.

show abstract

Interplanar interactions in the excited triplet states of carbazole dimers by means of time-resolved EPR spectroscopy

Cited by 11 publications

References 23 publications

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Application of time-resolved electron paramagnetic resonance spectroscopy in the mechanistic study of thermally activated delayed fluorescence (TADF) materials

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

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