Effects of triplet exciton confinement induced by reduced conjugation length in polyspirobifluorene copolymers

Rothe, Carsten; Brunner, K.; Bach, Ingrid; Heun, Susanne; Monkman, Andrew P.

doi:10.1063/1.1851505

Cited by 16 publications

(14 citation statements)

References 26 publications

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“…From magnetic field dependencies of the TTA process, they conclude that in fact TTA contributes substantially to the final singlet yield. We have also shown that at room temperature, the typical triplet exciton lifetime reduces to below 250 ns compared to >1 s at 10 K [125]; this in part is due to TTA but also other nonradiative pathways may become more efficient, this gives rise to the substantial temperature dependence of the ELQY we find in fluorescence devices as discussed above.…”

Section: Historical Perspective On Ttamentioning

confidence: 75%

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

Monkman

2013

ISRN Materials Science

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A potential major drawback with organic light-emitting devices, (OLEDs) is the limit of 25% singlet exciton production through spin-dependent charge recombination. Recent device results, however, show that this limit does not hold and far higher efficiencies can be achieved in purely fluorescent-based systems (Wohlgenannt et al. (2012)). Here, the various routes by which triplet excitons can generate singlet states are discussed and their relative contributions to the overall electroluminescence yield are given. The materials requirements to obtain maximum singlet production from triplet states are discussed. These triplet contributions can give very high device yields for fluorescent emitters, which in the case of blue devices can be highly advantageous. Further, new devices architectures open up which are simple and have intrinsically low turn on voltages, ideal for large-area OLED lighting applications.

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Section: Historical Perspective On Ttamentioning

confidence: 75%

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

Monkman

2013

ISRN Materials Science

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“…An important feature of many conducting polymers is that the triplet state seems to be highly localised on a small number of repeat units whereas the corresponding singlet excited state is more extensively delocalised. [29] This behaviour is evident from the disparate delocalisation lengths extracted from spectral curve fitting routines. In turn, this realisation raises concerns about the exact nature of the intersystem-crossing process and also about the delocalisation length of higher-lying triplet states.…”

Section: Introductionmentioning

confidence: 95%

On the Conjugation Length for Oligo(ethynylnaphthalene)‐Based Molecular Rods

Benniston

Harriman

Rewinska

et al. 2007

Chemistry A European J

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The synthesis is described for a small series of oligomers built from (2, 3, 4 or 6) ethynyl-naphthalene repeat units and end-capped with solubilising 1,2,3-tris-dodecyloxy-benzene groups. These compounds absorb in the near-UV region and exhibit strong fluorescence in both fluid solution and a glassy matrix at 77 K. The spectral profiles are fully consistent with a structurally heterogeneous ground state becoming more planar upon excitation and with the low-temperature glass further stabilising the co-planar orientation. The absorption and fluorescence maxima move towards lower energy with increasing number of repeat units and there is a corresponding increase in the Huang-Rhys factor for the radiative process. The non-radiative rate constants also depend on molecular length and are well explained in terms of the energy-gap law. In contrast, very weak phosphorescence is observed at 77 K for which the peak maximum and lifetime remain insensitive to the number of naphthalene units. The triplet lifetimes recorded at ambient temperature are also independent of the molecular length but the triplet-triplet absorption spectra change throughout the series. These results are discussed in terms of the degree of electronic coupling between adjacent repeat units for each of the relevant excited states. During these studies it was noted that the rate of intersystem crossing to the triplet manifold is but weakly affected by heavy-atom perturbers. A non-fluorescent complex is formed between iodoethane and the molecular rod but the corresponding bimolecular process occurs at well below the diffusion-controlled limit. This behaviour is considered in terms of spin-orbit coupling between the excited states and takes account of the differing conjugation lengths.

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“…All data are consistent in spectral shape and energetic position with other polyfluorene derivatives and earlier investigations on polyspirobifluorene, respectively. 7,15,16,[19][20][21] First the influence of an applied electric field on the triplet exciton was investigated. After optical excitation, triplets in conjugated polymers are formed due to inter-system-crossing ͑ISC͒ in a sequential process from the initially excited singlet excitons; with an efficiency for PSF of 6.0%.…”

Section: Introductionmentioning

confidence: 99%

“…Under such conditions the triplet lifetimes of conjugated polymers are typically of the order of one second. 16,19,21 Then, both the triplet emission and the transient absorption are available as tools to probe the triplet exciton. However, since the time resolution of the phosphorescence detection is only about 10 ms, and these measurements are made pointwise, i.e., they are time consuming, 19 for the present purpose probing the transient triplet absorption is deemed the superior method.…”

Section: Introductionmentioning

confidence: 99%

Electric-field-induced singlet and triplet exciton quenching in films of the conjugated polymer polyspirobifluorene

2005

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An experimental investigation into the low-temperature electric-field-induced quenching of the transient triplet absorption and the prompt and delayed fluorescence of the conjugated polymer polyspirobifluorene is presented. A maximal instantaneous triplet exciton quenching of about 25% is observed for an electric field of 2.5ϫ 10 6 V / cm. The fluorescence intensity under such conditions is quenched by 97%, which, to our knowledge, is the highest value ever reported for a conjugated polymer. A comparison of the absolute singlet and triplet exciton quenching yields a singlet exciton binding energy of approximately 0.38 eV. The delayed fluorescence in the above polymer is known to be caused by bimolecular triplet annihilation, which has been further substantiated using electric-field quenching experiments. Further, earlier experiments, which seem to verify the geminate pair origin for the delayed fluorescence of the laddertype polymer poly͑para-phenylene͒ ͑MeLPPP͒, are discussed and re-evaluated using the above polyfluorene derivative.

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Effects of triplet exciton confinement induced by reduced conjugation length in polyspirobifluorene copolymers

Cited by 16 publications

References 26 publications

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

On the Conjugation Length for Oligo(ethynylnaphthalene)‐Based Molecular Rods

Electric-field-induced singlet and triplet exciton quenching in films of the conjugated polymer polyspirobifluorene

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