Tuning the Singlet–Triplet Gap in Metal‐Free Phosphorescent π‐Conjugated Polymers

Chaudhuri, Debangshu; Wettach, Henning; Schooten, Kipp J. van; Liu, Su; Sigmund, Eva; Höger, Sigurd; Lupton, John M.

doi:10.1002/anie.201003291

Cited by 45 publications

(41 citation statements)

References 61 publications

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“…The diamond core complex reported by Deaton yields green devices with external quantum efficiency of 16.1%, close to that obtainable with Ir-based phosphors [128]. Further, there are also reports of all organic emitters which have low Δ ST and appreciable E-type contribution [132]. Endo et al have reported devices based on this mechanisms giving 5.3% EQE in the blue/green [133,134].…”

Section: Alternative Ways To Produce Singlet Excitons From Triplet Stmentioning

confidence: 52%

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: Alternative Ways To Produce Singlet Excitons From Triplet Stmentioning

confidence: 52%

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

Monkman

2013

ISRN Materials Science

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“…We recently reported a series of triphenylene copolymers with tuneable singlet-triplet energy difference DE ST . 6 To investigate whether plasmonic field-mediated singlet-triplet crossover is sensitive to DE ST , we extended our study to compounds 3 …”

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confidence: 99%

Plasmonic surface enhancement of dual fluorescence and phosphorescence emission from organic semiconductors: effect of exchange gap and spin–orbit coupling

Chaudhuri

Sigmund

et al. 2012

Chem. Commun.

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Dual singlet-triplet fluorescence-phosphorescence emitting compounds demonstrate that plasmonic surface enhancement is controlled solely by the underlying oscillator strength of a transition: metal-free compounds with weak spin-orbit coupling show no enhancement in phosphorescence efficiency even though fluorescence is amplified.Excitement in the area of plasmonics stems from the ability to detect processes that are otherwise undetectable. Collective electron oscillations at metal surfaces experience strong spatial localization, which results in extremely intense and localized electromagnetic fields. This phenomenon is at the heart of all surface-enhanced spectroscopic processes. 1 The intense local field can relax several selection rules, thereby allowing transitions that are otherwise forbidden, and are therefore inaccessible to regular spectroscopy. While observation of forbidden Raman modes in surface-enhanced Raman scattering (SERS) is well documented, 2 the same is not as common for electronic transitions. Particularly noteworthy is a report on the observation of dipole-forbidden, but quadrupole-allowed transitions in conjugated oligoenes near silver films. 3 A crucial question to explore is hence whether metal nanostructures can also enhance dipole-forbidden radiative recombination from triplet excited states, phosphorescence. The necessity arises because 75% of radical-pair recombination events in an organic light-emitting diode (OLED) lead to triplet excited states that generally have poor radiative recombination efficiency in the absence of heavy-metal atoms. There have been a few reports on plasmon-enhanced phosphorescence. 4 One aspect common to these studies is that the effect was investigated in materials that are strongly spin-orbit (SO) coupled and thus highly phosphorescent to begin with. Most hydrocarbon organic semiconductors are weakly phosphorescent. OLED electrodes provide a natural environment for surface enhancement. If surface enhancement were to apply to transitions involving pure triplet and singlet states, in the absence of SO-induced spin mixing, the mechanism could open a new intrinsic radiative channel in an OLED, changing the way triplet harvesting is achieved and removing present limitations on triplet emitters posed by organometallic chemistry.Unfortunately, as we demonstrate here, this approach will not succeed. Phosphorescence can only be enhanced by plasmonics when intersystem crossing (ISC) is already strong. Surprisingly, phosphorescence due to transitions between pure triplet and singlet states is not enhanced to any measurable extent by plasmonic effects, even though a strong increase in fluorescence is observed in dual singlet-triplet-emitting compounds.To assess the possibility of surface enhancement of phosphorescence, we need an independent observable to confirm the presence of an enhancement effect. This observable is given by the dipole-allowed singlet transition in the dual-emitting compounds shown in Fig. 1a. We chose four materials with variable triplet yield (...

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“…Some of the most relevant problems in the field of condensed matter, nanoscience, and renewable energy applications are related to the discovery and understanding of complex materials engineered to meet a specific functionality . Renewed interest in the use of conjugated molecules with delocalized π electrons as key components in nanoscale electronics and optoelectronic devices has motivated recent abilities to construct single‐molecule junctions and measure their transport properties .…”

Section: Introductionmentioning

confidence: 99%

From charge‐transfer excitations to charge‐transport phenomena in organic molecular crystals

Zoppi

Baldridge

2017

Int J of Quantum Chemistry

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Functional devices based on properties inherent in single organic molecules offer promise for use in technological applications, particularly building blocks that can take on diverse electronic functions with tuning through chemical design and synthesis. Morphological features of curved aromatic structures offer exploration into a wealth of phenomenology as a function of environment, such as exemplified for super atomic molecular orbitals. This review discusses current stateof-the-art electronic structure approaches for prediction of structural, electronic, optical, and transport properties of planar and curved designed components. Important principle for design lies in understanding and control of the solid-state packing and intermolecular interactions of individual building block units, for which many body perturbation techniques are essential. Molecular and solid state engineering is shown to be effective toward tailoring new materials with optimal transport properties, with valuable insight provided by high level computational prediction.charge transfer, charge transport, curved aromatics, GW-BSE theory, SAMO | I N TR ODU C TI ONSome of the most relevant problems in the field of condensed matter, nanoscience, and renewable energy applications are related to the discovery and understanding of complex materials engineered to meet a specific functionality. [1][2][3] Renewed interest in the use of conjugated molecules with delocalized p electrons as key components in nanoscale electronics and optoelectronic devices has motivated recent abilities to construct singlemolecule junctions and measure their transport properties. [4][5][6] As conductor dimensions approach the nanoscale, design principles turn toward creation of molecules with tunable functionality to enable control of charge transport on the molecular scale. [5,7] Organic-organic (hybrid) interfaces are primary components in emerging technologies, such as organic and molecular electronics [8] and photovoltaic cells.[9] These complex systems can often strongly influence the electrical and optical characteristics of a specific structure or device.[10] Key material properties, such as the level alignment at functional interfaces, [11,12] the ability of charge carriers to be injected into a conductive substrate, the efficiency of optical excitations to split into free carriers, [13] and so on, poorly described within standard density functional theory (DFT) methodologies, [14] are ultimately factors in determining unique electronic properties of a given complex. As such, pressing needs have emerged for improved understanding of the details involved in optimization and control of electronic transport phenomena in aromatic systems, two key representative components of which constitutes the focus of the present work.I. The conventional mechanism for charge transport in conjugated materials involves the overlap of delocalized p molecular orbitals, which extend through a plane and can facilitate transport. Directed confinement of electronic states in one...

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Tuning the Singlet–Triplet Gap in Metal‐Free Phosphorescent π‐Conjugated Polymers

Cited by 45 publications

References 61 publications

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

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

Plasmonic surface enhancement of dual fluorescence and phosphorescence emission from organic semiconductors: effect of exchange gap and spin–orbit coupling

From charge‐transfer excitations to charge‐transport phenomena in organic molecular crystals

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