Synthesis and Exciton Dynamics of Donor-Orthogonal Acceptor Conjugated Polymers: Reducing the Singlet–Triplet Energy Gap

Freeman, David M.E.; Musser, Andrew J.; Frost, Jarvist M.; Stern, Hannah L.; Forster, Alexander K.; Fallon, Kealan J.; Rapidis, Alexandros G.; Cacialli, Franco; McCulloch, Iain; Clarke, Tracey M.; Friend, Richard H.; Bronstein, Hugo

doi:10.1021/jacs.7b03327

Cited by 98 publications

(85 citation statements)

References 37 publications

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“…This is a critical distinction from inorganic excitonpolaritons that has not yet been addressed in the literature. The existence of this state mixing is a critical driver in photophysical processes such as ultrafast intersystem crossing 45 , thermally activated delayed fluorescence 46 , singlet exciton fission 42,44 and its reverse, triplet-triplet annihilation. For example, in singlet fission the nominal S1 state contains both CT and TT character, in some cases such as pentacene films to a surprisingly high degree (circa 50% CT) 47 .…”

Section: Discussionmentioning

confidence: 99%

Manipulating molecules with strong coupling: harvesting triplet excitons in organic exciton microcavities

et al. 2020

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Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of materials. Organic semiconductors are of current interest for their room-temperature polariton formation. However, within organic optoelectronic devices, it is often the 'dark' spin-1 triplet excitons that dominate operation. These triplets have been largely ignored in treatments of polariton physics. Here we demonstrate polariton population from the triplet manifold via triplettriplet annihilation, leading to polariton emission that is longer-lived (>μs) even than exciton emission in bare films. This enhancement arises from spin-2 triplet-pair states, formed by singlet fission or triplet-triplet annihilation, feeding the polariton. This is possible due to state mixing, which -in the strong coupling regime-leads to sharing of photonic character with states that are formally non-emissive. Such 'photonic sharing' offers the enticing possibility of harvesting or manipulating even states that are formally dark.

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Section: Discussionmentioning

confidence: 99%

Manipulating molecules with strong coupling: harvesting triplet excitons in organic exciton microcavities

et al. 2020

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“…proposed a strategy to induce TADF property in bridged aromatic moieties named as “ D‐oA ” which means introducing orthogonal acceptor groups at the bridgehead position of alternating fluorene repeat units. They carefully analyzed the contribution of CN group in inducing TADF properties in ASFCN compared with non‐TADF polymer ASFH ( Figure ) and concluded that CN group can effectively reduce CT stated below 3 (π−π*) and unlock TADF properties …”

Section: Tadf Polymersmentioning

confidence: 99%

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

Wei

Voit

2018

Macromol. Rapid Commun.

117

100

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several organic layers like hole injection layer, hole-and electron transport layer, and most importantly, the emissive layers (EML), inserted between the electrodes (Figure 1). Under external voltage, opposite charge carriers of holes and electrons are injected from anode and cathode and finally recombined to produce photons within the EML. [10][11][12] Emitters can largely determine not only the performance but also the processing methods of devices, and therefore they are the key material among all the components of the OLEDs. During the past three decades, the emitter materials have seen a rapid progress, from traditional fluorescent, phosphorescent, and triplet-triplet annihilation (TTA) materials into the era of thermally activated delayed fluorescent (TADF) materials, and from small molecules to polymers. [13] According to spin statistics, singlet and triplet excitons are formed within the EML at the ratio of 1:3, when OLED devices are working under electrical excitation; however, the organic emitters have different capabilities to utilize the exciton to induce photons which results in different efficiencies of OLED devices. The electricity-photon conversion efficiency of OLED can be evaluated by the quantum efficiency (QE), referring to the numeral ratio of photons to the injected electronhole pairs. [14,15] QE can be further subdivided into internal quantum efficiency (IQE) and external quantum efficiency (EQE). The IQE, defined as photon generation within the EML, is directly determined by the emitters, [16] while EQE refers to the numerical ratio of total photons emitting out of the device to the charge pairs injected. Since the photons are generated within and emitted out from the EML, the chemical structure of the emitter and the resulting properties can deeply influence the device efficiency. The traditional fluorescent emitters can only take advantages of singlet excitons for luminescence, with maximal IQE of roughly 25%. Given that out-coupling efficiency is normally 20%, the maximal EQE is only 5%, far below expectation. Phosphorescent OLEDs have the capability to reach 100% IQE, because phosphorescent emitters usually contain heavy atoms like iridium or platinum to harvest both, singlet and triplet excitons for phosphorescence through significant spin-orbit coupling, but the heavy metals usually bring about serious issues of comparable high costs and low long-term stability in OLEDs. [17] TTA fluorescent emitters can only reach a maximum IQE of 62.5% through conversion of two triplet excitons into one singlet exciton, and show mainly blue emission. [18] TADF materials, however, can harvest triplet Organic Light-Emitting Diodes Thermally activated delayed fluorescent (TADF) polymers are promising emitting materials to realize highly efficient, large-scale, and low-cost organic light-emitting diodes (OLEDs) since they exhibit various advantages such as heavy-metal-free structures, 100% theoretical internal quantum efficiency, and ease of large-area fabrication through solution process. At present,...

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“…16 Finally, the fact that in BPyrD5 triplet state formation was not observed may be associated with the molecular geometry in this dyad. It has been noted in previous works that an orthogonal arrangement of the subunits in multichromophoric systems provides efficient ISC, e.g., in donor-orthogonal-acceptor conjugated polymers [36] and OLED emitters exhibiting thermallyactivated delayed fluorescence. [37] Our recent study showed that the orthogonal geometry in BADs is responsible for reducing the S-T energy gap in the CT state.…”

Section: Articlementioning

confidence: 99%

BODIPY‐Pyrene and Perylene Dyads as Heavy‐Atom‐Free Singlet Oxygen Sensitizers

et al. 2018

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Synthesis and Exciton Dynamics of Donor-Orthogonal Acceptor Conjugated Polymers: Reducing the Singlet–Triplet Energy Gap

Cited by 98 publications

References 37 publications

Manipulating molecules with strong coupling: harvesting triplet excitons in organic exciton microcavities

Manipulating molecules with strong coupling: harvesting triplet excitons in organic exciton microcavities

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

BODIPY‐Pyrene and Perylene Dyads as Heavy‐Atom‐Free Singlet Oxygen Sensitizers

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