Photon upconversion based on sensitized triplet–triplet annihilation

Singh-Rachford, Tanya N.; Castellano, Felix N.

doi:10.1016/j.ccr.2010.01.003

Cited by 1,310 publications

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“…This reaction obeys spin conservation and is referred to as triplet fusion or TTA-UC in the upconversion literature. [9][10][11][12][13][14] In Stage III, the triplet-fusion-generated singlet recombines and produces delayed emission.…”

Section: Doi: 101002/adma201605987mentioning

confidence: 99%

“…[6][7][8] At the same time, photon upconversion through TTA has been widely considered for next-generation photovoltaic applications. [9][10][11][12][13][14] Effective upconverters have been demonstrated using combinations of a triplet sensitizer such as platinum octaethylporphyrin (PtOEP) [3] and a triplet acceptor/annihilator such as 9,10-diphenylanthracene (DPA), [15] perylene, [16] or rubrene.[17] TTA-upconversion (TTA-UC) quantum yield (ratio of upconverted photons to absorbed photons) of 30% was observed in solution phase. [18] This suggests that the intrinsic efficiency of the TTA-UC reaction (i.e., the This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.…”

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Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

et al. 2017

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probability of a triplet pair forming a singlet) in solution is >60%, much higher than the spin-statistical prediction of 25% (one pair of triplets collides to form one of the four states: one singlet S 1 and three triplets T 1 , assuming higher triplet and quintet states are inaccessible). Practical application of solar energy conversion requires the TTA-UC material to be in solid state rather than in solution phase. However, the TTA-UC quantum yield of solidstate systems remains low, typically below 5%, [10] and is moderately high (about 10%) in only one example. [19] To achieve high efficiencies, high excitation intensities (200 mW cm −2 or above) are commonly required. These imply that in solid state, the experimentally observed reaction efficiency of TTA-UC was up to about 20%, below the 25% spin-statistical limit.To achieve highly efficient triplet fusion (TTA-UC) in OLEDs and other TTA upconverters, we consider four criteria for the selection of emitters: (1) high fluorescence quantum yield, (2) short singlet lifetime, (3) long triplet lifetime, and (4) the energy of two triplet excitons, 2E(T 1 ) lies slightly above that of the singlet exciton, E(S 1 ), but below the second triplet state, E(T 2 ) (and also the energies of any spin-quintet states) (E(S 1 ) ≲ 2E(T 1 ) < E(T 2 )). The first and second criteria are prerequisites for efficient fluorescence. The third criterion is essential for the accumulation of a sufficiently high triplet population density required for rapid triplet-triplet collision processes. The fourth criterion ensures that higher-lying triplet or quintet states do not provide loss channels. The spin states of the triplet excitons give in principle nine spin configurations for the interacting triplet exciton pair, five associated with a quintet, three with a triplet, and one with the singlet state. It is generally considered that the quintet is always higher in energy than the initial triplet pair, so is neglected. If there are no energetically accessible higher-lying triplet states at E(T 2 ), we expect only the S 1 and T 1 excitons to form. Triplets produced from this reaction can be recycled and participate in a further fusion reaction. [7] The basic working principle of a triplet fusion LED (FuLED) is illustrated in Figure 1a. The initial stage (Stage I) of the device operation includes charge injection and exciton formation. Exciton formation on the emissive molecules may occur directly or indirectly through an additional exciton transfer step from a host material. If a host material is present, the S 1 and T 1 of the host are required to be higher than that of the emitter to allow efficient host-emitter energy transfer and to ensure long triplet lifetime of the emitter (Criterion 3 discussed above). The 25% singlet population can be converted to light emission (and nonradiative losses) from the singlet channel immediately, resulting in prompt electroluminescence (EL). The 75% triplet excitons remain nonemissive, but the population of triplets is When an organic light-emitting dio...

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Section: Doi: 101002/adma201605987mentioning

confidence: 99%

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confidence: 99%

Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

et al. 2017

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“…For this upconversion mechanism, the sensitizer and emitter are both organic molecules, and the triplet state of these organic molecules is used as the intermediate state in the upconversion process. 51 TTA-based UCL processes benefit from the high absorption cross-section of organic dyes and the highly efficient TTA process between emitter molecules that usually have much stronger absorption and higher UCL efficiencies than lanthanide-based UCL processes. To date, the highest quantum efficiency reported for TTA-based UCL processes exceeds 40%, 52 and some systems have proven to be functional under excitation from only sunlight.…”

Section: Ucnps For In Vivo Applications W Feng Et Almentioning

confidence: 99%

“…To date, the highest quantum efficiency reported for TTA-based UCL processes exceeds 40%, 52 and some systems have proven to be functional under excitation from only sunlight. 51 The problem limiting bioapplications of TTA-based upconversion materials is that the TTA process needs to occur in a medium with proper liquidity to ensure opportunities for collisions between the emitters and sensitizers so that energy transfer takes place. Therefore, TTA-based materials cannot be used for in vivo bioapplications until a suitable assembly method is developed to obtain upconversion nanoparticles with fluxible, or at least flexible, media inside.…”

Section: Ucnps For In Vivo Applications W Feng Et Almentioning

confidence: 99%

Recent advances in the optimization and functionalization of upconversion nanomaterials for in vivo bioapplications

Feng

Zhu

2013

NPG Asia Mater

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Upconversion nanophosphors are considered to be important components in advanced materials designed for in vivo bioapplications and benefit from their unique anti-Stokes upconversion luminescence properties. The near-infrared light excitation allows for a large penetration depth in biotissues during in vivo applications. This review presents recent advances in the optimization and functionalization of upconversion nanomaterials for bioimaging and in vivo therapy. The most effective protocols are introduced in detail. Current limitations and future prospects are also included to provide a general summary and suggest future research directions.

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“…Namely, in most cases the triplet state of the acceptor must be lower in energy than the triplet state of the sensitizer and both triplet states must be long lived (e.g. microseconds) as the TTA process is bimolecular and relies on diffusional interactions; furthermore, the singlet state of the acceptor must be higher energy than the singlet state of the sensitizer, yet less than or equal to twice the energy of the triplet state of the acceptor (Scheme 1) [25,26]. Thus, metalcontaining chromophores with long-lived triplet states make desirable triplet sensitizers because the energy and excited state lifetimes of the singlet and triplet states can be rationally tuned by ligand modification [27,28].…”

Section: Introductionmentioning

confidence: 99%

Photon upconversion sensitized by a Ru(II)-pyrenyl chromophore

Deng

Lazorski

Castellano

2015

Phil. Trans. R. Soc. A.

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One contribution of 11 to a discussion meeting issue 'Organic semiconductor spintronics: utilizing triplet excitons in organic electronics' . The near-visible-to-blue singlet fluorescence of anthracene sensitized by a ruthenium chromophore with a long-lived triplet-excited state, [Ru(5-pyrenyl-1,10-phenanthroline) 3 ](PF 6 ) 2 , in acetonitrile was investigated. Low intensity non-coherent green light was used to selectively excite the sensitizer in the presence of micromolar concentrations of anthracene generating anti-Stokes, singlet fluorescence in the latter, even with incident power densities below 500 µW cm −2 . The resultant data are consistent with photon upconversion proceeding from sensitized triplet-triplet annihilation (TTA) of the anthracene acceptor molecules, confirmed through transient absorption spectroscopy as well as static and dynamic photoluminescence experiments. Additionally, quadratic-to-linear incident power regimes for the upconversion process were identified for this composition under monochromatic 488 nm excitation, consistent with a sensitized TTA mechanism ultimately producing the anti-Stokes emission characteristic of anthracene singlet fluorescence.

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Photon upconversion based on sensitized triplet–triplet annihilation

Cited by 1,310 publications

References 88 publications

Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

Recent advances in the optimization and functionalization of upconversion nanomaterials for in vivo bioapplications

Photon upconversion sensitized by a Ru(II)-pyrenyl chromophore

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