Ultra-small PbS nanocrystals as sensitizers for red-to-blue triplet-fusion upconversion

Imperiale, Christian J.; Green, Philippe B.; Hasham, Minhal; Wilson, Mark W.

doi:10.1039/d1sc04330g

Cited by 25 publications

(60 citation statements)

References 100 publications

(227 reference statements)

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“…With their photoactive 3 ILCT excited states, both [Zn( m -L) 2 ] and [Zn( p -L) 2 ] should in principle be able to sensitize triplet–triplet annihilation upconversion, which is an attractive process for the conversion of low-energy input light into higher energy output radiation. ,− In particular, upconversion from the visible to the ultraviolet spectral region has received increasing interest lately, − and our Zn II complexes with their relatively high 3 ILCT energies seemed promising for this purpose. Previous upconversion studies with Zn II sensitizers focused on red-to-blue upconversion and on near-infrared sensitization of photochemical reactions. − We identified the combination of [Zn( m -L) 2 ] and (TMS) 2 napht (Figure e) as particularly promising for blue to UV upconversion.…”

Section: Results and Discussionmentioning

confidence: 99%

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Kübler

Pfund

Wenger

2022

JACS Au

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Many CuI complexes have luminescent triplet charge-transfer excited states with diverse applications in photophysics and photochemistry, but for isoelectronic ZnII compounds, this behavior is much less common, and they typically only show ligand-based fluorescence from singlet π–π* states. We report two closely related tetrahedral ZnII compounds, in which intersystem crossing occurs with appreciable quantum yields and leads to the population of triplet excited states with intraligand charge-transfer (ILCT) character. In addition to showing fluorescence from their initially excited 1ILCT states, these new compounds therefore undergo triplet–triplet energy transfer (TTET) from their 3ILCT states and consequently can act as sensitizers for photo-isomerization reactions and triplet–triplet annihilation upconversion from the blue to the ultraviolet spectral range. The photoactive 3ILCT state furthermore facilitates photoinduced electron transfer. Collectively, our findings demonstrate that mononuclear ZnII compounds with photophysical and photochemical properties reminiscent of well-known CuI complexes are accessible with suitable ligands and that they are potentially amenable to many different applications. Our insights seem relevant in the greater context of obtaining photoactive compounds based on abundant transition metals, complementing well-known precious-metal-based luminophores and photosensitizers.

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Section: Results and Discussionmentioning

confidence: 99%

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Kübler

Pfund

Wenger

2022

JACS Au

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“…The long-lived delayed PL kinetics in NC473-PTA (Figure d, red line) further evidence thermally activated rTET from sensitized PTA triplets back to NC473, indicating that the acceptor states are indeed lower than the donor states in terms of their Gibbs free energy. In contrast, if TET-1 is assumed to proceed via thermal activation, as has been observed in recent Silicon and PbS NC-based systems, , we should expect the reverse process of TET-1 (r-TET-1 from PTA triplets to NCs) to be even faster than TET-1 , the rates of these two being related through a Boltzmann factor. In this case, we would not observe the long-lived delayed PL from NC473-PTA .…”

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confidence: 92%

Entropy-Powered Endothermic Energy Transfer from CsPbBr₃ Nanocrystals for Photon Upconversion

Han

Guo

et al. 2022

J. Phys. Chem. Lett.

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Colloidal semiconductor nanocrystals as triplet photosensitizers are characterized by a negligible intersystem crossing energy loss as compared to that of traditional molecular sensitizers. This property in principle allows for a large apparent anti-Stokes shift in sensitized triplet–triplet annihilation photon upconversion (TTA-UC) for a variety of applications. In previous systems, however, this advantage is largely erased by the energy loss associated with energy transfer from nanocrystals to surface-anchored triplet transmitter molecules. Here we report visible-to-ultraviolet TTA-UC from 473 to 355 nm, corresponding to an apparent anti-Stokes shift of 0.87 eV, with a quantum efficiency that reaches 4.5% (normalized at 100%). The system consists of CsPbBr3 nanocrystal sensitizers, phenanthrene transmitters, and diphenyloxazole annihilators. Time-resolved spectroscopy reveals that triplet energy transfer from CsPbBr3 nanocrystals to phenanthrene can be endothermic yet efficient thanks to a sizable entropic gain. This study exemplifies how entropic effects can be harnessed to enhance or control a plethora of applications with nanocrystals as photosensitizers.

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“…For solar applications, the mechanism called triplet–triplet annihilation photon UC (TTA-UC) is of specific interest as this process functions under low-intensity, noncoherent light. , By using a donor, or sensitizer, species in conjunction with a fluorescent annihilator, triplets generated by the sensitizer from incident long-wavelength light may be converted into a highly energetic singlet state within the annihilator species in a spin-allowed TTA process. This scheme has been demonstrated for many different spectral ranges and with a variety of compounds, spanning purely organic systems, , nanocrystals, − metallic complexes, − and metal–organic frameworks, to name a few.…”

Section: Introductionmentioning

confidence: 99%

Approaching the Spin-Statistical Limit in Visible-to-Ultraviolet Photon Upconversion

et al. 2022

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Triplet–triplet annihilation photon upconversion (TTA-UC) is a process in which triplet excitons combine to form emissive singlets and holds great promise in biological applications and for improving the spectral match in solar energy conversion. While high TTA-UC quantum yields have been reported for, for example, red-to-green TTA-UC systems, there are only a few examples of visible-to-ultraviolet (UV) transformations in which the quantum yield reaches 10%. In this study, we investigate the performance of six annihilators when paired with the sensitizer 2,3,5,6-tetra(9 H -carbazol-9-yl)benzonitrile (4CzBN), a purely organic compound that exhibits thermally activated delayed fluorescence. We report a record-setting internal TTA-UC quantum yield (Φ UC,g ) of 16.8% (out of a 50% maximum) for 1,4-bis((triisopropylsilyl)ethynyl)naphthalene, demonstrating the first example of a visible-to-UV TTA-UC system approaching the classical spin-statistical limit of 20%. Three other annihilators, of which 2,5-diphenylfuran has never been used for TTA-UC previously, also showed impressive performances with Φ UC,g above 12%. In addition, a new method to determine the rate constant of TTA is proposed, in which only time-resolved emission measurements are needed, circumventing the need for more challenging transient absorption measurements. The results reported herein represent an important step toward highly efficient visible-to-UV TTA-UC systems that hold great potential for driving high-energy photochemical reactions.

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Ultra-small PbS nanocrystals as sensitizers for red-to-blue triplet-fusion upconversion

Abstract: We demonstrate the use of ultra-small PbS quantum dots as endothermic sensitizers for red-to-blue triplet-fusion upconversion, achieving nanocrystal-sensitized upconversion photochemistry.

Cited by 25 publications

References 100 publications

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Entropy-Powered Endothermic Energy Transfer from CsPbBr₃ Nanocrystals for Photon Upconversion

Approaching the Spin-Statistical Limit in Visible-to-Ultraviolet Photon Upconversion

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Ultra-small PbS nanocrystals as sensitizers for red-to-blue triplet-fusion upconversion

Abstract: We demonstrate the use of ultra-small PbS quantum dots as endothermic sensitizers for red-to-blue triplet-fusion upconversion, achieving nanocrystal-sensitized upconversion photochemistry.

Cited by 25 publications

References 100 publications

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Entropy-Powered Endothermic Energy Transfer from CsPbBr3 Nanocrystals for Photon Upconversion

Approaching the Spin-Statistical Limit in Visible-to-Ultraviolet Photon Upconversion

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Entropy-Powered Endothermic Energy Transfer from CsPbBr₃ Nanocrystals for Photon Upconversion