Optically active materials able to up‐convert the frequency of the incident radiation can be used to enhance the performance of photovoltaic and photocatalityc cells, recovering sub‐bandgap photons not directly absorbed by the devices. Actually, sensitized up‐conversion (SUC) based on multi‐component organic systems is the most promising approach for these photon energy managing processes, being efficient also at the solar irradiance. However, applications of SUC on real devices have not been yet accomplished because its conversion yield usually drops dramatically in the solid state where the low dye mobility inhibits the diffusion controlled mechanisms ruling SUC photophysics. To overcome this limit, we prepared a single‐phase elastomer (poly‐butylacrilate) doped with proper dyes (platinum (II) octaetyl‐porphyrin and 9,10‐diphenylanthracene) to fabricate an efficient photon up‐converting material. Thanks to the residual molecular diffusion provided by the soft host, and to the quenching reduction of involved metastable electronic excited‐states in a solid environment compared to a liquid one, we obtained a record SUC yield of 17% at the solid state. SUC efficiency has been studied as function of the excitation power and sample temperature, elucidating the photophysical processes at the base of the high observed yield and assessing the guidelines for the fabrication of technologically appealing low power up‐converting materials.

The sensitized triplet–triplet annihilation-based upconversion in bicomponent systems is currently considered the most promising strategy for increasing the light-harvesting ability of solar cells. Flexible, manageable, inexpensive up-converting devices become possible by implementing this process in elastomers. Here, we report a study combining optical spectroscopy data of the light conversion process with the nano- and macroscopic viscoelastic characterization of the host material embedding the active dyes, in order to find a rationale for the fabrication of efficient solid-state upconverting systems. By using the poly­(n-alkyl acrylates) as a model of the monophasic elastomers, we demonstrate that the yield of the bimolecular interactions at the base of the upconversion process, namely, energy transfer and triplet–triplet annihilation, is mainly determined by the glass transition temperature (T g) of the polymer. By employing the polyoctyl acrylate (T g = 211 K), we achieved a conversion yield at the solid state larger than 10% at an irradiance of 1 sun, showing the potential of the elastomer-based upconverting materials for developing real-world devices.

Lipocalin-2 (LCN-2) is a 25-kDa secretory protein currently used as a biomarker for renal injury and inflammation. Its source and cause of the increased serum levels are unclear. The current study compares LCN-2 gene expression with known major acute-phase proteins in the liver in a rat and mouse model of turpentine oil-induced sterile abscess. Serum LCN-2 concentrations increased dramatically up to 200-fold (20 μg/mL) at 48 h after turpentine oil injection. A strong elevation of LCN-2 mRNA in rat liver was observed starting from 4 h up to 48 h after injection, with a maximum (8,738 ± 2,104-fold) at 24 h, which was further confirmed by Western blot analysis. In contrast, the increases in gene expression of α₂-macroglobulin, the major acute-phase protein, and hemoxygenase 1, a positive acute-phase protein, were only 1,025 ± 505-fold and 47 ± 12-fold, respectively, during acute-phase reaction (APR). No considerable change was observed in LCN-2 mRNA in rat kidney and other organs as compared with liver. Using wild-type mice, a massive increase in gene expression of LCN-2, with a maximum of 2,498 ± 84-fold in liver, which is similar to that for serum amyloid A (2,825 ± 233-fold), a major mouse acute-phase protein. However, such an increase was significantly inhibited in interleukin 6 knockout mice during APR. Interleukin 6-treated rat hepatocytes induced a significant time-dependent upregulation of LCN-2.Lipocalin-2 is the major acute-phase protein in rat as compared with α₂-macroglobulin and hemoxygenase 1 and comparable with serum amyloid A in mouse whose gene expression is mainly controlled by interleukin 6. The liver is the main source of serum LCN-2 in the case of APR. ABBREVIATIONS-LCN-2-lipocalin-2-α₂M-α₂-macroglobulin-HO-1-hemoxygenase 1-IL-6-interleukin 6-SAA-serum amyloid A-TO-turpentine oil-APR-acute-phase reaction.

Upconversion is a photon-management process especially suited to water-splitting cells that exploit wide-bandgap photocatalysts. Currently, such catalysts cannot utilize 95% of the available solar photons. We demonstrate here that the energy-conversion yield for a standard photocatalytic water-splitting device can be enhanced under solar irradiance by using a low-power upconversion system that recovers part of the unutilized incident sub-bandgap photons. The upconverter is based on a sensitized triplet-triplet annihilation mechanism (sTTA-UC) obtained in a dye-doped elastomer and boosted by a fluorescent nanocrystal/polymer composite that allows for broadband light harvesting. The complementary and tailored optical properties of these materials enable efficient upconversion at subsolar irradiance, allowing the realization of the first prototype water-splitting cell assisted by solid-state upconversion. In our proof-of concept device the increase of the performance is 3.5%, which grows to 6.3% if concentrated sunlight (10 sun) is used. Our experiments show how the sTTA-UC materials can be successfully implemented in technologically relevant devices while matching the strict requirements of clean-energy production.

Photon upconversion based on sensitized triplet−triplet annihilation (sTTA) is considered as a promising strategy for the development of light-managing materials aimed to enhance the performance of solar devices by recovering unused low-energy photons. Here, we demonstrate that, thanks to the fast diffusion of excitons, the creation of triplet pairs in metal−organic framework nanocrystals (nMOFs) with size smaller than the exciton diffusion length implies a 100% TTA yield regardless of the illumination condition. This makes each nMOF a thresholdless, single-unit annihilator. We develop a kinetic model for describing the upconversion dynamics in a nanocrystals ensemble, which allows us to define the threshold excitation intensity I th box required to reach the maximum conversion yield. For materials based on thresholdless annihilators, I th box is determined by the statistical distribution of the excitation energy among nanocrystals. The model is validated by fabricating a nanocomposite material based on nMOFs, which shows efficient upconversion under a few percent of solar irradiance, matching the requirements of real life solar technologies. The statistical analysis reproduces the experimental findings, and represents a general tool for predicting the optimal compromise between dimensions and concentration of nMOFs with a given crystalline structure that minimizes the irradiance at which the system starts to fully operate.