Fluorescence and phosphorescence are two forms of photoluminescence used in modern research and in practical applications. The early observations of these phenomena, before the emergence of quantum ...theory, highlight the investigation into the mechanism of light emission. In contrast to incandescence, photoluminescence does not require high temperatures and does not usually produce noticeable heat. Such a “cold light” was the object of an interesting controversy in the 19th century: does it fit into thermodynamics? The early applications, such as the fluorescent tube, fluorescence analysis, and fluorescent tracers, are described.
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A model for the morphology (size, shape, and crystallinity) of carbon dots (CDs) in the solid state consistent with the observed photoluminescence in solution is proposed herein. Overwhelming ...evidence has been collected that links the data coming from solid‐state analysis (high‐resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry (MS)) to that of solution (pulsed‐field gradient (PFG)‐NMR spectroscopy, time‐resolved fluorescence anisotropy (TRFA), and steady‐state/time‐resolved fluorescence), allowing the establishment of an overall structural model for CDs. According to this model, the so‐called carbon dots, observed under HRTEM imaging, are in fact supramolecular organized structures dynamically assembled from small to medium‐sized molecular species when the solvent is removed to give the solid form. In this way, the imaged nanoparticles (TEM/AFM) are not covalently bound entities formed during the synthetic process, but instead supramolecular entities formed by noncovalent interactions. These particles, if at all present in solution, have the form of loose associations of relatively small molecules. This study was conducted on CDs obtained from the hydrothermal carbonization (HTC) of a biomass waste (olive wet pomace).
A model unraveling the supramolecular nature of the so‐called carbon dots (CDs) is proposed, in which small to medium‐sized molecular species present in dilute solution dynamically assemble into supramolecular organized structures when highly concentrated or in the solid state. (HR‐TEM: high‐resolution transmission electron microscopy, PFG‐NMR: pulsed field gradient‐NMR, TRFA: time‐resolved fluorescence anisotropy).
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An optical dual sensor for oxygen and temperature is presented that is highly oxygen sensitive and covers a broad temperature range. Dual sensing is based on luminescence lifetime measurements. The ...novel sensor contains two luminescent compounds incorporated into polymer films. The temperature-sensitive dye (ruthenium tris-1,10-phenanthroline) has a highly temperature-dependent luminescence and is incorporated in poly(acrylonitrile) to avoid cross-sensitivity to oxygen. Fullerene C70 was used as the oxygen-sensitive probe owing to its strong thermally activated delayed fluorescence at elevated temperatures that is extremely oxygen sensitive. The cross-sensitivity of C70 to temperature is accounted for by means of the temperature sensor. C70 is incorporated into a highly oxygen-permeable polymer, either ethyl cellulose or organosilica. The two luminescent probes have different emission spectra and decay times, and their emissions can be discriminated using both parameters. Spatially resolved sensing is achieved by means of fluorescence lifetime imaging. The response times of the sensor to oxygen are short. The dual sensor exhibits a temperature operation range between at least 0 and 120 °C, and detection limits for oxygen in the ppbv range, operating for oxygen concentrations up to at least 50 ppmv. These ranges outperform all dual oxygen and temperature sensors reported so far. The dual sensor presented in this study is especially appropriate for measurements under extreme conditions such as high temperatures and ultralow oxygen levels. This dual sensor is a key step forward in a number of scientifically or commercially important applications including food packaging, for monitoring of hyperthermophilic microorganisms, in space technology, and safety and security applications in terms of detection of oxygen leaks.
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Here, a comprehensive photophysical investigation of a the emitter molecule DPTZ‐DBTO2, showing thermally activated delayed fluorescence (TADF), with near‐orthogonal electron donor (D) and acceptor ...(A) units is reported. It is shown that DPTZ‐DBTO2 has minimal singlet–triplet energy splitting due to its near‐rigid molecular geometry. However, the electronic coupling between the local triplet (3LE) and the charge transfer states, singlet and triplet, (1CT, 3CT), and the effect of dynamic rocking of the D–A units about the orthogonal geometry are crucial for efficient TADF to be achieved. In solvents with low polarity, the guest emissive singlet 1CT state couples directly to the near‐degenerate 3LE, efficiently harvesting the triplet states by a spin orbit coupling charge transfer mechanism (SOCT). However, in solvents with higher polarity the emissive CT state in DPTZ‐DBTO2 shifts below (the static) 3LE, leading to decreased TADF efficiencies. The relatively large energy difference between the 1CT and 3LE states and the extremely low efficiency of the 1CT to 3CT hyperfine coupling is responsible for the reduction in TADF efficiency. Both the electronic coupling between 1CT and 3LE, and the (dynamic) orientation of the D–A units are thus critical elements that dictate reverse intersystem crossing processes and thus high efficiency in TADF.
The crucial step in the thermally activated delayed fluorescence (TADF) mechanism is the reverse intersystem crossing that converts triplet to singlet states. Here we show that this is mediated by a spin orbit charge transfer (CT) mechanism between the CT manifold and a local triplet state, and requires dynamic rocking about the D‐A bond. This explains how molecular geometry and environment influences TADF and the photophysics of D‐A‐D molecules.
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Invited for the cover of this issue are José Prata and co‐workers at Instituto Superior de Engenharia de Lisboa and Instituto Superior Técnico. The image depicts a model for the supramolecular nature ...of carbon dots. Read the full text of the article at 10.1002/chem.202302955.
“A fundamental… issue is the relationship between carbon dots’ morphological characteristics in the solid state and their photoluminescence both in the solid state and in solution.” This and more about the story behind the front cover can be found in the article at 10.1002/chem.202302955).
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Approximately 10% of patients experience symptoms of Post COVID-19 Condition (PCC) after a SARS-CoV-2 infection. Akin acute COVID-19, PCC may impact a multitude of organs and systems, such as the ...cardiovascular, respiratory, musculoskeletal, and neurological systems. The frequency and associated risk factors of PCC are still unclear among both community and hospital settings in individuals with a history of COVID-19. The LOCUS study was designed to clarify the PCC's burden and associated risk factors. LOCUS is a multi-component study that encompasses three complementary building blocks. The "Cardiovascular and respiratory events following COVID-19" component is set to estimate the incidence of cardiovascular and respiratory events after COVID-19 in eight Portuguese hospitals via electronic health records consultation. The "Physical and mental symptoms following COVID-19" component aims to address the community prevalence of self-reported PCC symptoms through a questionnaire-based approach. Finally, the "Treating and living with Post COVID-19 Condition" component will employ semi-structured interviews and focus groups to characterise reported experiences of using or working in healthcare and community services for the treatment of PCC symptoms. This multi-component study represents an innovative approach to exploring the health consequences of PCC. Its results are expected to provide a key contribution to the optimisation of healthcare services design.
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Einstein's legacy in galaxy surveys Camera, Stefano; Maartens, Roy; Santos, Mário G.
Monthly Notices of the Royal Astronomical Society Letters,
07/2015, Volume:
451, Issue:
1
Journal Article
Peer reviewed
Open access
Non-Gaussianity in the primordial fluctuations that seeded structure formation produces a signal in the galaxy power spectrum on very large scales. This signal contains vital information about the ...primordial Universe, but it is very challenging to extract, because of cosmic variance and large-scale systematics – especially after the Planck experiment has already ruled out a large amplitude for the signal. Whilst cosmic variance and experimental systematics can be alleviated by the multitracer method, we here address another systematic – introduced by not using the correct relativistic analysis of the power spectrum on very large scales. In order to reduce the errors on f
NL, we need to include measurements on the largest possible scales. Failure to include the relativistic effects on these scales can introduce significant bias in the best-fit value of f
NL from future galaxy surveys.
A new diethylenetriamine-derived macrocycle known as L, bearing 2-methylquinoline arms and containing m-xylyl spacers, was prepared in good yield by a one-pot 2 + 2 Schiff base condensation ...procedure, followed by reduction with sodium borohydride. Up to now this is the first hexaazamacrocycle with appended fluorophore units. Single-crystal X-ray diffraction determination of the dinuclear zinc(II) complex of L showed that metal centers are located at about 7.20(2) Å from one another. This complex exhibits only weak fluorescence in aqueous solution, but the addition of 1 equiv of pyrophosphate (PPi) caused a 21-fold enhancement of the fluorescence intensity. The sensor response is linear up to a value of 10 μM HPPi3– and has a detection limit of 300 nM. The receptor behaves as a highly selective sensor for pyrophosphate as other anions, including phosphate, phenylphosphate (PhP), adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP), failed to induce any fluorescence change and practically do not affect the fluorescence intensity of the sensor in the presence of HPPi3–. Competition titrations carried out in aqueous solution at pH 7.4 in 20 mM 3-(N-morpholino)propanesulfonic acid (MOPS) buffer by spectrofluorometry revealed a high association constant value of 6.22 log units for binding of PPi by the dinuclear zinc(II) receptor, one of the highest reported values for colorimetric/fluorometric sensors able to work under real aqueous physiological conditions, while association constant values for binding of the other phosphorylated substrates are in the 5.51–4.03 log unit range.
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10.
Machining of aluminum alloys: a review Santos, Mário C.; Machado, Alisson R.; Sales, Wisley F. ...
International journal of advanced manufacturing technology,
10/2016, Volume:
86, Issue:
9-12
Journal Article
Peer reviewed
The use of aluminum alloys in manufacturing industry has increased significantly in recent years. This is because primarily to their ability to combine lightness and strength in a single material. ...Concomitant to this growth, the machining of aluminum alloys has enormously increased in volumetric proportions—so that the chip volume represents up to 80 % of the original volume of the machined material in certain segments of the industry, like aerospace. In this context, knowledge of the characteristics of machinability of aluminum alloys is essential to provide industry and researchers with information that allows them to make the right decisions when they come to machining this fantastic material. The purpose of this review is to compile relevant information about the characteristics of machinability of aluminum alloys into a single document.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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