1,721,016 research outputs found
Accurate Analysis of Spectrophotometric Data to Quantify the Photoswitching Performance of a Biomimetic E/Z Light-Induced Molecular Switch
No full textPhotoswitches are widely investigated molecules because upon exposure to selected light irradiation, they are able to undergo structural, and hence optical, changes. To fully exploit their responsiveness to irradiation, the quantum efficiency of the forward and back reactions is a fundamental parameter, whose accurate determination is critical. In this work, the spectral evolution of a biomimetic switch, which undergoes E/Z photoinduced isomerization, is spectrophotometrically examined. The minimal spectral differences between the E and Z forms inhibit the accurate determination of the quantum efficiency of the E-Z and Z-E photoconversions. We present a kinetic analysis of the E-Z spectral evolution, which enables us to determine quantum yields of the forward and back reactions; the data show that the back reaction has a higher efficiency (0.60) than the forward process (0.49), evidencing that irradiation conditions have to be carefully selected to accumulate the Z isomer. The method has been further used to determine the E-Z and Z-E quantum yield in the deprotonated form of the biomimetic switch; the obtained values demonstrate that under basic conditions, the back reaction is relatively more efficient than the forward one even for the deprotonated species. The detailed analysis enables us to establish the conditions to monitor the fluorescence of the E and Z forms, setting the basis for a more sensitive detection of the photoswitch and its transformation
Effects of glutathione on the luminescent behavior of CdSe-nanocrystals
No full textThe luminescent behavior of semiconductor nanocrystals is a sensitive reporter of their electronic properties and of the impact of surface passivation on the excitonic state. In this work, CdSe nanocrystals (CdSe-Nc) are prepared in microemulsions and the effects of tripeptide Glutathione (GSH) as a stabilizing ligand, are examined. The CdSe samples are investigated by steady-state and time-resolved luminescence methods. The luminescent properties of CdSe without GSH spectrally evolve over time, and a dramatic reduction of luminescence intensity and decay times are observed. This behavior suggests that although the colloids are in microemulsion media, they undergo progressive aging that ruins their luminescent properties. The presence of GSH in the microemulsions at the beginning of the synthesis stops the nanocrystal aging, thus acting as an efficient stabilizing agent, freezing the luminescence properties of CdSe nanocrystals. The effects of GSH on the colloids are also documented by a detailed analysis of luminescence decay times, carried out through the Maximum Entropy Method. Interestingly, the addition of GSH on aged CdSe colloids is able to not only stabilize the structures but also recover the luminescent efficiency leading to an attractive “brightening” effect
Photoinduced substitution reactions in halothiophene derivatives. Steady state and laser flash photolytic studies
No full textSolvent dependent iodide oxidation in metal-halide perovskite precursor solutions
No full textSolar cell absorbing layers made of metal-halide perovskites (MHPs) are usually deposited from solution phase precursors, which is one of the reasons why these materials received huge research attention in the last few years. A detailed knowledge of the solution chemistry is critical to understand the formation of MHP thin films and thus to control their optoelectronic properties and the reproducibility issues that usually affect their synthesis. In this regard, the concentration of triiodide, I-3(-), is one factor known to have an influence on regulating important aspects such as the particle size in the solution and the defect concentration in the film. In this study, we highlight an underestimated source of I-3(-), namely the iodide salt solutions ubiquitously employed in MHP synthetic routes, which not only lead to the formation of I-3(-) but also detracts available I- for the MHP synthesis, thus establishing under-stoichiometric conditions. Particularly, we show how the oxidation of I- to I-3(-) changes in time with both the iodide salt counter-cation (K+, CH3NH3+) and the used solvent, meaning that variable quantities of I-3(-) are found depending on the synthesis conditions, with enhanced oxidation found in the gamma-butyrolactone (GBL) solvent. Though these differences are generally small, we shed light on a hidden and ever-present reaction which is likely to be related to the overall processing quality of MHP thin films
The effect of pH and ionic strength on the fluorescence properties of a red emissive DNA-stabilized silver nanocluster
No full textDNA-stabilized silver nanoclusters (DNA-AgNCs) are a class of promising fluorophores for imaging and sensing applications. All aspects of their spectroscopic properties are not yet fully characterized, leaving this field still with a number of fundamental studies to be addressed. In this work, we studied the spectroscopic properties of red-emitting DNA-AgNCs at different pH (5 to 9) and ionic strength μ (0.005 to 0.5). The photophysical properties of high performance liquid chromatography (HPLC) purified DNA-AgNCs proved to be constant over a large range of pH and μ, with absorption, emission and fluorescence decay times only being affected at very high pH and μ values. Non-purified DNA-AgNCs were also unaffected by pH and/or μ variations, but significant differences can be observed between the rotational correlation times of purified and non-purified DNA-AgNCs
UV-Visible radiation modulation abilities of photon up-converting nanocapsules integrated with an oscillatory reaction
No full textRadiation up-conversion through the triplet-triplet annihilation mechanism has been widely studied, mostly in solution and under de-aerated conditions. We propose oil-in-silica up-converting nanocapsules resulting in a robust solid-like material able to generate blue up-converted emission and preserve the red phosphorescence of the sensitizer under atmospheric conditions. The core phase consists of oleic acid containing the up-converting molecular pair, platinum octa-ethyl-porphyrin and 9,10-diphenyl-anthracene; the silica shell having 10-15 nm thickness acts as a protective barrier and compartmentalizes the organic molecules. The up-converted emission is measured from silica nanocapsule powder or in aqueous suspensions using an incoherent and low power density (363 μW cm−2) source. The robustness of the oil-in-silica structures is tested in the acidic and oxidative solution of the oscillatory Belousov-Zhabotinsky (BZ) reaction. The BZ reaction gives rise to a modulated optical density in the UV-region. The modulated UV radiation is absorbed by the chromophores in the nanocapsules delivering periodic emissions of the capsules, which are monitored in terms of intensity amplitude and periodicity. The solidness of the nanocapsules enables employing them in a wet chemical formulation to be exposed simultaneously to the BZ-modulated UV radiation and to the steady-state Vis radiation, obtaining multiple output luminescence signals. Furthermore, the impact of simultaneous excitations empowers discussions of the intensity changes in terms of efficiencies of triplet energy transfer and establishing UC-nanostructured materials for optical communication applications
Metal Nanoparticles Catalyzed C-C Bond Formation via C-H Activation
No full textThis chapter will discuss the rationale, design, and choice of metal nanoparticles as active catalysts for C-C bond formation via C-H activation to highlight their relevance in the determination of reaction parameters. Zerovalents, oxides, and bimetallic metals in nanocatalysis will be considered. Significant experiments into mechanism comprehension will be examined in relevant key examples. This chapter includes literature present on this topic through March 2020
Photoinduced substitution reaction in halothiophenes. quantum-mechanical and photochemical studies on nitro- and cyano-derivatives
No full textSolid state photoreduction of silver on mesoporous silica to enhance antifungal activity
Full text linkA solid-state Ultraviolet-photoreduction process of silver cations to produce Ag0 nanostructures on a mesoporous silica is presented as an innovative method for the preparation of efficient environmental anti-fouling agents. Mesoporous silica powder, contacted with AgNO3, is irradiated at 366 nm, where silica surface defects absorb. The detailed characterization of the materials enables us to document the silica assisted photo-reduction. The appearance of a Visible (Vis) band centered at 470 nm in the extinction spectra, due to the surface plasmon resonance of Ag0 nanostructures, and the morphology changes observed in transmission electron microscopy (TEM) images, associated with the increase of Ag/O ratio in energy dispersive X-ray (EDX) analysis, indicate the photo-induced formation of Ag0. The data demonstrate that the photo-induced reduction of silver cation occurs in the solid state and takes place through the activation of silica defects. The activation of the materials after UV-processing is then tested, evaluating their antimicrobial activity using an environmental filamentous fungus, Aspergillus niger. The treatment doubled inhibitory capacity in terms of minimal inhibitory concentration (MIC) and biofilm growth. The antimicrobial properties of silver–silica nanocomposites are investigated when dispersed in a commercial sealant; the nanocomposites show excellent dispersion in the silicon and improve its anti-fouling capacity
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