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Irradiation with intense blue LED light of Lumogen orange 240 (1) in non-reactive solvents led to bleaching. The products of these photochemical reactions were not possible to determine. Contrarily, irradiation in ethanol or propanol led to red color shifts caused by the formation of the ethoxy or propoxy derivative of Lumogen orange 240, respectively. These new reaction products are only formed when both light and oxygen are present. A possible mechanism for these photo-oxidation reactions, the implication for the stability of perylene type of fluorescent dyes under LED lamp conditions and possible preparative applications are discussed.

Photochemical stability and possible routes for photodegradation of twisted diarylnitroxides were determined. It was shown that quantum yields for twisted diarylnitroxides fall in the range typical for the best representatives of alkylnitroxides providing an additional support that twisting of the phenyl ring from the N-O conjugation plane constitutes an efficient route for increasing thermo and photo stability of the nitroxides.

Stability studies of two avobenzone transformation products: chloro-avobenzone [2-chloro-1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione] and dichloro-avobenzone [2,2-dichloro-1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione] have been performed at different pHs values as well as under UV A light and compared with the stability of avobenzone, one of the mostly used UV A filter present in sunscreens. We have additionally investigated the possibility of application of TiO2 photocatalysis as a method for the removal of them. Results have shown the differences in pH stability of all three studied compounds with much slower degradation rate under neutral conditions in comparison to the acidic ones for all three studied compounds. In the case of photolytic experiment, performed under UV A light, dichloro-avobenzone exhibited the lowest UVA stability (half-life 22.4 ± 0.7 min), while avobenzone and chloro-avobenzone are much more stable and have shown quite similar degradation pattern (half-lives 126 ± 16 min and 128 ± 25 min). Under the photocatalytic conditions the less stable was dichloro-avobenzone (half-life 14.1 ± 0.6 min), while chloro-avobenzone and avobenzone were much more stable (half-lives 41 ± 3 min and 79 ± 13 min). Dichloroavobenzone is significantly more reactive than avobenzone and its monochloro-derivative. On the basis of the formation of various stable degradation products, including substituted acetophenones, benzoic acids and phenols, identified by GC-MS, the degradation pathway has been proposed.

Novel two fluorescein derivative dyes, 2-(6-Hydroxy-3-oxo-3H-xanthen-9-yl)-N-(2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)benzoyl)-N-(2-hydroxyphenyl)benzamide (o-OHAnF) and 2-(6-Hydroxy-3-oxo-3H-xanthen-9-yl)-N-(2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)benzoyl)-N-(4-hydroxyphenyl)benzamide (p-OHAnF) had been synthesized. Optical properties and photo-physical parameters in different pH media and solvents were studied. o-OHAnF and p-OHAnF showed extra prototropic forms with absence of lactonic form which present as neutral prototropic form (causing − ve effect on optical properties) in case of fluorescein dye. Their amplified spontaneous emission (ASE) efficiencies were examined as function of dye concentrations. Photo-stability behavior of the new dyes was extremely different than the parent standard fluorescein dye.

Electro-fluidic display (EFD) is one of the most promising reflective displays because of its full color and video speed. Colored EFD oil, which normally consists of soluble organic dyes and non-polar solvent, plays a critical role in color, electro-optical behavior, and the reliability of the EFD devices. In this paper, we report our research on two kinds of electro-fluidic dyes based on anthraquinone and azo pyrazolone, including their synthesis, structure characterization, and application properties. Changes of absorbance curves, color coordinates of oils, and photoelectric responses of devices were studied in detail under accelerated irradiation to investigate the photo-stability and reliability properties of synthesized oil materials and devices. Photoelectric responses and photo stability of dyes are highly varied depending on their structures. We found that 1,4-dlialkylamino anthraqinone and mono azo pyrazolone dyes are much more stable than 1,8-dlialkylamino anthraqinone and corresponding bisazo pyrazolone dyes.

Sunscreen products are mostly used to protect human skin from adverse effects of ultra-violet light like DNA damage, photo-aging and sunburns. Photo-stability is one of the critical requirements for an effective sunscreen. However, most commercially available sunscreen compounds exhibit photo-reactions leading to formation of harmful products. The objective of the current research was to investigate the photo-chemical and photo-physical properties of few selected sunscreens formulations and also to explore photo-stability and photo-sensitizing properties of few selected organic UV filters used in the sunscreens. Photo-degradation mechanisms of the selected sunscreens ingredients were analysed using time-resolved Laser Flash Photolysis and steady-state HPLC coupled with Mass Spectrometry. Oxybenzone (OXB) was revealed to be a sufficiently stable UV filter even after 24 h of radiation exposure, whereas, Avobenzone (AVOB) and Ecamsule (ECAM) were found to be a photo-unstable sunscreen.

Hair color change by dye application is a common procedure among women. Hair dyes are classified, according to color resistance, into temporary, semipermanent, demipermanent and permanent. The first two are based on molecules which are already colored. Temporary dyes act through dye deposition on cuticles, but semipermanent may penetrate a little into the cortex and so the color resists up to six washes. Demipermanent and permanent dyes are based on color precursors, called oxidation dyes, and the final shade is developed by their interactions with an oxidizing agent, but they differ from the alkalizing agent used. In oxidation systems, there is an intense diffusion of the molecules into the cortex, what promotes a longer color resistance. Dyes and color precursors present differences related to chromophore groups, hair fiber affinity, water solubility, and photo stability. The aim of this review is to discuss the differences among hair dye products available in the market and their action mechanisms, molecular structures, application methods, and some aspects of formulations.

A route to fabricate the homogeneous one-dimensional (1D) Ni x Cd1−x S nanorods (NRs) photocatalysts is designed with ethanediamine-assisted decomposition of Ni x Cd1−x (DDTC)2 complex precursors. This route developed Ni x Cd1−x (DDTC)2 complex precursors by co-precipitation method at room temperature condition. The effects of Ni2+ doped into CdS lattice on the length and photocatalytic performance of the Ni x Cd1−x S NRs have been investigated in detail. It is found that doping of Ni2+ significantly affects the aspect ratio of 1D Ni x Cd1−x S NRs. With the increasing doping concentration of Ni2+, the length of as-obtained Ni x Cd1−x S NRs becomes shorter. In addition, their photocatalytic activity was evaluated by the degradation of Rhodamine B dye as a probe reaction under visible-light irradiation. The results show that the optimal Ni2+ addition shows efficient photocatalytic performance and excellent photo stability, which may result from Ni2+ lattice doping. A tentative photocatalytic mechanism of 1D Ni x Cd1−x S NRs is proposed for further explanation of photocatalytic performance.

Solution-processed organic small molecule solar cells (SMSCs) have achieved efficiency over 11%. However, very few studies have focused on their stability under illumination and the origin of the degradation during the so-called burn-in period. Here, we studied the burn-in period of a solution-processed SMSC using benzodithiophene terthiophene rhodamine:[6,6]-phenyl C71 butyric acid methyl ester (BTR:PC71BM) with increasing solvent vapour annealing time applied to the active layer, controlling the crystallisation of the BTR phase. We find that the burn-in behaviour is strongly correlated to the crystallinity of BTR. To look at the possible degradation mechanisms, we studied the fresh and photo-aged blend films with grazing incidence X-ray diffraction, UV–vis absorbance, Raman spectroscopy and photoluminescence (PL) spectroscopy. Although the crystallinity of BTR affects the performance drop during the burn-in period, the degradation is found not to originate from the crystallinity changes of the BTR phase, but correlates with changes in molecular conformation – rotation of the thiophene side chains, as resolved by Raman spectroscopy which could be correlated to slight photobleaching and changes in PL spectra.

To inquire into the role of the carboxyl group as determinant of the properties of 5,6-dihydroxyindole melanins, melanins from aerial oxidation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and its DHICA methyl ester (MeDHICA) were comparatively tested for their antioxidant activity. MALDI MS spectrometry analysis of MeDHICA melanin provided evidence for a collection of intact oligomers. EPR analysis showed g-values almost identical and signal amplitudes (DeltaB) comparable to those of DHICA melanin, but spin density was one order of magnitude higher, with a different response to pH changes. Antioxidant assays were performed, and a model of lipid peroxidation was used to compare the protective effects of the melanins. In all cases, MeDHICA melanin performed better than DHICA melanin. This capacity was substantially maintained following exposure to air in aqueous buffer over 1week or to solar simulator over 3hr. Different from DHICA melanin, MeDHICA melanin was proved to be fairly soluble in different water-miscible organic solvents, suggesting its use in dermocosmetic applications.

Bisindeno-annulated pentacenes 3a and 3b were synthesized by a simple regio-selective, FeCl3-mediated Scholl reaction from the corresponding 6,13-diaryl pentacene precursors. The fusion of two indeno-units dramatically changes the electronic properties and chemical reactivity of pentacene and the obtained compounds exhibited exceptionally high photo-stability in the solution, with a half-life time of 11.2 (3a) and 32.0 (3b) days under ambient light and air conditions. Ordered molecular packing with a small π-π stacking distance was observed in the single crystals of 3a and 3b. Our research provides a promising strategy to access stable higher order acenes with controlled molecular order.

The demand for bioactive molecules, such as β-carotene (β-car), has increased, but some characteristics such as low water solubility and low photo stability limit its application in many formulations. The bioactive entrapment into milk proteins may overcome this barrier. Thus, the aim of this work was to study the interaction between β-car and bovine serum albumin (BSA) or β-casein and the photo stability of this bioactive in the presence of the proteins. Fluorescence spectroscopy showed that at pH 7.0, increasing concentrations of β-carotene reduced the fluorescence intensity of both proteins, and the fluorescence-quenching mechanism is mainly static. The stoichiometry of the β-car/protein complex varied between proteins, being 1:1 to native BSA, 1:3 to denatured BSA (d-BSA), and 1:2 for β-casein. The standard Gibbs-free energy (ΔG°) of complex formation was negative for all systems studied and followed the order ΔG°BSA

Irradiation of Lumogen Red 305 (3) in ethyl acetate with intense blue LED light led to very slow bleaching, showing a high photochemical stability. However, irradiation in ethanol led to the formation of a low yield product in which one of the phenoxy groups is substituted by an acetoxy group, the oxidized form of an ethoxy group. This reaction product was only formed in the presence of blue light and oxygen. Adding a small amount of acetic acid to the solutions resulted in a much higher yield of the product, indicating a possible photo oxidation of ethanol to acetic acid during the process in this solvent. A similar dye (5) containing less phenoxy side groups than Lumogen Red 305 showed the same reaction although the product formed showed lower chemical stability. The photo-substitution of phenoxy groups by acetoxy groups is a new reaction. The results are used to discuss the structural effects on the stability of these type of fluorescent dyes under irradiation conditions, potential reaction mechanisms and the possibility of using the photochemical transformations for preparative purposes.

The factors that influence the photo-stability of Ag@AgBr plasmonic photocatalyst, such as light resource, electron/hole quencher, dye sensitizer, and atmosphere environment, were investigated in detail. It was revealed that Ag@AgBr can remain stable under weak light sources while it will become unstable under strong light sources. Electron quenchers are favorable to improving the stability of Ag@AgBr while hole quenchers do the opposite. Acting as a sensitizer, acid orange 7 dye is detrimental to the stability of Ag@AgBr. As for the atmospheric environment, air and oxygen-rich atmospheres are more favorable for keeping the stability of Ag@AgBr than vacuum atmosphere.

CdS-capped CdSe nanocrystals (NCs) which show high luminescence quantum yield are synthesized without any Poisonous Materials in aqueous solution. The synthesis in an aqueous medium without any poisonous materials is attached importance to. The absorption spectroscopy and photoluminescence spectroscopy are employed to analyze the NCs. It takes 78s that the intensity decreases to the half for bare CdSe NCs, but 442s for CdSe/CdS core/shell NCs. The photo stability of CdSe NCs under 325nm laser irradiation is enhanced greatly after CdS overcoating.

The use of trans-resveratrol in medicine has limitations due to its low stability and toxicity at higher doses of administration. In order to overcome these problems, the inclusion complexes with trans-resveratrol are prepared. However, it is necessary to investigate the stability of the substance before the preparation of the complexes. Therefore, the aim of this study was to study a photo and thermal stability of trans-resveratrol. In order to investigate the photostability of trans-resveratrol, a sample was irradiated in a photochemical reactor with lamps of the appropriate wavelength. The obtained changes in the structure of trans-resveratrol after the effect of radiation were monitored using UV-VIS method. Thermostability of trans-resveratrol without the effect of solvents was investigated using infrared spectroscopy in the temperature range of 25-250°C. The content of trans-resveratrol was decreased up to 45.09% after 300 min of UVA irradiation, i.e. up to 37.55% after UVB irradiation. The results indicate that trans-resveratrol is sensitive to the effect of UV radiation. Based on the thermostability study, it was found that trans-resveratrol is a thermostable substance in the investigated temperature range.

We have investigated the photo-stability of pristine and super-hydrogenated pyrene cations C$_{16}$H$_{10+m}^+, m = 0,6, \mathrm{\ or\ } 16$) by means of gas-phase action spectroscopy. Optical absorption spectra and photo-induced dissociation mass spectra are presented. By measuring the yield of mass-selected photo-fragment ions as a function of laser pulse intensity, the number of photons (and hence the energy) needed for fragmentation of the carbon backbone was determined. Backbone fragmentation of pristine pyrene ions (C$_{16}$H$_{10}^+$) requires absorption of three photons of energy just below 3 eV, whereas super-hydrogenated hexahydropyrene (C$_{16}$H$_{16}^+$) must absorb two such photons and fully hydrogenated hexadecahydropyrene (C$_{16}$H$_{26}^+$) only a single photon. These results are consistent with previously reported dissociation energies for these ions. Our experiments clearly demonstrate that the increased heat capacity from the additional hydrogen atoms does not compensate for the weakening of the carbon backbone when pyrene is hydrogenated. In photodissociation regions, super-hydrogenated Polycyclic Aromatic Hydrocarbons (PAHs) have been proposed to serve as catalysts for H$_2$-formation. Our results indicate that carbon backbone fragmentation may be a serious competitor to H$_2$-formation at least for small hydrogenated PAHs like pyrene., 6 pages, 4 figures, accepted in The Astrophysical Journal

There is still an international need to develop broad-spectrum sunscreen products with an adequate UVB/UVA balance, while the approved filters available in the UVA are scarce. Currently, one of the few UVA filters approved in the United States and Europe is tert-butylmethoxydibenzoylmethane (BMDM, avobenzone). However, this compound is unstable from aphotochemical point of view and cannot be used in combination with certain sunscreens. In this paper, we investigate the photochemical behavior of a set of dibenzoylmethanes and chalcones. In particular, we carry out their absorption and emission spectra, evaluate their photochemical degradation, and study their generation of free radicals and singlet oxygen photoproduction. Two compounds resultedin having the basic properties of UVA filters (2′-hydroxy-4-methoxychalcone and 2′-hydroxy-4-methoxydibenzoylmethane). Further studies are proposed, such asformulating the compoundsinto emulsions or other commoncosmetic presentations, as well as combining them with broadly-used UVB filters. We have also considered the need to establish its toxicological profile.

Fluorescence intensity traces of single dibenzoterrylene molecules in 2,3-dimethylnaphthalene crystals were studied at 270 K. It was found that these molecules are considerably more photo-stable than those of terrylene in the same crystal. Quantum-chemical calculations indicated that the creation of the reactive singlet oxygen state via the triplet state is not probable for dibenzoterrylene, in contrast to terrylene. This reaction provides the first step in typical hydrocarbon oxidation. Therefore, the lack of the triplet channel in the case of dibenzoterrylene, and its domination in the photo-oxidation of terrylene, may explain the different photo-stability of the two compounds.

Novel, squarylium dyes containing 1-(alkylcarbamoylmethyl)-2,3,3-trimethyl- 3 H -indolium groups were synthesized and their UV/Vis and fluorescence spectra, aggregation, photo-stability and association with bovine serum albumin were studied. The absorption and emission max wavelengths of the dyes in different solvents were in the range 619–653 nm. Compared to a typical ethyl squarylium dye, the introduction of alkylcarbamoylmethyl groups reduced aggregation and improved molar extinction coefficient, fluorescence quantum yield and photo-stability in water. Moreover, the fluorescence intensity of the dyes increased upon the addition of BSA in pH 7.0 phosphate buffer solution. An excellent linear relationship ( r 2 = 0.9982) was obtained between fluorescence intensity and bovine serum albumin concentration.

Novel, zinc (II) phthalocyanines substituted with 2-adamantanol and 1-adamantanethiol moieties were prepared from the corresponding phthalonitriles employing commercially available 3- and 4-nitrophthalonitrile as the starting material. The Q-band of tetra-α-substituted phthalocyanines occurred at longer wavelengths than those of the corresponding, tetra-β-substituted phthalocyanines. Substituents at the β position increased ΦF values; all phthalocyanines studied displayed excellent singlet oxygen generations ability, with α-substituted dyes showing higher ΦΔ values than their β-isomers. The dyes exhibited good photo-stability, with α-substituted phthalocyanines proving to be of higher stability than the corresponding β-isomers.

Fluorescence excitation spectra and fluorescence intensity traces of single terrylene molecules in 2,3-dimethylnaphthalene crystals were studied at 5 K and also at temperatures between 200 and 290 K. Terrylene molecules were found to be relatively photo-stable in crystals obtained by cosublimation of both components under an argon atmosphere whereas these molecules were more easily photo-bleached in crystals obtained under a helium atmosphere. It is propose that the diverse behaviour in both groups of crystals is due to different penetration by oxygen and bleaching of terrylene molecules by photo-oxidation. The fully saturated fluorescence detection rates for the (0, 0) and vibronic transitions were studied.

Background Nanoparticles (NPs) are increasingly being used in a number of applications that include biomedicine, biological labeling and cancer marker targeting, and their successful storage is important to preserve their viability. A systematic investigation of the thermal and photo stability of chemically stabilized cadmium telluride (CdTe) quantum dots (QDs) under various storage conditions either in solution or as dried nanoparticles has not been published. Here we report experiments involving chemically synthesized glutathione-capped CdTe QDs whose photoluminescence spectra were examined initially and then periodically during storage times up to 76 days. Methods Samples of dried QDs or QDs in solution (water or buffered) were examined under different light conditions including complete darkness, constant 12,000 lux incident light, and under diurnal sunlight; at temperatures ranging from -80°C to room temperature. Results Though QDs stored in solution in the dark at -80°C lost only 50% of peak fluorescence (FL510) within 2 weeks, solution-stored QDs exposed to sunlight at room temperature showed FL510 drops of 85% in the first 24 hours. In contrast, QDs precipitated from aqueous solution, dried and stored in time course experiments in the presence of atmospheric oxygen – when resuspended in water – lost an average of only 12% FL510 over 76 days under all conditions tested, even in direct sunlight. Conclusions Glutathione-capped CdTe particles can be stored as dried nanoparticles for extended periods of time, enhancing their viability in biomedicine, biological labeling and cancer marker targeting.

In this paper, a new kind of nonlinear optical chromophores containing thiophene 1,1-dioxides subunit was designed and theoretically studied. It has been found that this kind of nonlinear optical chromophores has higher second-order polarizabilities and better thermal and photo stability than their thiophene precursors. Thus they are good candidates for application in electrooptical device.

Polymerization of methyimethacrylate (MMA) in the presence of eight benzanthrone dyes, five of them containing an unsaturated group, was investigated. Some spectroscopic characteristics of tour of the dyes were determined. It was established that photo stability of the dyes increased significantly when they were either chemically bonded in polymer molecules or in the mass of the polymer. The influence of the dyes-containing unsaturated group, on the rate of the copolymerization was determined. The influence of all eight dyes on the photo stability of the coloured polymers, obtained in their presence, was established.

Photo-degradation, thermal-degradation and aqueous-instability of indocyanine green (ICG) limits its application as a fluorescence contrast agent for imaging purposes. Thus, the objective of this study is to develop polymeric nanoparticles entrapping ICG and to establish its effectiveness in providing photo-stability, thermal stability and aqueous stability to ICG. Nanoparticles entrapping ICG were engineered, characterized and the degradation kinetics of ICG in the nanoparticles was investigated in aqueous media. The entrapment of ICG in the nanoparticles causes a shift in its wavelength of peak fluorescence and a decrease in its peak fluorescence intensity. The degradation of ICG in aqueous nanoparticle suspension followed first-order kinetics for the time period studied. ICG entrapment in the nanoparticles enhanced aqueous-stability of ICG (half-life, t(1/2) was 72.2+/-6.1 h for ICG in the nanoparticles as compared to 16.8+/-1.5 h for free ICG solution), photo-stability of ICG (t(1/2) was 73.7+/-7.5 h for ICG in the nanoparticles as compared to 14.4+/-2.4 h for free ICG solution when exposed to room light from two 32 W normal fluorescent tubes) and thermal-stability of ICG (t(1/2) of ICG at 42 degrees C was 62.4+/-1.7 h for ICG in the nanoparticles as compared to 10.1+/-0.6 h for free ICG solution).

2- Iso -propylthioxanthone (ITX) and N -methyldiethanolamine (MDEOA) were used as the initiating system to study the photo-chemical stability of photo-cured coatings. Primary yellowing is caused by photo-products from initiator residues. This yellowing decreases during storage in darkness. Permanent yellowing is caused by photo-degradation of the resin used. This photo-degradation is sensitized by ITX. Photo-curing in the presence of oxygen leads to a rapid surface oxidation. Photo-oxidation studies with ESCA, infra-red reflection and transmission spectroscopy show that the oxidation occurs mainly in a thin surface layer. In a surface layer ∼ 10 nm thick, oxidation is almost complete after 24–48 hours' ageing.

A review of physical, chemical, analytical and pharmacological properties of nitroprusside is presented. In view of the pharmaceutical applications of nitroprusside special attention is given to the discussion of the (photo)degradation, the stability of the pharmaceutical formulations, the application as a reagent in pharmaceutical analysis and the redox behaviour.