The effect of substituent groups in bis(dithiobenzil) nickel compounds on their absorption spectra,reduction potential and singlet oxygen quenching efficiency

The influence of substituents on the longest wavelength (Λ_max) of absorption maxima and the reduction potential of bis(p-substituted dithiobenzil) nickel compounds has been evaluated by the classical Hammett equation. A good linear relationship between Λ_max or reduction potential and σ_p or σ_p⁺ shows that at least one phenyl ring is conjugated with the five-membered nickel chelate ring, although neither of the phenyl rings is actually coplanar to the chelate ring. The amount of singlet oxygen quenched by bis(p-substituted dithiobenzil) nickel has been conveniently measured by means of a gas chromatograph using a capillary column.     

Photo-oxidative degradation of nylon 66 under accelerated weathering

The photo-oxidative degradation study of nylon 66 was carried out in a polychromatic irradiation chamber (Sepap 12/24, λ≥290 nm) at 60°C in air. The extent of photo-oxidation was monitored by Fourier transform infrared spectrometry. The sample underwent extensive changes in hydroxyl, carbonyl and amorphous region of infrared upon irradiations. The photo-products were characterized by i.r. and ultraviolet spectroscopy. The broadening of hydroxyl and carbonyl absorption bands indicated more than one species. The photo-oxidation mechanism implies the same intermediate photo-products. The kinetics of the photo-degradation also has been studied.     

Improvement in the light fastness properties of dyed and pigmented materials. 1-The effect of antioxidants on the photostabilisation of dyes in cellulose acetate film

The effect of some added antioxidants on the photodegradation of C.I. Solvent Yellow 33 (quinophthalone) and C.I. Direct Red 39 in cellulose acetate films have been investigated. The effects varied according to antioxidant type. For example, the addition of 2, 6-di-t-butyl-4-methylphenol, an effective radical scavenger, afforded little protection against photodegradation, while singlet oxygen quenching of antioxidants such as nickel bis(dithiobenzil), nickel dialkyldithiocarbamate, nickel bis(mesitylenesulphonate) conferred improved resistance of the dyes towards photodegradation.     

Studies on photodegradation of poly(vinyl chloride), part 3

PVC films were degraded by outdoor exposure, irradiation by a weatherometer and heating by an electric oven. In PVC films subjected to outdoor exposure and to irradiation by the weatherometer at a low temperature, e. g. sample surface temperature of 0°C, photo-oxidation and scission of the main chain were caused, but dehydrochlorination or formation of solvent-insoluble substances were not observed. In contrast, PVC subjected to irradiation by the weatherometer at a high temperature, e. g. sample surface temperature of 80°C, showed a degradation tendency similar to that of PVC heated at 200°C in the electric oven, and decomposition of the thermal degradation type characterized by dehydrochlorination, formation of polyenes and formation of solvent-insoluble substances were observed.     

Photo-oxidation mechanisms of poly(2,6-dimethyl-1,4-phenylene oxide).

A re-examination of the photo-oxidation mechanism of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at both long and short irradiation wavelengths under accelerated conditions is reported. The formation rate of poly-2,6-dimethylphenoxy (PDMP) radicals, have been observed by esr spectroscopy, while benzylic-type radicals have been detected by spin trapping experiments using nitrosodurene under UV irradiation conditions. The changes of FTIR spectra obtained under accelerated photo-oxidative conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical cations and superoxide anions by a photo-induced electron-transfer reaction is suggested under our conditions. In addition, some results on the of photo-oxidation PPO/PS blends as a function of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend containing atactic polystyrene. This effect has been ascribed to the absence of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO with bromine gave a bromomethylated PPO with different amounts of CH₂ Br groups, which has been used for further substitution reactions with alkoxy sodium salts of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMPP). The accelerated photo-oxidation of a modified copolymer PPO-PMPP containing a 60% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a commercially available hindered amine light stabilizers (HALS) and a modified copolymer PPO-PMPP are also reported under the same photo-oxidative conditions.     

Surface functionalization of multiwalled carbon nanotubes with UV and vacuum UV photo-oxidation

Multiwalled carbon nanotubes (MWNTs) were surface photo-oxidized at room temperature with UV (253.7 and 184.9 nm) and vacuum UV (VUV) (106.7 and 104.8 nm) radiation. X-ray photoelectron spectroscopy (XPS) showed rapid UV photo-oxidation during the first hour of treatment and then an increase that was directly proportional to the time of treatment up to 4 h where the oxygen concentration was 7.5 at%. VUV photo-oxidation resulted in an oxygen concentration up to 9.5 at% with exposure time for the initial 2 h of treatment. Beyond 2 h, the oxygen concentration decreased with exposure to VUV photo-oxidation. Curve fitting of the XPS C_1s spectra revealed mainly C–O–C, as ether or epoxy functional groups, with the presence of C=O, O–C=O and O=C–O–C=O or carbonate moieties. SEM micrographs showed no apparent effect on the structure or appearance of the MWNTs as expected from surface modification. Gas-phase UV and VUV photo-oxidation effectively functionalize MWNTs for potential adhesion improvement without resulting in liquid waste as from the traditional bulk processing method involving acidic oxidation.     

Free Radicals and ROS Induce Protein Denaturation by UV Photostability Assay

Oxidative stress, photo-oxidation, and photosensitizers are activated by UV irradiation and are affecting the photo-stability of proteins. Understanding the mechanisms that govern protein photo-stability is essential for its control enabling enhancement or reduction. Currently, two major mechanisms for protein denaturation induced by UV irradiation are available: one generated by the local heating of water molecules bound to the proteins and the other by the formation of reactive free radicals. To discriminate which is the likely or dominant mechanism we have studied the effects of thermal and UV denaturation of aqueous protein solutions with and without DHR-123 as fluorogenic probe using circular dichroism (CD), synchrotron radiation circular dichroism (SRCD), and fluorescence spectroscopies. The results indicated that the mechanism of protein denaturation induced by VUV and far-UV irradiation were mediated by the formation of reactive free radicals (FR) and reactive oxygen species (ROS). The development at Diamond B23 beamline for SRCD of a novel protein UV photo-stability assay based on consecutive repeated CD measurements in the far-UV (180–250 nm) region has been successfully used to assess and characterize the photo-stability of protein formulations and ligand binding interactions, in particular for ligand molecules devoid of significant UV absorption.     

Photo-oxidation in an O2 atmosphere: A powerful tool to elucidate the mechanism of UV-visible light oxidation of polymers - Application to the photodegradation of MDMO-PPV

This article describes a new approach to improve the analysis of the chemical modifications that result from the degradation of polymers under UV-visible light exposure in the presence of oxygen. The tool which is used consists of an irradiation chamber whose atmosphere is composed of ¹⁸O₂. The ¹⁸O₂ pressure inside the chamber and the hygrometry can be adjusted. In this study, particular attention was paid to the photo-oxidation of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV). Using infrared spectroscopy, irradiation under the oxygen 18 atmosphere allowed discrimination between compounds formed via fixation of oxygen from the atmosphere and those formed by reorganisation of the matrix. In addition, irradiation of MDMO-PPV in an ¹⁸O₂ wet atmosphere allowed for detection of the presence of phenyl formate and aromatic ketone functions. This permitted validating the mechanism of photo-oxidation previously proposed. Additionally, with regard to blends made with MDMO-PPV and methano-fullerene[6,6]-phenyl C₆₁-butyric acid methyl ester ([60] PCBM), it was demonstrated that this technique facilitates the identification of the photo-oxidation products formed.     

超声波辐射条件下锡(Ⅱ)催化合成二吲哚基甲烷的方法研究

研究了一种由Sn Cl2催化合成二吲哚基甲烷的高效方法。引用超声波辐射作为反应条件,在反应体系中加入当量的催化剂能够在短时间内合成出二吲哚基甲烷且分离方法简单易行。合成出的系列二吲哚基甲烷具有一定的光学性质,即在400~600 nm波长范围内范围内具有光吸收作用,且在受波长为370 nm光的激发下,会发出波长约为440 nm的紫光。     

Synthesis and properties of dithienylethene-based binuclear gold complexes and a palladium chlorine-bridged macrocycle

Two dithienylethene-based binuclear gold complexes and a palladium chlorine-bridged macrocycle bearing bis(phosphine) ligands have been synthesized. Their structures have been thoroughly characterized by NMR spectrometry, single-crystal X-ray diffraction, and elemental analyses. The two binuclear gold complexes display excellent photoisomerization properties upon irradiation with UV/Vis light in CH₂Cl₂. Moreover, we found that the introduction of metal atoms can stabilize the dithienylethene-based bis(phosphine) ligands, and that the absorption spectra of gold complexes 3 and 4 showed 6–12 nm red-shifts upon irradiation with UV light compared with those of the ligands 1 and 2. However, no such isomerization was observed when the palladium chlorine-bridged macrocycle 5 in CH₂Cl₂ was irradiated with UV light, but it showed excellent catalytic activity for the Suzuki coupling reaction. Moreover, we found that the non-photochromic macrocycle 5 can perform the photochromic reaction when the solution of CH₃CN was irradiated by UV light.     

光氧稳定剂对塑木复合材料性能的影响

以紫外光稳定剂531和抗氧剂2246为光氧稳定剂,研究了塑木复合材料受光氧影响时的弯曲性能、色泽变化、氧化诱导期和外观变化.研究表明,经紫外光照射后,光氧稳定剂对材料的弯曲性能影响不大,但添加有光氧稳定剂的材料的表面色泽变化小,发白不明显.在紫外光稳定剂531和抗氧剂2246的添加量分别为0.3%时,材料经300h紫外...     

Surface Modification of Multi-walled Carbon Nanotubes with Gaseous Oxygen and Chlorine Atoms

Multi-walled carbon nanotube (MWNT) paper was surface modified with gaseous oxygen and chlorine atoms, and analyzed by X-ray photoelectron spectroscopy (XPS). The oxygen atoms were produced by a low-pressure microwave (MW) plasma discharge of an Ar–O₂ mixture and the results were compared to a previous study using VUV photo-oxidation. Exposure to VUV photo-oxidation (λ= 104.8 and 106.7 nm) showed approximately the same level of oxidation (ca. 7.4 at% O) as the MW results (ca. 6.3 at% O) that were conducted in the absence of radiation from the plasma. Oxygen atoms reacted with the π-conjugation of the MWNTs to primarily produce the epoxide/ether groups. Chlorine atoms, which were generated by UV photolysis of Cl₂, reacted more readily than chlorine molecules with the nanotubes to yield saturation levels of ca. 13 at% Cl.     

Shielding Behavior of Gamma-Irradiated MoO<Subscript>3</Subscript> or WO<Subscript>3</Subscript>-Doped Lead Phosphate Glasses Assessed by Optical and FT Infrared Absorption Spectral Measurements

Undoped and MoO₃- or WO₃- doped lead phosphate glasses were prepared by the melting-annealing technique. The glasses were characterized through UV-visible and infrared measurements which were repeated after gamma irradiation. Optical spectrum of binary lead phosphate glass shows distinct ultraviolet bands correlated with unavoidable trace iron impurities within the chemicals used for the preparation of the glasses. UV-visible absorption spectra of MoO₃- or WO₃- doped glasses exhibit additional UV-visible bands which are related to the presence of four oxidation states of the two transition metal (molybdenum or tungsten) ions (Mo³⁺, Mo⁴⁺, Mo⁵⁺, Mo⁶⁺, W³⁺, W⁴⁺, W⁵⁺, W⁶⁺). The extra UV band is related to hexavalent (5d⁰) state while the rest of the visible bands are related to (350–440 nm - trivalent state), (450, 550, 650 nm - tetravalent state) while the broad band centered at about 770 nm (pentavalent state). The intensities of the absorption bands are observed to change with the transition metal content and their valencies. Infrared absorption spectra reveal distinct vibrational bands which are assigned to phosphate groups with sharing of Pb-O vibrations within both the range 460–620 cm^-1 and the range 900–1100 cm^-1 revealing a compact network structure. Gamma irradiation causes a minor increase in intensity of one of the UV band due to suggested photo-oxidation of some trace ferrous ions to additional ferric ions but the remaining spectral curve remains unaffected which is obviously related to some shielding effects of heavy atomic weight of PbO. This heavy metal oxide (PbO) is assumed to retard or prohibit the free passage of free electrons or positive holes generated during the irradiation process.     

Efficiency of 4,4′‐bis(N,N‐diethylamino) benzophenone for the polymerization of dimethacrylate resins in thick sections

The efficiency of 4,4′‐bis(N,N‐diethylamino)benzophenone (DEABP) for the polymerization of dimethacrylate monomers in thick sections ( 1 – 2 mm) was studied. DEABP (λ_max = 365 nm) represents a complete initiating system as it contains both ketone and amine functional groups. During irradiation, DEABP photobleaches at a fast rate causing deeper penetration of light through the underlying layers, but the photoinitiation efficiency (rate of polymerization per photon absorption rate) is relatively poor. As a result, irradiation of methacrylate monomers at 365 nm results in a slow average polymerization rate and a reduced monomer conversion for thick sections due to the light attenuation caused by the high absorptivity of DEABP and photolysis products. These results highlight the inherent interlinking of light attenuation and photobleaching rate in polymerization of thick sections. Copyright © 2011 Society of Chemical Industry     

Wavelength sensitivity of the photodegradation of poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) was photolyzed with monochromatic light of wavelengths 260, 280, 300, 320, 400, and 500 nm in vacuo by the use of the Okazaki Large Spectrograph. UV spectral changes, the quantum yields of main-chain scission (?cs), and effects of wavelength were investigated. UV spectral changes around 280 nm were observed with irradiation at 260 nm. The ?cs has a maximum value in case of irradiation with 300 nm light. It turned out that photodegradation of PMMA took place by irradiation of 260–320 nm light but did not by irradiation with the light longer wavelength than 340 nm. The average values of ?cs obtained in this work were 0.84 × 10^?4, 1.06 × 10^?4, 4.21 × 10^?4, 1.23 × 10^?4, 0, and 0 for irradiations at 260, 280, 300, 320, 400, and 500 nm, respectively. It was found that the photo-induced side-chain scission initiates the main-chain scission of PMMA by irradiation of 260 and 280 nm light. © 1993 John Wiley & Sons, Inc.     

Poly(vinyl alcohol) hollow microcapsules prepared by emulsification, salting out, and photo cross-linking method

Coumarin residues were conjugated to poly(vinyl alcohol) (PVA) by reacting epoxypropoxy coumarin (EPC) with the polymer. According to the peak areas on the ¹H NMR spectrum, EPC was calculated to be conjugated to every 283 repeating units (vinyl alcohols). A cyclic photo-dimerization and dedimerization of EPC of PVA-EPC conjugate were observed under a cyclic irradiation of 365 nm and 254 nm. The salting-out of the conjugate significantly took a place in the range of 0?C2.0M NaCl, and the phenomenon was observed at a lower concentration than that of unmodified PVA was. Oil-in-water emulsion was prepared as a template for the preparation of hollow microcapsules using chloroform as an oil phase and PVA-EPC as an emulsifier. The emulsion was stable for 24 hr in terms of droplet size. The wall surrounding droplets was built-up by the salting-out of PVA-EPC, and it was cross-linked by the irradiation of 365 nm. After chloroform was evaporated and salt was removed by a dialysis, hollow microcapsules were successfully obtained.     

Pattern of Peroxide Value Changes in Virgin Coconut Oil (VCO) Due to Photo-Oxidation Sensitized by Chlorophyll

The effect of chlorophyll in photo-oxidation of virgin coconut oil (VCO) during production and storage was studied. Photo-oxidation during VCO production was performed under accelerated conditions using fluorescent lights (4,000 lux) for 8 h. Peroxide values (PVs) and chlorophyll contents of the samples were measured at 1 h intervals. To compare the photo-oxidation during storage, VCO samples were separately stored under ambient and normal room light intensity (380–400 lux) for up to 4 months and PVs were measured weekly. The results indicated that relatively low light intensity during the settling stage of VCO production had no significant effect on photo-oxidation. Photo-oxidation of VCO, however, was observed during storage when exposed to high intensity fluorescent light. The degradation of chlorophyll content in VCO was evident during exposure to a high fluorescent light intensity which was accompanied by high lipid peroxide accumulation. A significant negative correlation between PV and chlorophyll content was found in VCO without light protection. The storage of VCO significantly increased the PV after 10 weeks. This study confirmed that chlorophyll which is naturally present in VCO even at a very low level (less than 0.1 ppm) could initiate a photo-oxidation reaction leading to quality deterioration during prolonged storage or display at retailers.     

The effectiveness of ultraviolet absorbers in PVC

The influence of some benzophenone-type ultraviolet absorbers in a general PVC formulation has been studied by determining rates of photo-oxidation when specimens were exposed to xenon-arc irradiation under controlled conditions. Replicates of the formulation but without the absorbers were similarly photo-oxidised behind a series of glass filters to provide a basis for assessing the effectiveness of the absorbers. Some changes in appearance of the specimens have also been measured and discussed in relation to the data on photo-oxidation rate.     

Synthesis and properties of dithienylethene-based binuclear gold complexes and a palladium chlorine-bridged macrocycle

Two dithienylethene-based binuclear gold complexes and a palladium chlorine-bridged macrocycle bearing bis(phosphine) ligands have been synthesized. Their structures have been thoroughly characterized by NMR spectrometry, single-crystal X-ray diffraction, and elemental analyses. The two binuclear gold complexes display excellent photoisomerization properties upon irradiation with UV/Vis light in CH₂Cl₂. Moreover, we found that the introduction of metal atoms can stabilize the dithienylethene-based bis(phosphine) ligands, and that the absorption spectra of gold complexes 3 and 4 showed 6-12 nm red-shifts upon irradiation with UV light compared with those of the ligands 1 and 2. However, no such isomerization was observed when the palladium chlorine-bridged macrocycle 5 in CH₂Cl₂ was irradiated with UV light, but it showed excellent catalytic activity for the Suzuki coupling reaction. Moreover, we found that the non-photochromic macrocycle 5 can perform the photochromic reaction when the solution of CH₃CN was irradiated by UV light.     

Fine Control of Nitrogen Content in N-doped Titania Photocatalysts Prepared from Layered Titania/Isostearate Nanocomposites for High Visible-Light Photocatalytic Activity

In this contribution, high photocatalytic activity under visible-light irradiation realized by means of the fine control of the nitrogen content in doped titania photocatalysts is reported. The photocatalyst samples were prepared from a layered titania/isostearate nanocomposite as precursor, and the fine control of nitrogen content was achieved by the adjustment of the amount of hybridized isostearate in the nanocomposite, preserving the crystallinity and specific surface area of the final samples. Photocatalytic activity under the UV-light irradiation (290 and 350 nm) decreases with nitrogen content. Under visible-light irradiation (470 nm), a maximum value of photocatalytic activity was observed at [N]/[Ti] = 0.0145, whereas the absorbance in the visible-light region increases with nitrogen content. Fine control of the doped-nitrogen content provides a possible route to achieving high visible-light photocatalytic activity where the maximum value of the apparent quantum yield under 470 nm light irradiation exceeds 2%.