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To study the effects of the position of the hexatrienyl moiety on the oxazole ring, novel substituted cis/trans-2/4/5-(2-vinylstyryl)oxazoles have been synthesized. These novel compounds were prepared by Wittig reaction from the diphosphonium salt of α,α'-o-xylenedibromide, formaldehyde and the corresponding 2-methyl-4-, 4-methyl-2-, 2-pheny-5- and 4-methyl-5-oxazolecarbaldehyde, respectively. Aldehydes were synthesized by using several synthetic approaches. By applying intramolecular photocycloaddition, 2-methyl-4-(2-vinylstyryl)-oxazole afforded, as major product, fused oxazoline-benzobicyclo[3.2.1]octene with small quantities of 4-(1,2-dihydronaphthalen-2-yl)-2-methyloxazole, as electrocyclization product. Upon irradiation of 4-methyl-5-(2-vinylstyryl)oxazole, endo- and exo-benzobicyclo[2.1.1]hexene products were formed by [2+2] cycloaddition; this was the first instance of the 1,4-closure to the bicyclo[2.1.1]hexene skeleton in the 2-, 4-, and 5-oxazole- stilbene derivatives studied so far. Derivatives 2-phenyl-5- and 4-methyl-2-(2-vinylstyryl)oxazole did not react and gave only high-weight molecular products but were crucial as a comparison in the overall mechanistic study. We have found that, depending on the position of the hexatrienyl moiety in the oxazole ring, as well as on the position of the methyl/phenyl substituents, these new vinylstyryl-2/4/5-oxazole derivatives show diverse photochemical behavior. [ABSTRACT FROM AUTHOR]

Numerous computational and spectroscopic studies have demonstrated the decisive role played by nonadiabatic coupling in photochemical reactions. Nonadiabatic coupling drives photochemistry when potential energy surfaces are nearly degenerate at avoided crossings or truly degenerate at unavoided crossings. The dynamics induced by nonadiabatic coupling are challenging to comprehend; here we describe a versatile one-dimensional model that is numerically tractable and illustrates fundamental aspects of nonadiabatic quantum dynamics. This model reinforces and builds on concepts taught in graduate-level quantum mechanics and therefore should be accessible to advanced undergraduate and graduate students. We use the model to demonstrate how the local topography of an unavoided crossing can affect a photochemical quantum yield. [ABSTRACT FROM AUTHOR]

The use of supramolecular interactions to control the reactivity of excited states is discussed with emphasis on covalent bond formation and catalysis. The latter is shown to apply both to the synthesis of organic compounds as well as to the preparation of inorganic materials. [ABSTRACT FROM AUTHOR]

A series of six Ru(arene) complexes, [(η6-p-cymene)Ru(dpb)(py-R)]2+ (1–6, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline, py-R = 4-substituted pyridine, R = N(CH3)2, NH2, OCH3, H, COOCH3 and NO2), were synthesized and their photochemical and photobiological properties were compared in detail. The electron push/pull character of the R groups has a significant impact on both ligand photodissociation and 1O2 generation of the complexes. The photoinduced DNA covalent binding capabilities increase from 1 to 6 under both aerobic and anaerobic conditions, and DNA photocleavage occurs simultaneously in aerobic environments. 4 has the most potent phototoxicity against human lung carcinoma A549 cells among the examined complexes. The substituent effect may be ascribed to the influences of the R groups on the energy levels of 3MC and 3MLCT states as well as the energy gaps between 3MC, 3MLCT and dpb-based 3IL states. Similar chemical modification on bidentate and arene ligands or other sites of the pyridine ligand may lead to more efficient agents with PDT and/or PACT activities. [ABSTRACT FROM AUTHOR]

One of the most habitable environments in the Solar System outside of Earth may exist underneath the ice on Europa. In the near future, our best chance to look for chemical signatures of a habitable environment (or life itself) will likely be at the inhospitable icy surface. Therefore, it is important to understand the ability of organic signatures of life and life itself to persist under simulated europan surface conditions. Toward that end, this work examined the UV photolysis of Bacillus subtilis spores and their chemical marker dipicolinic acid (DPA) at temperatures and pressures relevant to Europa. In addition, inactivation curves for the spores at 100 K, 100 K covered in one micron of ice, and 298 K were measured to determine the probability for spore survival at the surface. Fourier transform infrared spectra of irradiated DPA showed a loss of carboxyl groups to CO2 as expected but unexpectedly showed significant opening of the heterocyclic ring, even for wavelengths >200 nm. Both DPA and B. subtilis spores showed identical unknown spectral bands of photoproducts after irradiation, further highlighting the importance of DPA in the photochemistry of spores. Spore survival was enhanced at 100 K by ∼5× relative to 298 K, but 99.9% of spores were still inactivated after the equivalent of ∼25 h of exposure on the europan surface. Key Words: Bacillus subtilis-DPA-Viability-Icy worlds-Europa. Astrobiology 15, 20-31. [ABSTRACT FROM AUTHOR]

A carbon nitride/ TiO2 nanofiber heterojunction photocatalyst that is responsive to simulated solar light is prepared by a simple self-assembly method. X-ray diffraction ( XRD), UV-vis spectroscopy, scanning electron microscopy ( SEM), electrochemical impedance spectroscopy ( EIS), and X-ray photoelectron spectroscopy ( XPS) are used to characterize the prepared catalysts. The results indicate that the TiO2 nanofiber is coated by the g- C3N4 sheet to form a core/shell structure, which is favorable for the fast interfacial charge transfer and separation of the photogenerated electron-hole pairs. The activity and stability of carbon nitride/ TiO2 nanofiber heterojunction photocatalyst are tested in the photocatalytic degradation of rhodamine B ( RhB) under simulated solar light. The rate constant of TiNF(0.3)- CN is found to be 0.044 min−1, which is 4 and 2.2 times higher than that of single TiO2 nanofiber and g- C3N4 , respectively. A possible mechanism is proposed. [ABSTRACT FROM AUTHOR]

Glutathione-capped metal nanoclusters (Aux-GSH NCs) which exhibit molecular-like properties are employed as a photosensitizer for hydrogen generation in a photoelectrochemical cell (PEC) and a photocatalytic slurry reactor. The reversible reduction (E° = -0.63 V vs RHE) and oxidation (E° = 0.97 and 1.51 V vs RHE) potentials of these metal nanoclusters make them suitable for driving the water-splitting reaction. When a mesoscopic Ti02 film sensitized by Aux-GSH NCs is used as the photoanode with a Pt counter electrode in aqueous buffer solution (pH = 7), we observe significant photocurrent activity under visible light (400-500 nm) excitation. Additionally, sensitizing Pt/Ti02 nanoparticles with Aux-GSH NCs in an aqueous slurry system and irradiating with visible light produce H2 at a rate of 0.3 mmol of hydrogen/h/g of Aux-GSH NCs. The rate of H2 evolution is significantly enhanced (∼5 times) when a sacrificial donor, such as EDTA, is introduced into the system. Using metal nanoclusters as a photosensitizer for hydrogen generation lays the foundation for the future exploration of other metal nanoclusters with well-controlled numbers of metal atoms and capping ligands. [ABSTRACT FROM AUTHOR]

We report a new strategy for the photomediated phase transfer of luminescent quantum dots, QDs, and potentially other inorganic nanocrystals, from hydrophobic to polar and hydrophilic media. In particular, we demonstrate that UV-irradiation (? < 400 nm) promotes the in situ ligand exchange on hydrophobic CdSe QDs with lipoic acid (LA)-based ligands and their facile QD transfer to polar solvents and to buffer media. This convenient method obviates the need to use highly reactive agents for chemical reduction of the dithiolane groups on the ligands. It maintains the optical and spectroscopic properties of the QDs, while providing high photoluminescence yield and robust colloidal stability in various biologically relevant conditions. Furthermore, development of this technique significantly simplifies the preparation and purification of QDs with sensitive functionalities. Application of these QDs to imaging the brain of live mice provides detailed information about the brain vasculature over the period of a few hours. This straightforward approach offers exciting possibilities for expanded functional compatibilities and reaction orthogonality on the surface of inorganic nanocrystals. [ABSTRACT FROM AUTHOR]

The photochemical conversion of selected hydroxylated polybrominated diphenyl ethers (OH-PBDEs) to dioxins and other products was investigated. OH-PBDEs, which are both transformation products of polybrominated diphenyl ethers and naturally occurring compounds, undergo direct photolysis to yield a number of products that may have a higher toxicity than their parent. The compounds investigated were 6-OH-PBDE 99, 6′-OH-PBDE 100, and 6′-OH-PBDE 118. Of special interest was 6′-OH-PBDE 118, a potential transformation product of PBDE 153 that is capable of photochemically generating 2,3,7,8-tetrabromodibenzo-p-dioxin, the most toxic brominated dioxin congener. Photolysis experiments were conducted at two different pH values to assess the photochemical behavior of both the phenol and phenolate form of the compounds. The percent conversion to dioxin and other photoproducts was determined and the natural product, 6-OH-PBDE 99, was found to have the highest conversion to dioxin (7%). The reaction quantum yields ranged from 0.027 to 0.16 across all photolysis conditions. In addition, it is shown that all three compounds are capable of photochemically generating other compounds of concern, including brominated phenols and a dibenzofuran. [ABSTRACT FROM AUTHOR]

It is shown here that carbamazepine (CBZ) would undergo direct photolysis and reaction with •OH as the main phototransformation pathways in surface waters. Environmental lifetimes are expected to vary from a few weeks to several months, and predictions are in good agreement with available field data. Acridine (I) and 10,11-dihydro-10,11-trans-dihydroxy-CBZ (V) are the main quantified phototransformation intermediates upon direct photolysis and •OH reaction, respectively. The photochemical yield of mutagenic I from CBZ is in the 3-3.5% range, and it is similar for both direct photolysis and •OH reaction: it would undergo limited variation with environmental conditions. In contrast, the yield of V would vary in the 4-8.5% range depending on the conditions, because V is formed from CBZ by •OH (9.0% yield) more effectively than upon direct photolysis (1.4% yield). Other important photointermediates, mostly formed from CBZ upon •OH reaction, are an aromatic-ring-dihydroxylated CBZ (VI) and N,N-bis(2-carboxyphenyl)urea (VII). Compounds VI and VII are formed by photochemistry and are not reported as human metabolites; thus, they could be used as tracers of CBZ phototransformation in surface waters. Interestingly, VI has recently been detected in river water. [ABSTRACT FROM AUTHOR]

The use of integrated assessment models, in air quality policy, which combines atmospheric models with others from different fields, raises the need of developing specific air quality modelling concepts. The air quality model, AUSTAL2000-AYLTP uses an adapted version of AUSTAL2000 model to calculate transport coupled with a fast photochemical module. Two approaches are compared: one using a look-up table and the other using a coupled box model. The lookup table has been built using the OZIPR model by simulating a large set of possible combinations of meteorological variables and precursor concentrations. The second approach consists of coupling the Lagrangian model AUSTAL2000 with the OZIPR box model. In both approaches the photochemistry is included in the mode by using a quasi-linear reaction rates coefficient which is used to affect the mass of the Lagrangian particles. We discuss the differences and the suitability of the two model versions, through exploring CPU time flexibility, applicability and accuracy. [ABSTRACT FROM AUTHOR]

The photolysis of o-tolualdehyde by natural sunlight has been investigated at the large outdoor European Photoreactor (EUPHORE) in Valencia, Spain. The photolysis rate coefficient was measured directly under different solar flux levels, with values in the range j(o-tolualdehyde) = (1.62-2.15) × 10-4 s-1 observed, yielding an average value of j(o-tolualdehyde)/j(NO2) = (2.53 ± 0.25) × 10-2. The estimated photolysis lifetime is 1-2 h, confirming that direct photolysis by sunlight is the major atmospheric degradation pathway for o-tolualdehyde. Published UV absorption cross-section data were used to derive an effective quantum yield (290-400 nm) close to unity, within experimental error. Possible reaction pathways for the formation of the major photolysis products, benzocyclobutenol (tentatively identified) and o-phthalaldehyde, are proposed. Appreciable yields (5-13%) of secondary organic aerosol (SOA) were observed at EUPHORE and also during supplementary experiments performed in an indoor chamber using an artificial light source. Off-line analysis by gas chromatography-mass spectrometry allowed identification of o-phthalaldehyde, phthalide, phthalic anhydride, o-toluic acid, and phthalaldehydic acid in the particle phase. [ABSTRACT FROM AUTHOR]

Review: 141 refs. [ABSTRACT FROM AUTHOR]