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S Gebauer, J L Grenfell, J W Stock, R Lehmann, M Godolt, P von Paris, H Rauer
Understanding the evolution of Earth and potentially habitable Earth-like worlds is essential to fathom our origin in the Universe. The search for Earth-like planets in the habitable zone and investigation of their atmospheres with climate and photochemical models is a central focus in exoplanetary science. Taking the evolution of Earth as a reference for Earth-like planets, a central scientific goal is to understand what the interactions were between atmosphere, geology, and biology on early Earth. The Great Oxidation Event in Earth's history was certainly caused by their interplay, but the origin and controlling processes of this occurrence are not well understood, the study of which will require interdisciplinary, coupled models...
January 2017: Astrobiology
Francesco Barsotti, Giovanni Ghigo, Silvia Berto, Davide Vione
The photophysics and photochemistry of 4-hydroxybenzophenone (4HOBP) are interesting because they can give some insight into the behavior of humic material. Here we show that 4HOBP has a number of fluorescence peaks: (i) an intense one at excitation/emission wavelengths Ex/Em ∼ 200-230/280-370 nm, likely due to an excitation transition from S0 to S5 or S6, followed by S2 → S0 in emission (Sn denotes the singlet states of 4HOBP); (ii) a minor peak at Ex/Em ∼ 270-300/320-360 nm (S0 → S2 in absorption and S2 → S0 in emission), and (iii) very interesting signals in the typical emission region of humic substances, most notably at Ex/Em ∼ 200-220/400-500 nm and Ex/Em ∼ 260-280/400-470 nm (in both cases the emission corresponded to an S1 → S0 transition)...
January 19, 2017: Photochemical & Photobiological Sciences
Dian E Romonosky, Ying Li, Manabu Shiraiwa, Alexander Laskin, Julia Laskin, Sergey A Nizkorodov
Formation of secondary organic aerosols (SOA) from biogenic volatile organic compounds (BVOC) occurs via O3- and OH-initiated reactions during the day and reactions with NO3 during the night. We explored the effect of these three oxidation conditions on the molecular composition and aqueous photochemistry of model SOA prepared from two common BVOC. A common monoterpene, α-pinene, and sesquiterpene, α-humulene, were used to form SOA in a smog chamber via BVOC + O3, BVOC + NO3, and BVOC + OH + NOx oxidation...
January 18, 2017: Journal of Physical Chemistry. A
José Ignacio García-Plazaola, Beatriz Fernández-Marín, Juan Pedro Ferrio, Josu G Alday, Günter Hoch, Damien Landais, Alexandru Milcu, David T Tissue, Jordi Voltas, Arthur Gessler, Jacques Roy, Víctor Resco de Dios
There is increasing evidence that the circadian clock is a significant driver of photosynthesis that becomes apparent when environmental cues are experimentally held constant. We studied whether the composition of photosynthetic pigments is under circadian regulation, and whether pigment oscillations lead to rhythmic changes in photochemical efficiency. To address these questions, canopies of bean and cotton were maintained, after an entrainment phase, under constant (light or darkness) conditions for 30-48 h...
January 18, 2017: Plant, Cell & Environment
Martin Herder, Fabian Eisenreich, Aurelio Bonasera, Anna Grafl, Lutz Grubert, Michael Pätzel, Jutta Schwarz, Stefan Hecht
Among bistable photochromic molecules diarylethenes (DAEs) possess the distinct feature that upon photoisomerization they undergo a large modulation of their π-electronic system, accompanied by a marked shift of the HOMO/LUMO energies and hence oxidation/reduction potentials. In order to exploit such photoswitchable systems it is important to precisely adjust the absolute position of their HOMO and LUMO levels and to maximize the extent of the photoinduced shifts of these energy levels. Here, we present a comprehensive study detailing how variation of the substitution pattern of DAE compounds, in particular using strongly electron-accepting and chemically stable trifluoromethyl groups either in the periphery or at the reactive carbon atoms, allows for the precise tuning of frontier molecular orbital levels over a broad energy range and the generation of photoinduced shifts of more than 1 eV...
January 17, 2017: Chemistry: a European Journal
Madhulika Singh, Bishwajit Kumar Kushwaha, Samiksha Singh, Vipin Kumar, Vijay Pratap Singh, Sheo Mohan Prasad
The present study investigates modulation in hexavalent chromium [Cr(VI) 25 μM] toxicity by sulphur (S; 0.5, 1.0 and 1.5 mM S as low (LS), medium (MS) and high sulphur (HS), respectively) in Solanum melongena (eggplant) seedlings. Biomass accumulation (fresh and dry weights), photosynthetic pigments, photosynthetic oxygen evolution and S content were declined by Cr(VI) toxicity. Furthermore, fluorescence characteristics (JIP-test) were also affected by Cr(VI), but Cr(VI) toxicity on photosystem II photochemistry was ameliorated by HS treatment via reducing damaging effect on PS II reaction centre and its reduction side...
December 27, 2016: Plant Physiology and Biochemistry: PPB
Neil C Cole-Filipiak, Michael Staniforth, Natércia D N Rodrigues, Yoann Peperstraete, Vasilios G Stavros
To explore the effects of ring substitution on dissociation dynamics, the primary photochemistry of 2-ethylpyrrole has been explored using ultrafast ion imaging techniques. Photoexcitation to the S1 state, a πσ* state, in the range of 238 to 265 nm results in cleavage of the N-H bond with an H-atom appearance lifetime of ca. 70 fs. The insensitivity of this lifetime to photon energy, combined with a small kinetic isotope effect, suggests that tunneling does not play a major role in N-H bond cleavage. Total kinetic energy release spectra reveal modest vibrational excitation in the radical counter-fragment, increasing with photon energy...
January 10, 2017: Journal of Physical Chemistry. A
Yong H Kim, Hyun Soo Kim, Chul H Song
A reactive plume model (RPM) was developed to comprehensively consider power-plant plume photochemistry with 255 condensed photochemical reactions. The RPM can simulate two main components of power-plant plumes: turbulent dispersion of plumes and compositional changes of plumes via photochemical reactions. In order to evaluate the performance of the RPM developed in the present study, two sets of observational data obtained from the TexAQS II 2006 (Texas Air Quality Study II 2006) campaign were compared with RPM-simulated data...
January 9, 2017: Environmental Science & Technology
K Hölz, J Lietard, M M Somoza
Ultraviolet light emitting diodes (UV LEDs) have become widespread in chemical research as highly efficient light sources for photochemistry and photopolymerization. However, in more complex experimental setups requiring highly concentrated light and highly spatially resolved patterning of the light, high-pressure mercury arc lamps are still widely used because they emit intense UV light from a compact arc volume that can be efficiently coupled into optical systems. Advances in the deposition and p-type doping of gallium nitride have recently permitted the manufacture of UV LEDs capable of replacing mercury arc lamps also in these applications...
January 3, 2017: ACS Sustainable Chemistry & Engineering
Maximilian Krämer, Uwe H F Bunz, Andreas Dreuw
Diphenylacetylene (tolane) exhibits a rich photochemistry which depends on the relative orientation of the phenyl rings and the external conditions. Here state-of-the-art quantum chemical methods based on the algebraic diagrammatic construction scheme for the polarization propagator of second order are employed to investigate the luminescence properties of tolane and its derivatives. It is explained why different derivatives of tolane exhibit different absorbtion but practically identical fluorescence spectra, why the fluorescence quantum yield and the population of a "dark" state is temperature dependent and why initially twisted tolanophanes phosphoresce in glassy media at 77K while planar ones do not...
January 6, 2017: Journal of Physical Chemistry. A
Yuanying Li, Fengyi Liu, Bin Wang, Qingqing Su, Wenliang Wang, Keiji Morokuma
We report the light-driven isomerization mechanism of a fluorene-based light-driven rotary motor (corresponding to Feringa's 2nd generation rotary motor, [M. M. Pollard et al., Org. Biomol. Chem. 6, 507-512 (2008)]) at the complete active space self-consistent field (CASSCF) and spin-flip time-dependent density functional theory (TDDFT) (SFDFT) levels, combined with the complete active space second-order perturbation theory (CASPT2) single-point energy corrections. The good consistence between the SFDFT and CASSCF results confirms the capability of SFDFT in investigating the photoisomerization step of the light-driven molecular rotary motor, and proposes the CASPT2//SFDFT as a promising and effective approach in exploring photochemical processes...
December 28, 2016: Journal of Chemical Physics
Wen-Jie Wu, Quan-Song Li, Ze-Sheng Li
Understanding the photochemistry of organoboron compounds is essential to expand optoelectronic applications. In this work, the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combining with density functional theory (DFT) have been employed to investigate the elimination mechanisms of compound 6,7-dihydro-5(4)-benzo[d]pyrido[2,1-f][1,2]azaborininr (B4) on the ground state (S0) and the first excited state (S1). B4 is one of the 1,2-B,N-heterocycles that undergo competitive thermal elimination and photoelimination depending on the substitution groups on the B atom and the chelate backbone, thus providing a high-selectivity synthesis strategy for luminescent compounds...
January 18, 2017: Journal of Physical Chemistry. A
Jennifer A Reeves, Michael L Allegrezza, Dominik Konkolewicz
Vinyl ketone polymers, including phenyl vinyl ketone (PVK), are an important class of polymers due to their ability to degrade upon irradiation with ultraviolet light which makes them useful for a variety of applications. However, traditional radical methods for synthesizing PVK polymers give rise to poor control or are unable to produce block copolymers. This work uses reversible addition-fragmentation chain transfer polymerization (RAFT) and photochemistry to polymerize PVK. When visible blue radiation of 440 ± 10 nm is used as the light source for the photopolymerization, rapid polymerization and well-defined polymers are created...
January 3, 2017: Macromolecular Rapid Communications
Shuyang Zhen, Marc W van Iersel
The efficiency of monochromatic light to drive photosynthesis drops rapidly at wavelengths longer than 685nm. The photosynthetic efficiency of these longer wavelengths can be improved by adding shorter wavelength light, a phenomenon known as the Emerson enhancement effect. The reverse effect, the enhancement of photosynthesis under shorter wavelength light by longer wavelengths, however, has not been well studied and is often thought to be insignificant. We quantified the effect of adding far-red light (peak at 735nm) to red/blue or warm-white light on the photosynthetic efficiency of lettuce (Lactuca sativa)...
December 15, 2016: Journal of Plant Physiology
Nursel Acar, Cenk Selçuki, Emine Coşkun
Schiff bases have many chemical and biological applications in medicine and pharmaceuticals due to the presence of an imine group (-C=N-). These bases are used in many different fields of technology, and in photochemistry because of their photochromic properties. Here, the structural and electronic properties of the Schiff base formed by tacrine and saccharin (TacSac) were explored using density functional theory with the B3LYP, M06-2X, M06L, and ωB97XD functionals in combination with the 6-311++G(d,p) basis set...
January 2017: Journal of Molecular Modeling
Yafang Cheng, Guangjie Zheng, Chao Wei, Qing Mu, Bo Zheng, Zhibin Wang, Meng Gao, Qiang Zhang, Kebin He, Gregory Carmichael, Ulrich Pöschl, Hang Su
Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. Sulfate is a major component of fine haze particles. Record sulfate concentrations of up to ~300 μg m(-3) were observed during the January 2013 winter haze event in Beijing. State-of-the-art air quality models that rely on sulfate production mechanisms requiring photochemical oxidants cannot predict these high levels because of the weak photochemistry activity during haze events...
December 2016: Science Advances
Yanping Tang, Xin Sun, Tao Wen, Mingjie Liu, Mingyan Yang, Xuefei Chen
The aim of this study is to investigate whether exogenous application of salicylic acid (SA) could modulate the photosynthetic capacity of soybean seedlings in water stress tolerance, and to clarify the potential functions of terminal oxidase (plastid terminal oxidase (PTOX) and alternative oxidase (AOX)) in SA' s regulation on photosynthesis. The effects of SA and water stress on gas exchange, pigment contents, chlorophyll fluorescence, enzymes (guaiacol peroxidase (POD; EC, superoxide dismutase (SOD; EC 1...
November 25, 2016: Plant Physiology and Biochemistry: PPB
Chun Guan, Xinling Li, Wugao Zhang, Zhen Huang
Author: The present work, involving the formation of NO and nitrous acid (HONO) and the nitration of polycyclic aromatic hydrocarbon (PAHs) to nitro-PAHs as well as the uptake coefficients of NO2, has been performed on a normal-pressure flow reactor to identify the nitration products during the heterogeneous reaction of soot toward NO2 in the dark and under simulated sunlight. Two types of soot particles, namely the commercial black carbon (BC) and the diesel engine soot (ES), were selected as the studied soot to compare the impacts of soot properties on heterogeneous nitration...
January 19, 2017: Journal of Physical Chemistry. A
Dario Cambié, Fang Zhao, Volker Hessel, Michael G Debije, Timothy Noël
The use of solar light to promote chemical reactions holds significant potential with regard to sustainable energy solutions. While the number of visible light-induced transformations has increased significantly, the use of abundant solar light has been extremely limited. We report a leaf-inspired photomicroreactor that constitutes a merger between luminescent solar concentrators (LSCs) and flow photochemistry to enable green and efficient reactions powered by solar irradiation. This device based on fluorescent dye-doped polydimethylsiloxane collects sunlight, focuses the energy to a narrow wavelength region, and then transports that energy to embedded microchannels where the flowing reactants are converted...
December 22, 2016: Angewandte Chemie
Guannan Chen, Mingli Ni, Haiyan Peng, Feihong Huang, Yonggui Liao, Mingkui Wang, Jintao Zhu, V A L Roy, Xiaolin Xie
Holographic photopolymer composites have garnered a great deal of interest in recent decades, not only because of their advantageous light sensitivity but also due to their attractive capabilities of realizing high capacity three-dimensional (3D) data storage that is long-term stable within two-dimensional (2D) thin films. For achieving high performance holographic photopolymer composites, it is of critical importance to implement precisely spatiotemporal control over the photopolymerization kinetics and gelation during holographic recording...
January 18, 2017: ACS Applied Materials & Interfaces
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