Was Licht bewirken kann

Light is based on photons. Therefore, in Part 1 the current state of knowledge on photons was treated. Then this part concentrates on the importance of the sun as a natural source of radiation and various artificial radiation sources. In the focus of Part 2 are important examples of the interaction of photons with matter. The solar irradiation with photosynthesis, which is discussed briefly, is the starting point of the Earth's biosphere. Photons as the smallest tools are incorporated with their energy into chemical processes of photocatalysis and photochemistry. Solar irradiation is also a prerequisite for physical energy in solar cells and also thermal solar heat. Photons from solar radiation and also artificial radiation sources will play an increasing role in a photon economy.     

Photochemical conversion and storage of solar energy

The possibilities for the photochemical storage of solar energy are examined from the standpoint of maximum efficiency and mechanism. Loss factors are considered for a general endergonic photochemical reaction and it is concluded that a realistic maximum solar energy storage efficiency for any photochemical system is 15–16%. The natural process of photochemical solar energy storage, namely, photosynthesis, is analyzed and it is found that the maximum solar energy storage efficiency of photosynthesis is 9.5 ± 0.8%. Kinetic and thermodynamic limitations on a photochemical energy storage process are identified and it is shown that the desirable production of hydrogen and oxygen from water probably cannot be sensitized with visible light if only one photochemical step is employed. However, by analogy with the mechanism of photosynthesis, two photochemical reactions operating in series permit a full utilization of the photochemically active part of the solar spectrum. A possible scheme is described and analyzed as to its possibilities and potential difficulties. Finally, some practical considerations are presented not only for the photochemical production of hydrogen but also for solid state photovoltaic devices.     

Surface-enhanced Raman spectroscopy toward application in plasmonic photocatalysis on metal nanostructures

Among photothermal, photovoltaic and photochemical techniques, photochemistry is superior in energy storage and transportation by converting photons into chemical fuels. Recently plasmonic photocatalysis, based on localized surface plasmon resonance (LSPR) generated from noble metal nanostructures, has attracted much attention. It promotes photochemical reaction efficiency by optimizing the solar spectrum absorption and the surface reaction kinetics. The deeper understanding is in urgent need for the development of novel plasmonic photocatalysts. Surface-enhanced Raman spectroscopy (SERS), which is also originated from the LSPR effect, provides an excellent opportunity to probe and monitor plasmonic photoreactions in situ and in real-time, with a very high surface sensitivity and energy resolution. Here, fundamentals of plasmonic photocatalysis and SERS are first presented based on their connections to the LSPR effect. Following by a validity analysis, latest studies of SERS applied for the plasmon mediated photochemical reaction are reviewed, focusing on the reaction kinetics and mechanism exploration. Finally, limitations of the present study, as well as the future research directions, are briefly analyzed and discussed.     

Spatiotemporal Utilization of Latent Heat in Erythritol-based Phase Change Materials as Solar Thermal Fuels

Solar thermal fuels (STFs) have been particularly concerned as sustainable future energy due to their impressive ability to store solar energy in chemical bonds and controllably release thermal energy. However, currently studied STFs mainly focus on molecule-based materials with high photochemical activity, toxicity, and compromised features, which greatly restricts their applications in practical scenarios of solar energy utilization. Herein, we present a novel erythritol-based composite phase change material (PCM) as a new type of STFs with an outstanding capability to store solar energy as latent heat in its stable supercooling state and release thermal energy as needed. This composite PCM with stored thermal energy can be maintained stably at room temperature and subsequently release latent heat as high as 224.9 J/g during the crystallization process triggered by thermal stimuli. Remarkably, solar energy can be converted into latent heat stored in the composite PCM over months. Through mechanical stimulations, the released latent heat can increase the temperature of the composite up to 91 °C. This work presents a new concept of using spatiotemporal storage and release of latent heat in PCMs for solar energy utilization, making it a potential candidate as STFs for developing future clean energy techniques.     

ULTRAVIOLET ACTION SPECTRA (280 to 380 nm) AND SOLAR EFFECTIVENESS SPECTRA FOR HIGHER PLANTS

Several ultraviolet (UV) action spectra that typify the responses of higher plants to irradiation by wavelengths between 280 nm and 380 nm are shown. An attempt is made to generate common spectra that may be used, at least temporarily, to represent the effects of UV on such important biological parameters as photosynthesis. The goal is to provide an estimate of plant response to solar UV and to the potential increase in ground level UV postulated for a depleted stratospheric ozone layer. Solar plant damage effectiveness curves are generated under "normal" solar UV conditions, and under an assumed UV increase corresponding to a 16% depletion in total ozone. Additional effects due to ozone depletion are concentrated in the UV-B region, especially at wavelengths between about 297 nm and 315 nm. Common features of these effectiveness curves are noted, and limitations are pointed out. As expected, no common spectrum has been found that can substitute for any specific spectrum nor that is unique enough to provide more than a limited first approximation of a plant damage spectrum. Additional information must be generated to fulfill this need.     

Assessment of the UVR protection provided by different tree species

In recent years, SunSmart campaigns have emphasized the importance of the use of shade as a strategy in the reduction of human exposure to solar UV radiation (UVR), particularly in early life with the provision of shade in schools. Trees can play an important role in shade provision, either as the main shade provider or to augment shade structures and increase UVR protection provided to the general population. A study to measure the protection provided by a range of trees common in Australian urban environments was undertaken during the summers of 2004/2005 and 2005/2006. Solar UVR beneath the trees was measured using UVR sensitive polysulphone badges positioned horizontally within the shaded area and were compared with those in full sunshine to give an indication of the protection provided. Measurements made on sunny days during the months of October to April indicated that the shade cover provided by the trees depended upon the tree species and changed with season as a result of changing foliage and sun angles. Measured protection factors ranged from 5 to 10 and were generally a maximum in the height of summer when the sun was highest in the sky and the foliage was densest.     

Ultraviolet photochemistry of ethane: implications for the atmospheric chemistry of the gas giants

Chemical processing in the stratospheres of the gas giants is driven by incident vacuum ultraviolet (VUV) light. Ethane is an important constituent in the atmospheres of the gas giants in our solar system. The present work describes translational spectroscopy studies of the VUV photochemistry of ethane using tuneable radiation in the wavelength range 112 ≤ λ ≤ 126 nm from a free electron laser and event-triggered, fast-framing, multi-mass imaging detection methods. Contributions from at least five primary photofragmentation pathways yielding CH₂, CH₃ and/or H atom products are demonstrated and interpreted in terms of unimolecular decay following rapid non-adiabatic coupling to the ground state potential energy surface. These data serve to highlight parallels with methane photochemistry and limitations in contemporary models of the photoinduced stratospheric chemistry of the gas giants. The work identifies additional photochemical reactions that require incorporation into next generation extraterrestrial atmospheric chemistry models which should help rationalise hitherto unexplained aspects of the atmospheric ethane/acetylene ratios revealed by the Cassini–Huygens fly-by of Jupiter.

The vacuum ultraviolet photodissociation dynamics of ethane provide clues for modelling the atmospheric chemistry of the gas giants.     

Ionic Pathways in the Photochemistry of Cyclic Sulfite Esters

The photochemistry of cyclic carbonate esters proceeds by the photochemical extrusion of carbon dioxide to give 1, 3‐diradicals which produce oxiranes as well as other radical derived species. The corresponding cyclic sulfite esters, upon irradiation, give intermediates that are trapped by alcohols yet generate no oxiranes. These results are consistent with ionic intermediates.     

Laser photochemistry of organometallic compounds related to applications in microelectronics

Photochemistry of organometallic compounds achieves a marriage of a rich variety of organometallic chemistry and the full potential of electronically excited states of molecules. The application of lasers as light sources adds a great many new features to these studies, which cannot be attained by other means, because lasers provide light of such a high quality, e.g. a high-intensity, energetic (i.e. wavelength) purity, a high degree of coherence, and a high spatial and temporal resolution. Laser photochemistry of organometallic compounds, such as laser photochemical vapor deposition (LPCVD), laser ablation, and photochemical dry etching, forms the basis of many important industrial processes which sustain the present-day microelectronics industries. Lasers are used not only to photodissociate organometallic molecules, but to monitor the reaction steps by probing the starting material, chemical intermediate, or final product by many laser-based spectroscopic methods. Although it is a very young area of science (the first laser was operated in 1960), this research area is now really ebullient, as a result of strong interest from both the fundamental and the practical sides. Laser photochemistry of organometallic compounds extends a wide and fertile research frontier, full of challenge and novel possibilities. In the present review, the present status of laser (ultraviolet and visible) photochemistry of organometallic compounds related to these industrial applications is briefly reviewed, with special emphasis on the basic studies of the relevant photochemistry and their relationship to photochemical processes on solid surfaces.     

Energy‐Efficient Solar Photochemistry with Luminescent Solar Concentrator Based Photomicroreactors

The sun is the most sustainable light source available on our planet, therefore the direct use of sunlight for photochemistry is extremely appealing. Demonstrated here, for the first time, is that a diverse set of photon‐driven transformations can be efficiently powered by solar irradiation with the use of solvent‐resistant and cheap luminescent solar concentrator based photomicroreactors. Blue, green, and red reactors can accommodate both homogeneous and multiphase reaction conditions, including photochemical oxidations, photocatalytic trifluoromethylation chemistry, and metallaphotoredox transformations, thus spanning applications over the entire visible‐light spectrum. To further illustrate the efficacy of these novel solar reactors, medicinally relevant molecules, such as ascaridole and an intermediate of artemisinin, were prepared as well.     

Photochemistry with microwaves: Catalysts and environmental applications

Microwave radiation has recently become an active source of thermal energy in numerous chemical reactions. As such, the microwave energy is not ordinarily and is not likely to be used to drive photochemical reactions. Accordingly, is the role of microwaves then relegated solely to be a source of heat? They do not have to be since photochemical reactions can be activated indirectly by microwaves using the UV light emitted from certain gas-fills excited by microwave radiation. This article examines the microwave radiation not only as a dielectric heat source but also a source of vacuum-UV radiation and UV light through microwave discharge electrodeless lamp devices, which in some cases (depending on design) can also serve as photoreactors.     

Flow Photochemistry as a Tool in Organic Synthesis

Photochemical transformations of molecular building blocks have become an important and widely recognized research field in the past decade. Detailed and deep understanding of novel photochemical catalysts and reaction concepts with visible light as the energy source has enabled a broad application portfolio for synthetic organic chemistry. In parallel, continuous-flow chemistry and microreaction technology have become the basis for thinking and doing chemistry in a novel fashion with clear focus on improved process control for higher conversion and selectivity. As can be seen by the large number of scientific publications on flow photochemistry in the recent past, both research topics have found each other as exceptionally well-suited counterparts with high synergy by combining chemistry and technology. This review will give an overview on selected reaction classes, which represent important photochemical transformations in synthetic organic chemistry, and which benefit from mild and defined process conditions by the transfer from batch to continuous-flow mode.     

Solar purification and potabilization of water containing dyes

Organic pollutant removal is the main field of water photocatalytic decontamination. Molecules such as pesticides (herbicides, insecticides, fungicides, etc.) or dyes are totally destroyed and mineralized into CO₂ and innocuous inorganic anions (Cl^?, SO ₄ ^2? , NO ₃ ^? ). Presently, two azo-dyes (i.e., containing the-N=N-azo group), Cibacron Brilliant Red 3B-A and Remazol Black B (Reactive Black 5), were successfully destroyed and totally mineralized. The stoichiometric coefficients of the total degradation, as well as the mass balances have been established with different analytical tools: TOC for carbon, DCO for oxygen, ionic-HPLC for heteroatoms (N, S, P) and pH-metry for hydrogen. Moreover, nitrogen balance has been established during the photocatalytic degradation of the dyes by considering not only nitrate and ammonium ions in the solution, but also the formation of N₂ in the gas phase. The quantification of N₂ molecules suggests that the photocatalytic degradation of azo-compounds is 100% selective in generating gaseous dinitrogen. The reaction mechanism was first determined in a laboratory photoreactor, before degradation in larger pilot solar photoreactors, using UV-A radiant flux from the sun in a new sub-discipline called heliophotocatalysis.     

Industrial Applications of Photochemical Syntheses

The principal industrial applications of photochemistry have so far been in the fields of free-radical chlorination, sulfochlorination, sulfoxidation, and nitrosation. In addition, however, photochemical reactions are being utilized on an increasing scale for the synthesis of vitamins, drugs, and fragrances. The present article surveys the various kinds of light-induced reactions exploited industrially, the equipment developed, and uses of the photochemical products. Furthermore, the problems encountered in designing a photochemical production plant are discussed for the example of photonitrosation of cyclohexane.     

Photochemistry of various acene based molecules

Photochemistry based on acenes and their derivatives is one of the emerging research areas in the field of polycyclic aromatic hydrocarbons (PAHs). However, due to the increased reactivity of larger acenes towards light and singlet oxygen, it is difficult to precisely control their photochemical reactions. Therefore, the unexpected reactivity of acene-based molecules brings about two challenging topics: how to design stable acenes and how to utilize the photochemistry to design new acene-based functional materials. In this review, we first focus on the mechanism of photochemistry of acenes to theoretically understand how these reactions could have happened. Next, we will give a summary on both acene-based photocyclization and photooxidation reactions.     

How does the skin sense sun light? An integrative view of light sensing molecules

The consensus on the effects of excessive sun exposure on human health has long emphasized the negative effects of solar UV radiation. Nevertheless, although UV radiation has been demonized, less is known about the consequences of sun exposure while using sunscreen, which can lead to high visible light exposure. UV and visible light play key roles in vitamin D synthesis, reduction of blood pressure, among other beneficial effects. In this review, we aim to provide a comprehensive view of the wide range of responses of the human skin to sunlight by revisiting data on the beneficial and harmful effects of UV and visible light. We start by exploring the interaction of photons in the skin at several levels including physical (depth of photon penetration), chemical (light absorption and subsequent photochemical events), and biological (how cells and tissues respond). Skin responses to sun exposure can only be comprehensively understood through a consideration of the light-absorbing molecules present in the skin, especially the light-sensing proteins called opsins. Indeed, many of the cellular responses to sun exposure are modulated by opsins, which act as the “eyes of the skin”.     

Weakly Bound Environment of Molecular Oxygen as a Catalyst of Photooxidation

In the review, the spectral and photochemical manifestations of the catalytic effect of a weakly bound environment on photoprocesses involving oxygen in a gas, solutions, and on the surface are examined in historical sequence. The progress in an experimental study of the nature of supramolecular photochemistry of weakly bound oxygen complexes associated with the use of X–O2 van der Waals complexes generated in molecular beams as a model system is considered. A review of the results of studying supramolecular photochemistry in X–O2 complexes using the velocity map imaging of photofragments is given. The nature of the “dramatic” enhancement of UV absorption in weakly bound oxygen complexes and the mechanism of photochemical processes provided by the “enhanced” absorption are discussed. Available experimental data and conclusions on the nature of absorption bands appearing in weakly bound X–O2 complexes, which give rise to the formation of singlet oxygen and other photooxidation intermediates, are considered.     

A swift dye uptake procedure for dye sensitized solar cells

Solar cells based on swift self-assembled sensitizer bis(tetrabutylammonium)-cis-di(thiocyanato)-N,N'-bis(4-carboxylato-4'-carboxylic acid-2,2'-bipyridine)ruthenium(II) (N719) on double layers of 12 + 4 microm thick nanocrystalline TiO2 films exhibit the incident monochromatic photon-to-current conversion efficiency (IPCE) 90% and show a short circuit current density of 17 mA cm(-2), 750 mV open circuit potential and 0.72 fill factor yielding power conversion efficiencies over 9.18% under AM 1.5 sun. For the first time highest power conversion efficiencies are obtained for dye sensitized solar cells using a swift self-assembled procedure.     

Light as a construction tool of metal nanoparticles: Synthesis and mechanism

The photo-induced synthesis of metal nanoparticles (NPs) was reviewed with a closer look at those based on photochemistry. Recent developments in metal NPs research, photochemistry, and photoprocessing techniques have allowed researchers to devise various photo-induced synthetic strategies to obtain metal NPs under a variety of conditions. We begin by outlining the classical method. The photochemical synthesis of metal NPs including direct photoreduction and photosensitization has been developed to achieve decent yields. We focused on stabilization and functionalization method of NPs in photochemical synthesis, which has enabled us to fabricate a variety of metal nanostructures and composite materials. In addition, we mention an alternative approach, that is, laser ablation at the solid–liquid interface. Some of the most innovative studies dealing with the three-dimensional fabrication of metal NPs are highlighted, together with new directions such as potential applications for a light-driven actuator, bioimaging, and three-dimensional processing. This review is concluded with the future perspectives for the photo-induced synthesis of metal NPs.     

Platinum Alloy Tailored All‐Weather Solar Cells for Energy Harvesting from Sun and Rain

Solar cells that can harvest energy in all weathers are promising in solving the energy crisis and environmental problems. The power outputs are nearly zero under dark conditions for state‐of‐the‐art solar cells. To address this issue, we present herein a class of platinum alloy (PtM_x, M=Ni, Fe, Co, Cu, Mo) tailored all‐weather solar cells that can harvest energy from rain and realize photoelectric conversion under sun illumination. By tuning the stoichiometric Pt/M ratio and M species, the optimized solar cell yields a photoelectric conversion efficiency of 10.38 % under simulated sunlight irradiation (AM 1.5, 100 mW cm^?2) as well as current of 3.90 μA and voltage of 115.52 μV under simulated raindrops. Moreover, the electric signals are highly dependent on the dripping velocity and the concentration of simulated raindrops along with concentrations of cation and anion.