Showing papers in "Journal of Photochemistry and Photobiology C-photochemistry Reviews in 2003"
TL;DR: In this paper, a novel strategy for artificial photosynthesis where porphyrins and fullerenes are assembled as building blocks into nanostructured artificial photosynthetic systems by the help of self-assembled monolayers was proposed.
Abstract: We have proposed a novel strategy for artificial photosynthesis where porphyrins and fullerenes are assembled as building blocks into nanostructured artificial photosynthetic systems by the help of self-assembled monolayers. Photodynamical studies on porphyrin–fullerene-linked systems revealed that fullerenes accelerate photo-induced electron transfer and charge-shift and slow down charge recombination, which is in sharp contrast with the modalities of conventional two-dimensional aromatic acceptors such as quinones and imides. We proposed and demonstrated, for the first time, that such electron transfer properties are attributable to the small reorganization energies of fullerenes, which make it possible to optimize artificial photosynthetic multistep charge separation. The multistep electron transfer strategy was combined with our finding that fullerenes have small reorganization energies, which are well-suited for the construction of light energy conversion systems as well as artificial photosynthetic models. Highly efficient photosynthetic energy and electron transfers were realized at gold and indium–tin oxide (ITO) electrodes modified with self-assembled monolayers of porphyrin–fullerene-linked systems. Porphyrin-modified gold nanoclusters were found to have potential as artificial photosynthetic materials and photonic molecular devices. These results provide basic principles and concepts for the development of nanostructured artificial photosynthetic materials as well as molecular devices.
385 citations
TL;DR: In this paper, the progress in all of these areas will be reviewed thoroughly, including the early stage of the research, the band structure, photochromic mechanism and the behavior of the oxide.
Abstract: Molybdenum oxide can exhibit pronounced photochromism and thus might act as an excellent photonic material for a number of technical applications. In the early stage of the research, the attention was focused mainly on the (band) structure, photochromic mechanism and the behavior of the oxide. Later, many investigations were carried out on the factors that might influence the photochromic performance. At the same time, the photochromic response has been extended from UV light to visible light. In this review, the progress in all of these areas will be reviewed thoroughly.
258 citations
TL;DR: In this article, a review of the photocatalytic reactivities and their mechanisms of various Ti-based photocatalyst for various different types of reactions in order to achieve as highly efficient reactivities as possible is presented.
Abstract: Scientific studies of TiO 2 as photocatalyst started more than two and half decades ago. High efficiency in the photocatalytic reactions was achieved by increasing the surface area of the photocatalyst by supporting fine TiO 2 particles on porous materials. Among various supports, zeolites seem to be an attractive candidate. So, the present review focuses on the photocatalytic reactivities and their mechanisms of various Ti-based photocatalysts for various different types of reactions in order to achieve as highly efficient photocatalytic reactivities as possible.
203 citations
TL;DR: In this article, the authors reviewed the topics of photochemistry within zeolites and provided some comments for future studies, focusing on transient spectroscopic studies, which have shown to be a powerful technique for mechanistic investigations in solid systems.
Abstract: The past decade has witnessed increasing activity in photochemistry within zeolites. This article critically reviews the topics of such activities and provides some comments for future studies. Particular emphasis is placed on transient spectroscopic studies, which have shown to be a powerful technique for mechanistic investigations in solid systems. As a host material for organic species, zeolites are another promising candidate for modifying the photophysics and photochemistry of a given species. Besides, photochemical reactions can be pursued in zeolites and provide product distributions considerably different from those in solutions. Accordingly, photochemistry has enjoyed a great benefit from zeolite materials and zeolite science. In return, photochemical techniques can provide pieces of useful information on the fundamental issues of zeolite science such as adsorption and diffusion of molecules within the zeolite. Thus, we can expect further development in this area if this cooperative relationship continues. In this article, we mainly describe mechanistic aspect of photochemical reactions. Issues associated with experimental techniques are also reviewed.
187 citations
TL;DR: In this paper, the photocatalytic reactivity of transition metal oxides and ions in their efficiency and selectivity were found to depend strongly on their local structures, which are controlled by the unique and restricted framework structures of zeolites.
Abstract: Transition metal oxides (Ti, V, Mo, Cr) incorporated within the framework of zeolites as well as transition metal ions (Cu+, Ag+, Pr3+) exchanged within the zeolite cavities were found to exhibit high and unique photocatalytic activities for various reactions such as the decomposition of NOx (NO, N2O) into N2 and O2 or the reduction of CO2 with H2O to produce CH4 and CH3OH. Various in situ spectroscopic investigations of these catalytic systems using photoluminescence, X-ray absorption fine structure (XAFS) (X-ray absorption near edge structure (XANES) and Fourier transform of EXAFS (FT-EXAFS)), electron spin resonance (ESR), FT-IR, etc. revealed that the photo-excited states of these transition metal oxides or ions play a vital role in these photocatalytic reactions. The photocatalytic reactivity of these oxides and ions in their efficiency and selectivity were found to depend strongly on their local structures, which are controlled by the unique and restricted framework structures of zeolites.
173 citations
TL;DR: In this article, highly polarized polyene aldehydes attached to azulene at C-1 as a π-electron donating end group were successfully incorporated into bacterioopsin to generate NIR absorbing bacteriorhodopsin pigment analogs.
Abstract: In this review, we summarize the work carried out at the University of Hawaii on the highly colored, non-alternant hydrocarbon azulene. Through systematic perturbation of the HOMO and LUMO molecular orbitals, we showed that the characteristic azure color can be changed in a manner that covers the entire visible spectrum based on this single chromophore. Some of the modified azulenes exhibit unusual excited state properties: reversal of energy gap of low lying excited states, unprecedented high fluorescence yield, and long fluorescence lifetime for an upper state in condensed media. Highly polarized polyene aldehydes attached to azulene at C-1 as a π-electron donating end group have been successfully incorporated into bacterioopsin to generate NIR absorbing bacteriorhodopsin pigment analogs—the longest wavelength absorbing analog with λ max =830 nm. Azulene-containing donor–acceptor and symmetrical dye chromophores were synthesized and their excited state absorption spectra, and other properties determined. Non-linear optical properties were also examined. The azulenic dye chromophores are reverse saturable absorbers and are potentially useful for optical limiting applications.
66 citations
TL;DR: In this paper, recent understandings of the urban atmosphere are briefly presented, focusing on NOx (NO and NO2), NO3 and HOx (OH and HO2), which are the key species for photochemical ozone production in the urban air.
Abstract: In this review article, recent understandings of the urban atmosphere are briefly presented, focusing on NOx (NO and NO2), NO3 and HOx (OH and HO2), which are the key species for photochemical ozone production in the urban air. For NOx chemistry, relationship between NOx and HOx, and photostationary state (PSS) of the conversion between NO and NO2 are introduced with examples of recent research. Chemistry of nitrate radicals in the nighttime is also introduced. In addition, recent and representative techniques for the measurements of reactive nitrogen species in the troposphere are presented. As for HOx radicals, important formation and loss processes and measurement methods developed recently are introduced. Recent campaign-based observations of HOx radicals in the troposphere are also presented.
60 citations
TL;DR: An overview of the application of time-resolved electron paramagnetic resonance (TREPR) to the study of excited triplet states can be found in this article, where the authors discuss the properties of non-phosphorescent triplets, various interactions (configurational, vibronic and spin-orbit) and triplet properties, molecular distortions, and triplets related to excited-state proton transfer.
Abstract: In this review, we present an overview of the application of time-resolved electron paramagnetic resonance (TREPR) to the study of excited triplet states. After a brief discussion of background and experimental methods, triplet properties clarified by TREPR are reviewed to show how TREPR provides rich information about electronic and molecular structures and dynamic properties of the lowest excited triplet states. The review includes discussion of the properties of non-phosphorescent triplet states, various interactions (configurational, vibronic and spin–orbit) and triplet properties, molecular distortions, and triplet states related to excited-state proton transfer. For each topic, typical examples are taken mainly from work carried out in the authors’ laboratories in Kyoto and Sendai over the last two decades. Finally, recent new advances are reviewed briefly by focusing attention on two topics: excited triplet states in liquid solution and multiplet excited states generated by triplet–radical interactions.
41 citations
TL;DR: In this paper, the most common quantum chemical approaches for estimation of each term and show that it is possible to arrive at a realistic estimate of the overall rate of electron-transfer in tripartite supermolecules of general type donor-bridge-acceptor (D-B-A).
Abstract: Electron-transfer processes, and especially light-induced electron-transfer reactions, play an extremely important role in natural and artificial energy transduction. Following many decades of intensive theoretical and experimental study, it is now opportune to explore electron-transfer processes by way of modern computational chemistry. In essence, this requires the meaningful calculation of those thermodynamic parameters that combine to control the rate of electron-transfer between remote donor and acceptor species. The most important parameters are the nuclear and solvent re-organisation energies, the electronic coupling matrix element, the change in Gibbs free-energy and the activation energy change accompanying electron-transfer. Clearly, the surrounding environment has to be taken into account. Restricting attention to intramolecular electron-transfer in tripartite supermolecules of general type donor–bridge–acceptor (D–B–A), it is possible to compute each of the required thermodynamic properties from first principles. We examine here the most common quantum chemical approaches for estimation of each term and show that it is possible to arrive at a realistic estimate of the overall rate of electron-transfer. Attention is focused on readily accessible computational methodology.
37 citations
TL;DR: In this paper, the photodissociation dynamics of carboxylic acids carried out in our laboratory are investigated by mapping the energy partitioning in the nascent photoproduct OH using laser-induced fluorescence spectroscopy, and a high percentage of the available energy is partitioned into the product translational state, indicating the presence of an exit barrier in the dissociative potential energy surface.
Abstract: In this review article, recent studies on the photodissociation dynamics of carboxylic acids carried out in our laboratory are presented. The dynamics are investigated by mapping the energy partitioning in the nascent photoproduct OH using laser-induced fluorescence spectroscopy. To understand the effect of the nature of the CC bond on the dissociation dynamics, both saturated (acetic) as well as unsaturated (acrylic and propiolic) carboxylic acids are investigated. In all of the carboxylic acids studied, a high percentage of the available energy is partitioned into the product translational state, indicating the presence of an exit barrier in the dissociative potential energy surface. Based on the energy partitioning, the quantum yield and the OH formation rate, the photoexcitation dynamics of carboxylic acids are revealed.
30 citations
TL;DR: In this article, a review of recent advances in chemical applications of optical trapping of single microparticles in solution, with special reference to microspectroscopy (absorption, fluorescence, and Raman spectroscopy), interfacial processes across microdroplet/solution interfaces, and photochemical reactions in microdroplets is presented.
Abstract: This paper reviews recent advances in chemical applications of optical trapping of single microparticles in solution, with special reference to microspectroscopy (absorption, fluorescence, and Raman spectroscopy), interfacial processes across microdroplet/solution interfaces, and photochemical reactions in microdroplets. After describing the principles and experimental setups of optical trapping of single microparticles, recent topics of chemical applications of the techniques are described. The work on optical trapping-electrochemical measurements of single microdroplets is also summarized. In particular, this review focuses on demonstrating the characteristics of chemical processes in micrometer dimensions, i.e., “microchemistry”.
TL;DR: In this article, the role of stable dimer cation formation and its relation to the rapid hole transfer (HT) process is discussed on the basis of the experimental results for the photo-induced electron transfer dynamics in the poly(1-vinylpyrene) system, where effective dimer Cation formation occurs.
Abstract: Primary processes of photoinduced electron transfer (ET) dynamics in aromatic vinyl polymers, such as charge separation, charge recombination, and hole migration reactions, in solution, solid, and adsorbed systems are reviewed. The application of time-resolved transient absorption spectroscopy and dichroism measurements clearly demonstrates that the electron transfer dynamics in aromatic vinyl polymers in solution phase are well described by a simple scheme in which the cation migrates continuously along pendant aromatic moieties in a polymer chain and the charge recombination at the initial position of the charge separation. Dependence of the hole transfer (HT) rate constants on the size of the aromatics and the solvent polarity suggest that the delocalization of the cationic state over several aromatic side groups takes on an important role in the rapid HT processes. The role of stable dimer cation formation and its relation to the rapid HT process are discussed on the basis of the experimental results for the ET dynamics in the poly(1-vinylpyrene) system, where effective dimer cation formation occurs. For photoconductive amorphous solid PVCz films doped with electron acceptors, the direct investigation of the primary processes of the electron transfer dynamics also reveal that the hole migration from the cation state of the carbazolyl moiety (Cz) to neighboring Cz’s in solid films takes place in the nanosecond time region. An extremely long-lived charge-separated state (>8 h) was attained due to the charge shift reactions in a PVCz system co-adsorbed with an electron acceptor on a macroreticular resin. On the basis of these direct measurements, the mechanism of the primary events of the photoinduced electron transfer processes coupled with photoconduction in the aromatic vinyl polymer and related molecular systems are discussed from the viewpoint of the elementary ET reactions.
TL;DR: In this paper, the authors examined the nature of these dust clouds and then described some basic aspects of heterogeneous photocatalysis, a methodology that has been shown useful in transforming organic substrates into smaller molecules and in the synthesis of potential biomolecules.
Abstract: Heterogeneous reactions occur on solid photocatalyst particles of semiconductors and dielectric materials. When irradiated with suitable UV/visible light energy these particles generate electrons and holes, which on the surface are poised to undergo reductive and oxidative chemistry with a variety of organics and light gases. Various such particles have been identified in Interstellar Space, specifically in molecular–dust clouds, comets and meteorites. In this article, we examine briefly the nature of these dust clouds and then describe some basic aspects of heterogeneous photocatalysis, a methodology that has been shown useful in transforming organic substrates into smaller molecules and in the synthesis of potential biomolecules. Various types of gas/solid heterogeneous reactions involving mostly small molecules in gas/solid systems find a relationship to abiogenesis. For example, the decomposition of H2O and CO2 in the presence of CH4 yields H2CO; methane is photoconverted into ethane, propane, ethylene and other hydrocarbons and is photooxidized to alcohols and carbon dioxide; photofixation of CO2 occurs to yield formaldehyde, formic acid, methanol and methane; and finally photofixation of molecular nitrogen N2 can take place to produce NH3 and N2H2. Not least is the synthesis of glycine, alanine, aspartic acid and serine from CH4 and NH3 over platinized titania. The relevance of heterogeneous photocatalysis to abiogenesis is discussed. It is argued that the physical conditions available in the interstellar medium are propitious to generate such biomolecules as amino acids and others, albeit this assertion necessitates laboratory simulations. Recent laboratory experiments involving very simple photoinduced processes are encouraging.
TL;DR: In this article, the contribution of spin chemistry (in particular, magnetic resonance-related chemistry) to the photochemical field is briefly introduced, and the most important physical conclusions are the introduction of the spin phase relaxation termed singlet-triplet (S − T ) and triplet-triplets (T - T ) dephasing, instead of the traditional concepts of longitudinal (T 1 ) and transversal relaxations (T 2 ).
Abstract: In this review, the contribution of spin chemistry (in particular, magnetic resonance-related chemistry) to the photochemical field is briefly introduced. First, the development of a time-resolved EPR method and its significant application to radical-related physical phenomena and chemical reactions are presented. Second, a reaction-control method by means of electron spin operations is introduced, and several reaction yield-detected magnetic resonance (RYDMR) methods are presented as applications of this concept. One of the most important physical conclusions is the introduction of the concept of “spin phase relaxation” termed singlet–triplet ( S – T ) and triplet–triplet ( T – T ) dephasing, instead of the traditional concepts of longitudinal ( T 1 ) and transversal relaxations ( T 2 ). The effects of strong microwave power on the RYDMR spectrum and time-domain data are analyzed according to this concept. Furthermore, a new detection method is introduced, termed “photoconductivity detected magnetic resonance” (PCDMR), which is applicable exclusively to the system of charge transfer reactions.
TL;DR: In this paper, the absorption and photodissociation of O2 in the UV wavelength region, which result in O3 formation in the atmosphere, are investigated, and the relevant absorption is due to Herzberg states.
Abstract: The absorption and photodissociation of O2 in the UV wavelength region, which result in O3 formation in the atmosphere, are investigated. The relevant absorption is due to Herzberg states, whose forbidden character is partly mitigated under the pressurized condition. The formation of odd oxygen species under pressurized conditions is possible even in the wavelength region longer than the dissociation threshold at 242.4 nm, and its mechanism is discussed. The latter is responsible for the initiation of the laser-induced oxidation of hydrocarbons in hydrocarbon/O2/supercritical CO2 mixtures at 248 nm.