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Photochemistry in Organized and Constrained Media
24 Jun 1991-
TL;DR: Topological connectivity between organized assemblies physical techniques as used in organized assemblies microenvironments as viewed through photophysical probes fractal analysis of photoprocesses in reactive media of complex geometry crystals - unimolecular reactions bimolecular reaction - porous solids (organic and inorganic hosts), nonreactive surfaces, reactive surfaces, liquid crystals, micelles, monolayers, host-guest photochemistry in solution organization in biological systems as discussed by the authors.
Abstract: Topological connectivity between organized assemblies physical techniques as used in organized assemblies microenvironments as viewed through photophysical probes fractal analysis of photoprocesses in reactive media of complex geometry crystals - unimolecular reactions bimolecular reactions - porous solids (organic and inorganic hosts), nonreactive surfaces, reactive surfaces, liquid crystals, micelles, monolayers, host-guest photochemistry in solution organization in biological systems 1 organization in biological systems 2 applications of organized media examples.
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TL;DR: In this article, the authors focus on interfacial processes and summarize some of the operating principles of heterogeneous photocatalysis systems, including the electron transfer and energy transfer processes in photocatalytic reactions.
Abstract: In 1972, Fujishima and Honda discovered the photocatalytic splitting of water on TiO{sub 2} electrodes. This event marked the beginning of a new era in heterogeneous photocatalysis. Since then, research efforts in understanding the fundamental processes and in enhancing the photocatalytic efficiency of TiO{sub 2} have come from extensive research performed by chemists, physicists, and chemical engineers. Such studies are often related to energy renewal and energy storage. In recent years, applications to environmental cleanup have been one of the most active areas in heterogeneous photocatalysis. This is inspired by the potential application of TiO{sub 2}-based photocatalysts for the total destruction of organic compounds in polluted air and wastewaters. There exists a vast body of literature dealing with the electron transfer and energy transfer processes in photocatalytic reactions. A detailed description of these processes is beyond the scope of this review. Here, the authors tend to focus on interfacial processes and to summarize some of the operating principles of heterogeneous photocatalysis. In section 2, the authors first look at the electronic excitation processes in a molecule and in a semiconductor substrate. The electronic interaction between the adsorbate molecule and the catalyst substrate is discussed in terms of the catalyzed ormore » sensitized photoreactions. In section 3, thermal and photocatalytic studies on TiO{sub 2} are summarized with emphasis on the common characteristics and fundamental principles of the TiO{sub 2}-based photocatalysis systems. In section 4, they address the research effort in the electronic modification of the semiconductor catalysts and its effect on the photocatalytic efficiency. Several representative examples will be presented including the Schottky barrier formation and modification at metal-semiconductor interfaces. Some concluding remarks and future research directions will be given in the final section. 160 refs.« less
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TL;DR: In this article, the CMC values corresponding to the surfactants sodium dodecyl sulfate, tetradecyl trimethylammonium bromide and polyoxyethylene,9-dodecyl ether determined in the absence and presence of electrolytes and nonelectrolytes are reported.
Abstract: The laboratory experiments described in this work present the CMC-determination of some surfactants by following three different methods, which require the use of the very common techniques in physical chemistry laboratories, such as UV-Vis spectroscopy, luminescence spectroscopy, and electrical conductivity.In performing these experiments, the CMC of a surfactant is determined by measuring a change (i) in the UV-Vis spectra of benzoylacetone, (ii) in the fluorescence emission spectra of pyrene monomers, and (iii) in the electrical conductivity of an ionic-surfactant solution, as the concentration of the surfactant increases.The CMC values corresponding to the surfactants sodium dodecyl sulfate, tetradecyl trimethylammonium bromide and polyoxyethylene,9-dodecyl ether determined in this work following the three indicated methods and in the absence and presence of electrolytes and non-electrolytes are reported.
594 citations
TL;DR: The controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules is reported, which modifies the structures of these molecules without affecting their crystallinity.
Abstract: Considerable effort is being devoted to the fabrication of nanoscale devices1. Molecular machines, motors and switches have been made, generally operating in solution2,3,4,5,6,7, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required8. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure9. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion–reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage10. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches11,12.
474 citations
TL;DR: It is shown that the fluorescence decay time is fluctuating during the investigation leading to a multiexponential decay even for a single nanocrystal, consistent with a model of fluctuating nonradiative decay channels leading to variable dynamic quenching processes of the excited state.
Abstract: We present fluorescence decay measurements of single ZnS covered CdSe nanocrystals. It is shown that the fluorescence decay time is fluctuating during the investigation leading to a multiexponential decay even for a single nanocrystal. In combination with measurements of the fluorescence blinking behavior we find that a high fluorescence intensity is correlated with a long fluorescence decay time. This is consistent with a model of fluctuating nonradiative decay channels leading to variable dynamic quenching processes of the excited state.
442 citations