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Recent research of the Laboratory of Photochemistry is concerned mainly with the problems of mechanisms and kinetics of several kinds of photoreactions in homogeneous media and in organized molecular systems.
In the Laboratory there are the following projects:
Electron transfer mechanisms of exciplex and excimer formation reactions kinetics were studied by fluorescence spectroscopy and flourescence kinetics methods.
Reactivity of exciplexes and their role in photoreaction kinetics were investigated. Rules for effects of exciplex and excimer formation on the reactivity of excited molecules were proposed.
Non-relaxed states were found to be important for photoreactions, which are supposed to follow electron transfer or exciplex mechanisms.
Electron tunneling mechanism of photoinduced electron transfer in frozen glassy solutions was proved.
Exciplex mechanism of fluorescence quenching in polar media was put forward, quite different from the convential mechanism of direct complete electron transfer in encounter complex. The latter seems to be valid only for strongly exergonic electrn transfer reactions (at diffusion limit) and cannot explain observed experimental features of fluorescence quenching by electron donors and acceptors in kinetic region.
Kinetics of electron transfer photoreactions in organized molecular systems was studied. Effects of the interface reactant diffusion were found to determine the type of kinetic laws (discrete concentration distribution over microreactors, or average conce ntration in the microphase) for photoreactions in microheterogeneous systems.
Chain ion-radical reactions of
photosubstitution in aromatic compounds
Kinetics and mechanisms of photosubstitution reactions in aromatic ring and in &alpha-position to aromatic ring studied
Electrophylic photosubstitution in aromatic ring were discovered.
The problem of adiabaticity of heterolytic reactions of excited aromatic molecules was analyzed.
Adiabatic heterolytic photodissiciation reactions of carbon atom of excited aromatic ring were found.
Effects of excited molecules structure and of the media on the adiabaticity of photoreactions are analyzed
Induced electronic energy degradation in the reaction complex of heterolytic reactions of excited molecules was found.
The mechanisms of the induced excitation energy degradation were proposed.
Nucleophylic photosubstitution reactions in aromatic ring were investigated. Several radical-ion chain mechanism were found for "nucleophylic" photosubstitution.
Mechanisms and kinetics of photoinitiation of radical-ion chain substitution reactions in aromatic compounds were studied. These chain reactions may have very high quantum yields (up to 10^2) and electron transfer intermediate stages are involved.
A knowledge of the general behavior and of main laws of proton transfer reactions in homogeneous and organized molecular systems is necessary to understand the mechanisms of natural proton transport and to design model and artificial molecular devices. In vestigations of excited state proton transfer reactions supply quite important and unique information on the local structure and dynamics of organized molecular systems.
Spectroscopy and kinetic study of proton transfer photoreactions revealed the nature of the effects of the states of the molecular structure on the acidity and basicity of the excited states of organic molecules, the dependence of rate constants on the fr ee energy of the reactions, molecular charges, and hydrogen bonding.
Chemical and dynamic effects of the media were found in energetics and in kinetics of proton transfer photoreactions.
Photoelectrochemical effect at the interface of immiscible electrolyte solutions was discovered. Electrical current was shown to be induced under the illumination of the interface of immiscible electrolyte solutions (e.g. 1,1-dichlorethane solution of tet rabuthylammonium tetraphenylborate aqueous solution of sodium chloride) in several electron donor - acceptor systems with quantum yield up to 10%.
The theory of the photoelectrochemical effect at the interface of immiscible electrolyte solutions was developed.
Professor Edwin Haselbach, University of Fribourg, Inst. for Physical Chemistry
Dr. Eric Vauthey , University of Fribourg, Inst. for Physical Chemistry
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