Master Course Dynamics of intra- and inter molecular photochemical reactions and photophysical processes Content Absorption of electromagnetic radiation in the ultraviolet and visible range, sunlight. Properties of molecules: energy, reactivity and structure in singlet and triplet electronic excited states, Jablonski diagram. Photochemical and thermal reactions, comparative analysis of mechanisms and rates. Time scales and mechanisms of fast and ultrafast fundamental processes (radiative decay, rotational motion, vibrational motion), physical processes (internal conversion and intersystem crossing, vibrational relaxation, collisions in liquids), chemical reactions (electron and proton transfer, abstraction and dissociation reactions, isomerization reactions). Potential energy surfaces of the ground state (S0) and excited state (S1 or T1) and of various processes following the initial excitation. Structure (geometry) changes in the excited state as an important path of deactivation in radiationless (nonradiative) physical processes (conical intersection) and photochemical reactions (isomerization). Relation between physical processes and chemical reactions: rotation and isomerization reaction, vibration and dissociation reaction. Primary and secondary, reversible (cage effect) and irreversible photochemical reactions. Short-lived species formed in photochemical reactions: radicals, radical-ions, dimers, complexes. The effects of concentration of the substance studied, of the solvent properties and of the wavelength of the radiation absorbed. Energy transfer processes, sensitizers and quenchers. Storage and conversion of solar energy. Instruments and methods of investigation of photophysical processes and photochemical reactions. Steady-state and time-resolved (laser) absorption and emission spectroscopy. The conditions for the correct measurement of the absorption and emission spectra and determination of the quantum yield and lifetime. Laboratory
Application of time-resolved emission spectroscopy for lifetime determination of polyatomic molecules in an electronic excited state, using the TCSPC method (for antracene in cyclohexane, xanthione in perfluoro-1,3-dimethylocyclohexane and in hexane and 6,7-dimethyloalloxazine in acetonitrile).
Properties of chemical and biological systems in electronic excited states. Application of transient absorption spectroscopy with laser excitation to determination of quantum yield of the triplet state formation (for T1-antracene, using T1-benzophenone as standard).
Dynamics of monomolecular and bimolecular processes. Influence of concentration and viscosity of the solvent on S1-pyrene decay rate, its fluorescence quantum yield, and efficiency of S1-excimer formation.
Application of sensitization and/or quenching processes in studies of mechanism and dynamics of photophysical and photochemical processes, using time-resolved and steady-state spectroscopy. Stern-Volmer equation (T1-carboxybenzophenone as a sensitizer and 2-propanol as a quencher).
Understand the properties of molecules in electronic-excited states as compared to the ground state; understand the effect of these properties, in particular of the high energy of the respective excited states, on the exceptionally high reactivity and structural changes of the excited molecules. Know the most important types of photophysical processes and photochemical reactions. Acquire familiarity with the spectroscopic methods used in photochemical and photophysical studies, including the steady-state and time-resolved absorption and emission spectroscopy and their application in research and analytical work in chemistry, physics, biology and medicine, in both routine and novel studies.
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