PHOTOCHEMISTRY
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- Versione italiana
- Academic year
- 2022/2023
- Teacher
- MIRCO NATALI
- Credits
- 6
- Didactic period
- Primo Semestre
- SSD
- CHIM/03
Training objectives
- The course aims at a comprehensive overview of the processes involving light and chemical systems, from simple molecules, to complex supramolecular systems, to specific biological systems, with perspective applications including solar energy conversion, molecular electronics, and photonics. The student will learn on the description of electronically excited states and on the main physical and chemical processes that lead to their deactivation as well as on the experimental methods that allow for the characterization of such photochemical processes. The student will be able to predict the photophysical and photochemical processes involving molecular systems on the basis of the electronic structure and interpret the experimental data arising from the respective photochemical characterization.
Prerequisites
- Basic notions of inorganic chemistry, physical chemistry, and spectroscopy are mandatory.
Course programme
- The course consists of 48 hours frontal lectures covering the following topics:
Light: Dual nature of light. Electromagnetic spectrum.
Electronic states: Group theory, molecular symmetry, and point groups. Molecular orbital (MO) theory. Born-Oppenheimer approximation. Electron configurations. Electronic states in closed-shell organic molecules. Electronic states in open-shell molecules. Coordination compounds. Vibrational levels.
Light absorption: Transition moment. Selection rules: symmetry and spin. Franck-Condon principle. Structure of absorption bands.
Photophysics: Radiative deactivation. Vibrational relaxation. Fluorescence and phosphorescence. Franck-Condon factors and absorption/emission relationships. Excited-state distortion and Stokes shift. Radiationless transitions. Fermi golden rule. Internal conversion and intersystem crossing. El-Sayed’s rule. Heavy atom effect. Franck-Condon factor. Energy-gap law and distortion. Deuteration effects. Kasha’s rule. Kinetic aspects. Description of the photophysical processes in organic molecules and coordination compound of photochemical relevance.
Photochemistry: Chemical processes in excited states. Adiabatic reactions. Diabatic reactions, avoided crossing and conical intersection. Correlation diagrams for molecular orbitals and states. Dissociation of sigma bonds. Twisting around "pi" bonds. Pericyclic reactions.
Bimolecular excited-state processes: Kinetic aspects and Stern-Volmer kinetics. Electronic energy transfer. Radiative energy transfer (“trivial” energy transfer). Non-radiative energy transfer. Quenching and sensitization. Spectral overlap. Coulombic and exchange mechanisms. Photoinduced electron transfer. Redox properties of excited states. Kinetic models and Marcus theory. Electronic factors. Superexchange mechanism. Charge separation and recombination. Chemiluminescence. Excited state proton transfer. Forster cycle.
Photochemistry in biological systems: Photons as energy quanta. Photosynthesis. General aspects of solar energy. Natural photosynthesis. Antennae. Reaction centers. Architecture, thermodynamics, kinetics. Towards an artificial photosynthesis. Artificial reaction centers and antennae. Multi-electronic catalysis. Proton-coupled electron-transfer (PCET). Photons as information bits. Vision. Photoreceptors.
Spectroscopic techniques for application in photochemical studies. Spectrophotometer, spectrofluorometer. Emission and excitation spectra. Emission quantum yield. Experimental aspects. Stimulated emission, Einstein theory of emission, LASER. Time-resolved spectroscopy techniques. Didactic methods
- The course consists of 48 h frontal lectures in which presentation slides are used.
Recorded lectures will be available at the following classroom with code: 7vhdl5r Learning assessment procedures
- The aim of the final exam is to check the level of knowledge acquired on the topics covered. The test consists of an oral examination with at least 3 open questions.
Reference texts
- Presentation slides are available for the students.
The study must be integrated using the following books:
"Photochemistry and Photophysics, Concepts, Research, Applications" V. Balzani, P. Ceroni, A. Juris, Wiley-VCH,Verlag 2014
"Supramolecular Photochemsitry" V. Balzani, F. Scandola, Horwood, 1991
Further readings:
Concerning the part of the course covering the experimental aspects: "Manuale del fotochimico. Tecniche e metodologie" L. Moggi, A. Juris, M. T. Gandolfi, Bononia University Press, 2006.
Concerning the part of the course covering the photchemical reactions: "Modern molecular photochemistry of organic molecules" N. J. Turro, V. Ramamurthy, J. C. Scaiano, University Science Books, 2010.
