79145 - Molecular and Supramolecular Photochemistry

Course Unit Page

SDGs

This teaching activity contributes to the achievement of the Sustainable Development Goals of the UN 2030 Agenda.

Quality education Affordable and clean energy Responsible consumption and production

Academic Year 2021/2022

Learning outcomes

At the end of the course, the student knows the theoretical bases of photophysics and photochemistry. In particular, the students is able to: - analyze intra- and intermolecular processes involving excited states; - understand the working principle and use of the simplest photochemical techniques; - evidence the possible applications of photochemistry in the industrial field, for energy conversion, and luminescent sensors; - use the simplest photophysical and photochemical techniques both in steady-state and time-resolved regime, usually employed to characterize molecular and supramolecular systems.

Course contents

PART 1: MOLECULAR AND SUPRAMOLECULAR PHOTOCHEMISTRY (Prof. Paola Ceroni)

Prerequisites: knowledge of physical chemistry bases for the description of atoms and molecules. Basic knowledge of symmetry groups and their use in chemistry.

Programme: the course is designed so that the student will acquire basic concepts of photochemistry and the capacity to tackle real experimental systems. Please find below more details.

1. Introduction : what is photochemistry; history of photochemistry with particular reference to Giacomo Ciamician. Excited states as new chemical species: different energy, lifetime, geometry, dipole moment, redox and acid/base properties, reactivity. Deactivation processes of electronic excited states: rate constants, efficiencies, quantum yields. Lifetimes of an electronic excited state: definition and relation to deactivation rate constants.

2. State diagram of atoms and molecules: orbitals, electronic configurations and excited states of atoms (e.g., oxygen) and diatomic and polyatomic molecules (e.g., dioxygen, formaldehyde, coordination compounds). Outlines of symmetry group theory.

3. Radiative and radiationless processes: molecular wavefunctions and Born-Oppenheimer approximation. Probability and selection rules for radiative transition of absorption, spontaneous and stimulated emission, and for radiationless transitions. Frank-Condon principle, Jablonski diagram: approximation and information that can be obtained from it. Correlation between absorption/emission spectra and the corresponding Jablonski diagram (e.g., benzophenone, naphthalene). Potential energy curves and surfaces for ground and electronic excited states of simple molecules.

4. Bimolecular quenching processes involving electronically excited states: Stern-Volmer equation, excimers and exciplexes. Catalyzed deactivation, photoinduced energy- and electron-transfer. Examples of quenching experiments by measurements of excited state lifetimes and emission quantum yields: static and dynamic quenching.

4.1 Electronic energy transfer: Coulombic and exchange mechanisms; spin selection rules and distance dependence. Applications of sensitization and quenching processes.

4.2 Photoinduced electron transfer: redox potential of electronic excited states. Examples of photocatalysis, conversion of light into chemical energy and vice versa (chemiluminescence and ectrochemiluminescence).

5. Laser: principles of lasers based on 3 or 4 levels. Examples of the most commonly used lasers. Applications in photochemistry, medicine, material science, memories. Basic concepts of time-resolved measurements for identifying transient species (laser-flash photolysis)

6. Excited state properties: different energy, lifetime, geometry (pulsed X-ray techniques), dipole moment (solvatochromic dyes and TICT compounds), reactivity, redox properties, acid-base properties (Förster cycle)

7. Supramolecular photochemistry: definition of a supramolecular system, nature of the interactions between the component units and kinetics of quenching processes.

8. Electron transfer processes in supramolecular systems: Marcus and superexchange theories for electron transfer, effect of the bridge; selected examples from artificial and natural systems.

9. Molecular wires and switches for photoinduced electron and energy transfer: systems based on metal complexes, organic compounds, and DNA. Molecular switches operated by a photochemical mechanism. Plug-socket systems and elongation cables.

10. Photoactive dendrimers and QDs: light-harvesting antennae, sensors with signal amplification. Basic concepts of the photophysics of quantum dots (QDs).

  




PART 2: PHOTOCHEMICAL TECHNIQUES (Prof. Marco Montalti)

Fast survey on electronic absorption spectroscopy (technics and instrumentation) - Relation among absorption bands and electronic transitions - Emission spectroscopy - technics and instrumentation - emission and excitation spectra - interferences (light and raman scattering, harmonics) - corrected spectra - emission lifetimes determination (instrumentation)- Relation among emission bands and electronic transitions - Irradiation technics (lamps, filters, actinometers, etc.) - sensititation and quenching - transient absorption spectroscopy (technics and instrumentation).

 

PART3: Laboratory of Photochemistry (Prof. Serena Silvi)

Spectroscopic characterization of some compounds by practical determination of their absorption and emission spectra, emission lifetimes, photochemical reactivity, reaction and emission quantum yields, actinometers. Moreover systems exhibiting sensitization and quenching will be analyzed.

Readings/Bibliography

Prof. Paola Ceroni

Lecture notes on the teacher web site .

- V. Balzani, P. Ceroni, A. Juris, Photochemistry and Photophysics: Concepts, Research, Applications, Wiley-VCH, 2014.

- P. Klán, J. Wirz, Photochemistry of Organic Compounds, Wiley 2009.

- V. Balzani, A. Credi, M. Venturi: : Molecular Devices and Machines. Concepts and Perspectives for the Nanoworld, 2° edizione, Wiley-VCH, 2008

 

Prof. Marco Montalti

"Chemistry and light", Paul Suppan, Cambridge, The Royal Society of Chemistry, 1994. Copies of the transparencies used in the class

 

Prof. Serena Silvi

" The Exploration of Supramolecular Systems and Nanostructures by Photochemical Techniques , P. Ceroni Ed., Springer, Lecture Notes in Chemistry, Vol. 78, Ch.1, p. 1-20, Heidelberg, Germany, 2012, ISBN 978-94-007-2041.

Teaching methods

Prof. Paola Ceroni: the course consists of 8CFU of lectures and discussions on principles of photochemistry and photophysics, accompanied by examples of practical problems which a student may encounter in the laboratory.

Prof. Marco Montalti: class lessons: theoretical lessons (2 CFU) will be devoted to the presentation of the various technics usefull to study the photochemical and photophycal behaviour of compounds.

Prof. Serena Silvi: the lectures (1 CFU) will present the laboratory exercises; laboratory experiences (1 CFU) are aimed at reaching the manual ability and the necessary knowledge to perform a photochemical study.

All students must attend Module 1, 2 [https://www.unibo.it/en/services-and-opportunities/health-and-assistance/health-and-safety/online-course-on-health-and-safety-in-study-and-internship-areas] online, while Module 3 on health and safety is in class. Information about Module 3 attendance schedule is available on the website of your degree programme.

Assessment methods

Oral examination for each of the parts in which the course is divided (Prof. Ceroni, Montalti and Silvi) and reports on the practical lab exercises (Silvi). The examination will verify that the student has acquired knowledge of photochemistry and the capacity to tackle real experimental problems related to photoactive systems.

The final mark is calculated as the weighted average on the basis of the credit numbers of the three parts: Part 1, Prof. Ceroni (8 CFU) Part 2, Prof. Montalti (2 CFU), Part 3, Prof. Silvi (2 CFU).

Teaching tools

Power Point slides, blackboard and simple experiments in the classroom.

spectrophotometers, spectrofluorometers, lasers, single photon counting and transient spectroscopy instrumentations for laboratory experiences.

Office hours

See the website of Paola Ceroni

See the website of Marco Montalti

See the website of Serena Silvi