66836 - Molecular and Supramolecular Photochemistry

Academic Year 2018/2019

  • Docente: Paola Ceroni
  • Credits: 12
  • SSD: CHIM/03
  • Language: Italian
  • Moduli: Paola Ceroni (Modulo 1) Marco Montalti (Modulo 2)
  • Teaching Mode: Traditional lectures (Modulo 1) Traditional lectures (Modulo 2)
  • Campus: Bologna
  • Corso: Second cycle degree programme (LM) in Photochemistry and molecular materials (cod. 8026)

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.

Attendance to the lectures is not mandatory.

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., water, 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 electrochemiluminescence).

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.

6. Equipment for photochemical reactions: irradiation sources (incandescent or arc lamps, lasers), interference or cut-off filters. Chemical actinometry: principles, and experimental aspects.

7. Spectrofluorimetry: block diagrams of the instrumentation, main components. Emission and excitation spectra, and lifetimes in the m s-s time scales. Brief discussion on single molecule fluorescence: principles and applications of confocal and wide-field microscopy.

8. Time-resolved measurements of absorption and emission spectra: conventional laser flash photolysis and “pump-probe” technique. Block diagram, main components, excited state lifetimes in the ps-ns time range.

9. Overview of  photochemistry applications   (a) in the biological and medical field (vision, protection against biological damages (sunscreens), photodynamic therapy); (b) to ecological issues (photosmog, photodegradation of pollutants); (c) in the industrial field  (photochromic materials, optical stabilizers and brighteners, LED, photovoltaic cells).

10. Supramolecular photochemistry: definition of a supramolecular system, nature of the interactions between the component units. Quenching processes, Marcus and superexchange theories for electron transfer, energy transfer processes.

11. 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.

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

13. Natural and artificial photosynthesis: antenna systems for energy transfer and reaction center for photoinduced electron transfer process in Nature. Artificial photosynthesis (splitting of water by solar energy): artificial antenna and reaction center model systems, photoelectrochemical cells.

14. Molecular machines operated by light: basic principles, energy inputs and signals. Rotary and linear movements. A nanomotor powered by visible light: sacrificial, kinetically assisted and intramolecular mechanisms.

 




PART 2: PHOTOCHEMICAL TECHNIQUES (Prof. Marco Montalti)

The course content can be split in two parts; introductive and theorethical the former, practical and based on the direct use of photochemical instrumentations and technics the latter. Firts part: 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). Second part: Spectroscopic characteritation of some compounds by practical determination of their absorption and emission spectra, emission lifetimes, photochemical reactivity, rection and emission quantum yields, actinometers. Moreover systems exhibiting sensitisation and quenching will be analized. Then practical experience of transient absorption spectroscopy will end thecourse.


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



Teaching methods

Prof. Paola Ceroni: the course consists of 6CFU 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. The laboratory experiences (2CFU) will be held by groups of max 3 students with the aim of reaching the manual ability and the necessary knowledge to perform a photochemical study.

Assessment methods

Oral examination for each of the two parts in which the course is divided (Prof. Ceroni and Prof. Montalti). The examination will verify that the student has acquired knowledge of photochemistry and the capacity to tackle real experimental problems related to photactive systems.

The final mark is calculated as the weighted average on the basis of the credit numbers of the two parts: Part 1, Prof. Ceroni (8 CFU) and Part 2, Prof. Montalti (4 CFU)

Teaching tools

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


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

Office hours

See the website of Paola Ceroni

See the website of Marco Montalti

SDGs

Affordable and clean energy

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