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Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
Photochemistry
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Photochemistry

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Transcript

  • 1. And God said, let there be light: and there was light.
  • 2. Milestones of Photochemistry/physics/biology
    • Primitive Earth Age: Small gas molecules + Sun light Nucleic acids and Proteins
    • 1805: Young’s double slit experiment (Wave nature of light)
    • 1864: Electromagnetic Wave theory of light (Maxwell)
    • 1886: First organic photochemical reaction by Giacomo Luigi Ciamician
    • 1887: Photoelectric effect (Heinrich Hertz)
    • Early 1900’s: Grotthus- Draper law
    • Early 1990s: Beer-Lambert law
    • 1900: Black body radiation: Quantum nature of light (Max Planck)
    • 1905: Quantum theory of radiation (Einstein).
    • 1909: Wave-particle duality (Einstein)
    • 1912: Stark-Einstein law
    • 1916: Concept of spontaneous absorption and emission (Einstein)
    • 1917: Concept of stimulated emission: Concept of MASER and LASER (Einstein)
    • 1918: Nobel prize: Max Planck: Energy quanta
    • 1921: Nobel Prize: Einstein: Photoelectric effect
    • 1926: Nomenclature of the light quantum as photon (Gilbert Lewis)
    • 1927: Nobel Prize: Arthur Compton: Compton effect: Photons carry momentum
    • 1953: Discovery of MASER: Charles H. Townes
    • 1960: Discovery of LASER: Theodore H. Maiman
    • 1967: Nobel prize: Manfred Eigen: Flash Photolysis to study ms-ns processes
    • 1971: Nobel prize: Gerhard Herzberg: Electronic structure of molecules
    • 1992: Nobel prize: Rudolf A. Marcus: Theory of electron transfer reactions
    • 1997: Nobel prize: Steven Chau: Laser cooling and trapping of atoms
    • 1999: Nobel prize: Ahmed H. Zewail: Femtosecond laser spectroscopy
    • 2000: Development of attosecond laser.
    • 2008: Nobel prize: Osamu Shimomura: Green fluorescent protein
    • 2009: Nobel prize: Charles K. Kao: Optical fibre cable
  • 3. Giacomo Luigi Ciamician: Father of Modern Molecular Photochemistry His first photochemistry experiment was published in 1886 and was titled “On the conversion of quinone into quinol by light”. Born August 25, 1857(1857-08-25) Trieste, Austria Died January 2, 1922 (aged 64) Bologna, Italy Education University of Vienna Employer University of Bologna
  • 4. Fundamental theories of Photochemistry
    • Grotthus-Draper law: Only that light which is absorbed by a system can cause chemical change.
    • Stark-Einstein law: One quantum of light is absorbed per molecule of absorbing and reacting substance that disappears.
    • Beer-Lambert law:
  • 5. Fundamental theories of Photochemistry
  • 6. Fundamental theories of Photochemistry
    • Selection rules:
      • Radiation transitions (Absorption, fluorescence)
      • Allowed transitions: g u, e.g.: S 0 S 1 and T 1 S 0
      • Forbidden transitions: g g, u u, e.g.: S 1 T 1
      • 2. Radiationless transitions (vibration relaxation, Internal conversion, Intersystem crossing)
      • Allowed transitions: g g, u u, e.g.: S 1 T 1
      • Forbidden transitions: g u, e.g.: S 0 S 1 and T 1 S 0
  • 7. Instrumentation
  • 8.  
  • 9.  
  • 10. Femtosecond Transient Absorption Spectroscopy
  • 11. Femtosecond Transient Absorption Spectroscopy
  • 12. Femtosecond Transient Absorption Spectroscopy
  • 13.  
  • 14. Femtosecond fluorescence upconversion setup
  • 15. Femtosecond Spectroscopy lab
  • 16. Absorption of Light by Ionic Compounds
    • Electrons can jump between “bands”
    • Incident light with energy ≥ than the “band gap” energy can be used to excite the electrons
  • 17. So What Does this Mean for Solar Cells?
    • In dye-sensitized solar cells…
      • Talk about highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
    • In single-crystal silicon solar cells…
      • Talk about “conduction band” (excited states) and “valence band” (ground states)
  • 18. A Closer Look at Solar Cells
    • How do traditional, silicon-based solar cells and newer, dye-sensitized solar cells work?
    • What are the advantages and disadvantages of each type of cell?
    Silicon-based solar cell Dye-sensitized solar cell
  • 19. How a Silicon-Based Solar Cell Works
    • A positive “hole” is left in the electron’s place
    • This separation of electrons and holes creates a voltage and a current
    • Light with energy greater than the band gap energy of Si is absorbed
    • Energy is given to an electron in the crystal lattice
    • The energy excites the electron; it is free to move
    Click image to launch animation (requires web access)
  • 20. How a Dye-Sensitized Cell Works Click image to launch animation (requires web access)
    • Light with high enough energy excites electrons in dye molecules
    • Excited electrons infused into semiconducting TiO 2 , transported out of cell
    • Positive “holes” left in dye molecules
    • Separation of excited electrons and “holes” creates a voltage
  • 21.  
  • 22. P=1.367kWm -2 - the solar constant – solar radiation power outside the Earth’s atmosphere Taken from: S. M. SZE; Physics of Semiconductor Devices; Second Edition; John Wiley & Sons;New York; 1981 SOLAR SPECTRAL IRRADIANCE
  • 23.  

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