Dinkars presentation on potochemistry.
4 likes3,607 views
This document summarizes a seminar on photochemistry presented by Mr. Dinkar B. Kamkhede. The seminar covered topics including the definition of photochemistry, laws of photochemistry, mechanisms of light absorption, electronic transitions, photosensitization, and the Jablonski diagram. It discussed how photochemical reactions are initiated by the absorption of light energy and explained concepts such as quantum yield. The seminar provided an overview of the key concepts and processes in photochemistry.
![Energy transfer through photosensitization
D 1D
h
1D 3D
ISC
A + 3D D + 3A
3A Products
D = Donor
A = Acceptor
1 = Singlet
3 = Triplet
S0
S1
74 Kcal
.mole-1 69 Kcal/mole
T1
ISC
120 Kcal/mole
S0
T1
S1
60 Kcal/mole
Energy transfer
Benzophenone Butadiene
Ph2CO
h
1[Ph2CO]
ISC 3[Ph2CO]
+ Ph2CO
3
Dimeric products](https://image.slidesharecdn.com/dinkarpotochemistryppt-150310035758-conversion-gate01/85/Dinkars-presentation-on-potochemistry-11-320.jpg)
Dinkars presentation on potochemistry.
- 1. SEMINAR ON PHOTOCHEMISTRY Presented By:- Mr.Dinkar B.Kamkhede MSc.Chemistry,IIYear 2013-2014 Vidyabharati Mahavidyalay, Amravati.
- 2. Introduction Photochemistry is concerned with the changes in chemical and physical behaviour of molecules following absorption of one or (more) photons. Primarily consider absorption of visible/UV although IR absorption may also change chemical behaviour Mainly concerned with electronic excitation, usually accompanied by some vibrational excitation And (rotational in gas phase ) excitation. Contents- Introduction Phoyochemistry Intracion of Radition with matter Electronic Transition Laws of Photochemistry Mechanisim of Light Absorption Photosensitisation Joblonski Digram Modes of Dissipation of Energy Energy Transfer
- 3. Photochemistry Chemical reactions- 1 .Thermal Reaction-The Reaction proceed with the absorption of heat energy. Action of light → chemical change (light induced reactions) 2 .Photochemical Reaction-The Reaction takes place by the absorsption of light energy. The Chemical reaction that are initiated or affected by Light called photochemical reaction. Chemical reaction → light emission (chemiluminescence)
- 4. Intraction of Radiations with Matter Light: electromagnetic field vibration spreading in quanta (photons) Photon: the smallest amount of light carrying energy Quantise- transition means for a particular energy molecule absorbed specific amount of energy.which lead to chemical change in a molecule due to absorption of EMR. Energy of photons (A. Einstein)- E = c h h= h = Planck’s constant (6.6 · 10-34 Js) c = speed of light (3 · 108 ms-1) l = wavelength n = frequency Einstein’s Equivalency Principle- One particle of a chemical substance can absorb only one photon from a light beam: DE = h
- 5. Types of Excitation Organic Compound σ → σ* Alkane,Which has only 6 -bon n → σ* Alcohol,Amine,Ether, Thioether,etc π → π* Alkene compound,etc n → π* Corbonyl Compound,etc Electronic Transition`s
- 6. Photochemical Process given two Laws of Photochemistry 1. (Grotthus, Draper) - 1st Law of Photochemistry 2. (Stark, Einstein) - 2nd Law of Photochemistry 3. Q uantum yield or Quantum Efficiency 4. if Law is correct then quantum yield should be unitly.This law ever is very rare. - number of molecules undergoing the process number of quanta absorbed=
- 7. Mechanisms of Light Absorption Excitation: X2 h *X2 A bonding electron is lifted to a higher energy level (higher orbital) INTERACTION OF LIGHT AND MATERIALS: a) X2* → X2 + M* (excess energy transferred to the surrounding) b) X2* → X2 + hn (fluorescence or phosphorescence) c) X2* + Y → chemical reaction (excess energy supplies the activation energy of the reaction)
- 8. When any transition attain Triplet state it return back to GS , i.s Energy gap between T1-So is constant.f or a perticular type of transition. during Phosphorasence emitted in energy may be absorbed by other molecule o produce its own curresponding T.S. called Photosensitization Photosensitization
- 9. Jablonski Diagram It explain discription of molecule present in different Energy level after absorption of EMR.
- 10. Modes of Dissipation of Energy (S0) (S1) 10-8s (S2) 10-11s (T1) 10-3s-1s S2 : The higher vibrational level of the excited singlet state S1 IC: Internal conversion; RD: Radiative deactivation F: Fluorescence (spin consevation); ISC: Inter system crossing P: Phosphorescence (Spin inversion). h IC RD F ISC P RD (Jablonski diagram) Deactivation no radiative IC ISC (Spin inversion) radiative F P S1 T1 + + + photosensitization
- 11. Energy transfer through photosensitization D 1D h 1D 3D ISC A + 3D D + 3A 3A Products D = Donor A = Acceptor 1 = Singlet 3 = Triplet S0 S1 74 Kcal .mole-1 69 Kcal/mole T1 ISC 120 Kcal/mole S0 T1 S1 60 Kcal/mole Energy transfer Benzophenone Butadiene Ph2CO h 1[Ph2CO] ISC 3[Ph2CO] + Ph2CO 3 Dimeric products
- 13. Criteria of an ideal sensitizer • It must be excited by the irradiation to be used, small singlet triplet splitting. High ISC yield. • It must be present in sufficient concentration to absorb more strongly than the other reactants under the condition. • It must be able to transfer energy to the desired reactant, low chemical reactivity in Triplet state. Internal conversion • Internal conversion nearly always involves change of orbital configuration. • Nuclear kinetic energy operator is totally symmetric, suggesting IC is formally forbidden. • However separation of Franck Condon factor not strictly valid because Hamiltonian depends on nuclear co-ordinates.