Energy and Electron Transfer
MMP+ discussion Chapter 7 first half
December 17, 2002
Zhiqiang Liu
Transfer
Competing Processes upon encountering
Trivial Mechanism for energy transfer
Spectral Overlap Integral
Trivial Mechanism for electron transfer
http://chemed.chem.purdue.edu/demos/main_pages/9.4.html
Non-trivial energy transfer
Forster Theory of Coulombic Energy
Transfer
dipole-dipole interaction
2: orientation. Alignment factor
J: overlap. Energy match of donor and acceptor
R: distance between dipoles
Energy transfer by electron exchange
Dexter:
Comparison: Forster v. Dexter
Forster:
Dexter:
1.
2.
3.
4.
Dependence on separation. Dexter much stronger than Forster.
Forster depends on oscillator strength.
Both dependent on J.
Dexter involves excited states
Generating D and A*
Triplet Triplet Annihilation. Energy
transfer via electron exchange
Electron Transfer
Excited states: better oxidizing and reducing agents
Free energy for gas phase electron transfer
Free energy in solution phase
Gas phase results + terms for solution
G
Electrochemical potential in solution
Coulombic term in free energy of electron transfer
Libby vs. Marcus theory
Frank-Condon e Jump
Three events:
1. Electron transfer
2. Molecular reorientation
3. Solvent reorientation
Libby: Molecular and solvent after Electron.
Marcus:
Assumptions: 1. Loose bonding between molecules for classical phys/chem analysis
2. Geometrical and solvent reorientation to provide energy for the e jump
Libby vs. Marcus theory
Marcus for non zero free energy difference
Experimental evidence for Marcus Inverted Region