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. Dependence on separation. Dexter much stronger than Forster.

2. Forster depends on oscillator strength.

3. Both dependent on J.

4. 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

 G Free energy in solution phase Gas phase results + terms for solution 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