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Energy and Electron Transfer - II

Energy and Electron Transfer - II. Chapter-7 MMP+. P. H. December 19, 2002. Marcus Theory. - D G = l s + l v. Log k. normal. Inverted. - D G. Acc. Chem. Res., 1996, 29, 522. Example. k R >> k I. J. Am. Chem. Soc., 1989, 111, 8948. l = 0.39eV.

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Energy and Electron Transfer - II

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  1. Energy and Electron Transfer - II Chapter-7 MMP+ P. H. December 19, 2002

  2. Marcus Theory -DG = ls + lv Log k normal Inverted -DG Acc. Chem. Res., 1996, 29, 522

  3. Example kR >> kI J. Am. Chem. Soc., 1989, 111, 8948

  4. l = 0.39eV

  5. Contact and Solvent Separated Radical Ion Pairs CRIP SSRIP A D* D+ A-

  6. CRIP & SSRIP - An example DG2 = 1.8 kcal/mol k1 values depend on solvent polarity Dicloromethane -108 ; Hexane > 1010 Also more solvent reorganization for SSRIP than CRIP

  7. CRIP and Exciplexes - The Transition

  8. Electron and Energy Transfer Equilibria Can’t even happen without Energy transfer equilibrium

  9. Thermodynamics of the Equlibria For rigid systems For example.. DS - 0.04 gibbs/mol DS - -1.8 gibbs/mol

  10. Electron Transfer Equilibria Cannot observe the equlibrium if… kbet >> k–et

  11. Chemiluminescent Ion Recombination 1 2 Marcus Effect

  12. Role of Diffusion Diffusion and collision D*A becomes DA* DA* breaks up into D and A*

  13. Rate Constants: • kOBS, is close to calculated kDIFF. • kOBS is a function of T/. • kOBS is essentially invariant for quenchers of widely varying structure. • kOBS reach a limiting value which corresponds to the fastest bimolecular rate constant measured for that solvent. Obscured the Marcus Inverted Region

  14. Cage Effect

  15. Diffusion - Distance/Time Relationship Diffusion coefficient (D) of benzene (25°C) - 2 x 10–5 cm2/s; if we assume the encounter to be over when one of the molecules has traveled a distance equivalent to the size of several solvent molecules (e.g. x ~ 10 Å, equivalent to about 2 benzene molecules), then we obtain a rough estimate of the time required by applying above equation of about 2.5 x 10–10 s.

  16. Effect of Charged Species

  17. Transient Effects on Quenching With Incresing Time

  18. Static Quenching - Perrin Model ln ( ° / ) = V NA [ A] R (in Å) = 6.5 [A]1/3 (with [A] in M units)

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