Dynamic Solvent Effects on Electron Transfer Rates in the Inverted Regime: Ultrafast Studies on the Betaines
MINNESOTA UNIV MINNEAPOLIS DEPT OF CHEMISTRY
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Transient pump-probe measurements have been made on Betaine-30, the solvent polarity probe. Betaine-30 is composed of organic donor and acceptor groups. The transient data has been analyzed to measure k sub et the electron transfer et rate constant, in polar solvents for this inverted regime et. The observed rate constant, in various polar solvents is as much as a factor of 100, 000 larger than is predicted by the standard, classical, implementation of the theory of Sumi and Marcus, using Kjaer and Ulstrups estimates for necessary parameters. In contrast, a quantum treatment of the vibrational modes by Jortner and Bixon, which includes the dynamic solvent effect, predicts that the rate should be approximately k sub et, JB1 tau sub s. This is close to the experimental results in typical polar aprotic solvents. The kinetic behavior of Betaine-30 in slowly relaxing solvents is shown to be in the diffusionless limit of the hybrid, generalized Sumi-MarcusJortner-Bixon picture.
- Organic Chemistry
- Physical Chemistry
- Radiation and Nuclear Chemistry