SOLVENT GATING OF INTRAMOLECULAR ELECTRON-TRANSFER

Citation
Rm. Miller et al., SOLVENT GATING OF INTRAMOLECULAR ELECTRON-TRANSFER, Journal of physical chemistry, 98(5), 1994, pp. 1376-1385
Citations number
61
Categorie Soggetti
Chemistry Physical
ISSN journal
00223654
Volume
98
Issue
5
Year of publication
1994
Pages
1376 - 1385
Database
ISI
SICI code
0022-3654(1994)98:5<1376:SGOIE>2.0.ZU;2-Z
Abstract
The rates for ionic photodissociation of malachite green leucocyanide to form cyanide ion and a malachite green carbonium ion were measured as a function of solvent and temperature. The observed rates in mixtur es of polar and nonpolar solvents all had an activation energy of abou t 2 kcal/mol for a wide range of dielectric constants. This dissociati ve intramolecular electron transfer (DIET) is unusual because it is th e first example where solvent configurational entropy changes are requ ired to enable a large amplitude molecular distortion leading to a non adiabatic electron transfer and ionic dissociation. This solvent gated intramolecular electron-transfer mechanism is supported by analysis o f the preexponential and activation energy trends in dipolar aprotic s olvent mixtures and alcohol solvents. The large amplitude motion is no t separately measurable due to the slow gating rates, but viscosity ef fects on both the preexponential and the activation energy are analyze d to demonstrate consistency with a barrierless diffusion model having a structural dependence on electron-transfer rate. The rate has an in verse dependence on viscosity raised to the 0.53 power.