High Mobility Solvent Holes in Methylcyclohexane

Using time-resolved dc photoconductivity, the migration patterns and reactions of solvent hole in liquid methylcyclohexane between 230 and 350 K have been studied. It is shown that solvent holes in liquid methylcyclohexane are reversibly scavenged by solutes whose liquid-state ionization potentials are 0.2−0.3 eV below that of the solvent. The reversible electron transfer is driven mainly by the reaction heat (60−90%); further decrease in the free energy is due to increase in entropy following the destruction of solvent structure around the hole. Between 133 and 360 K, the solvent hole diffuses with activation energy of 7.8 kJ/mol; the fastest electron-transfer reactions (ca. 8.7 × 10 10 M -1 s -1 at 25 °C) have activation energies between 3.9 and 5.3 kJ/mol (250 to 350 K). Unusually large scavenging radii, 1.5−3 nm, were obtained for these charge-transfer reactions.