| Abstract
| - Electron-transfer reactions that are dissociative in nature can proceed via two mechanisms, stepwise andconcerted. In this work, the mechanism of photoinduced dissociative electron transfer between carbontetrachloride and four phenothiazine derivatives has been investigated by subpicosecond transient absorptionstudy. Clear evidence was obtained for the stepwise mechanism for the reaction between phenothiazine andcarbon tetrachloride, whereas for the other three derivatives concerted reaction is seen to be operative. Themechanism of the dissociative electron-transfer reaction has been correlated with the driving force of thereactions studied. A crossover of reaction mechanism from concerted to stepwise was observed with theincrease in the reducing power of the phenothiazine donor, i.e., with the increase in the driving force of thereaction. It was also shown that changes in solvent polarity can trigger the crossover of the reaction mechanism.The change in the reaction mechanism with the driving force of the reaction has been explained by potentialenergy surfaces involved in the two different mechanisms.
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