Theoretical studies on the self-exchange electron-transfer reaction between 2,3-dicyano-5,6-dichloro- p-benzoquinone (DDQ) and its radical anion DDQ −[rad

Abstract

The structure of 2,3-dicyano-5,6-dichloro- p-benzoquinone (DDQ) and its radical anion was optimized by semi-empirical AM1, PM3, ab initio HF/3-21G, 6-31G, 6-31G(d), 6-31+G(d), and density functional B3LYP/6-31G(d), 6-31+G(d) methods. Nelsen’s model was used to calculate the internal reorganization energy λ i. The results of λ i from the AM1, PM3 and B3LYP methods are reasonable, while those from the HF method are too large because of not considering the effect of electron correlation. The linear reaction coordinate R was used to construct the double-well potential surface for the donor and acceptor, and then the transition state was determined at the point of R=0.50. Then Marcus’s two-sphere model was applied to estimate the solvent reorganization energy λ o in different solvents CH 3CN, benzonitrile, acetone, CHCl 3, and CH 2Cl 2. The electron transfer (ET) matrix element V rp was calculated using two-state model. The self-exchange ET reaction rate constants k ET in different solvents were calculated and the results were consistent with the experimental values. The reason why the behavior of self-exchange ET reaction between DDQ and DDQ − does not correlate with Marcus’s theory was discussed as well.