Substituent Effects and Correlations of Electrochemical Behaviors with Molecular Orbital Calculation of Thioxantone Derivatives￥°

摘要

This paper presents the electrochemistry and molecular orbital (MO) picture of a series of conformationally-restricted thioxantone derivatives. A series of C2-substituted thioxanthones were examined to probe the electronic influence of the substituent on the electrooxidation and electroreduction sites (i.e., on the electron densities at the 10-and 9-positions), respectively. In the presence of "electrophoric" groups such as C=O and S, characteristic electrochemical reduction and oxidation responses are observed. The electrochemical reaction was diffusion-controlled, because the ip/ヴ1/2 ratio was constant for the anodic and cathodic wave of thioxantone derivatives. These substituent effects are presented in terms of correlations of oxidation (or reduction) potentials with the highest occupied molecular orbital (HOMO), or lowest unoccupied molecular orbital (LUMO) energies, respectively. There is good correlation between energies of the HOMO vs. Epa(+) and energies of the LUMO vs. Epc(-). Frontier Molecular Orbital (FMO) is changed by the functional group of thioxanthones. FMO energy level was offered us the information about the electron transfer direction, and the coefficient of FMO was offered the information about the electron transfer position. Sulfur atom has an important effect on oxidation potential, Epa(+) and the carbonyl carbon has an important effect on reduction potential, Epc(-). Therefore we were appreciated that the contribution of sulfur atom for the Epa(+) and HOMO energies is larger than the contribution of carbonyl group for the Epc(-) and LUMO energies.