Electrochemical behavior of conjugated quinoxaline derivatives

The electrochemical behavior of three kinds of conjugated quinoxaline derivatives has been studied in 95% DMF + water mixed acidic media. These compounds are electrochemically reduced by one, two or three steps which are equal to the number of pyrazine rings in the individual molecules. Using cyclic voltammetry, hydrodynamic chronocoulometry and rotating disk voltammetry, it was found that each reduction step is a two-electron/two-proton process. The formation energies of the possible reduction intermediates were calculated using the MOPAC PM3 method, showing that the pyrazine rings act as the redox centers of the individual molecules and are reduced ring by ring as two-electron/two-proton processes. The observed electrochemical behavior, which is similar to that of conjugated polynuclear metal complexes, could also be explained theoretically by the so-called additive pair model. Both the experimental and theoretical data show that, with the increase in the number of pyrazine rings in the molecule, it becomes more easily reduced, which is due to the conjugation interaction between the redox centers in the molecule. It is also demonstrated that the conjugation interaction energies between the nearby pair of redox centers are different in different redox states.