Solvent influence on the electrochemical reduction of photochemically generated cis-azobenzene

cis-Azobenzene was generated from trans-azobenzene directly inside an electrochemical cell by irradiation with light from a mercury lamp. The formation of the cis-isomer was proved by recording the UV-VIS absorption spectra of a trans-azobenzene solution in acetonitrile after different periods of irradiation. The reduction half-wave potentials of cis-azobenzene have been determined by photomodulated voltammetry in eight solvents (acetonitrile, propionitrile, butyronitrile, benzonitrile, dimethylformamide, dimethylsulfoxide, propylene carbonate, and tetramethylurea), ranging from −1 to −2.2 V vs. SCE. A six step reaction mechanism is proposed. From the large variety of existing Linear Solvation Energy Relationships, the obtained half wave potentials fit well to the π*-scale and to the Unified Solvation Model.