Photochemical conversion and storage of solar energy by azobenzene.

Abstract

Photochemical isomerization of trans-azobenzene to cis-isomer, and its inverse cis-trans isomerization were investigated for the purpose of constructing a thermal energy storage system by conversion of solar light energy. Trans-cis photoisomerization of azobenzene in the cyclohexane solution proceeded with or without photosensitizers over a wide range of light in the ultraviolet and visible region. But the backward reaction from cis- to trans-form, which was predominant by the longer-wavelength light, set a limit to the progress of trans-cis conversion, and photochemical equilibrium was established at about 25% conversion of trans-azobenzene. Some devices to remove the conversion limit were examined. Cis-trans isomerization in the dark was carried out in the presence of immobilized metal porphine catalyst. Cotetraphenylporphine or Co-protoporphyrin fixed on polyethylene granules graft-polymerized with chloromethylstyrene was the most effective for the reverse reaction. This liberation of heat during the reaction was also analyzed from the kinetic point of view.