Light-induced multistep redox reactions: The diode-array spectrophotometer as a photoreactor

The light source of a photometer may induce chemical reactions in photosensitive reactive systems. Diode-array spectrophotometers are particularly suitable for producing such phenomena. This paper provides an overview on how this equipment can be used as a photoreactor. The principles of various techniques to control the intensity and spectral region of the illuminating light are discussed in detail. It will be shown that the quantum yields of various photochemically induced redox reactions can be determined by exploiting specific features of diode-array spectrophotometers. Kinetic coupling between primary photo-chemical and secondary thermally activated reaction steps are utilized to explore intimate details of composite redox reactions. Key aspects of the method applied are demonstrated via the photoreactions of 2,6-dichloro-1,4-benzoquinone (DCQ), the photoinduced autoxidation of S(IV) and a photochemically activated redox reaction of the chlorate ion.