The reductive quenching results in reduction of Fe(III) in the excited complex accompanied by oxidation of EDTA and/or external electron acceptor; thus the process can be identified as photoreduction of the Fe(III) complex.
Numerical analysis of the [Fe(edta)(H2O]− and [Fe(edta)(OH)]2− absorption spectra leads to conclusion that there are two different LMCT excited states, which differ in location of the unpaired electron (on N or O atom). Reactive decay of these excited states leads, however, to generation of analogous products, although with different quantum yields.
The Fe(III) photocatalytic cycle can be driven by sunlight and in the aerated media plays a crucial role in abatement of the pollutants, which have either electron donor or electron acceptor character. Among others, the photocatalytic cycle contributes to abate one of the most noxious pollutants, i.e. chromate(VI).