Solvent‐initiated photochemistry of transition metal complexes
Although it is generally assumed that photoreactions of transition metal complexes proceed through metal complex excited states, some reactions in halogenated solvents occur instead as radical processes, following carbon-halogen bond homolysis. Oxidation, substitution, or oxidative addition can occur by either a metal-centered or a solvent-initiated photoreaction, and they can be hard to distinguish. Under some circumstances even the kinetic rate laws can be the same. However, with proper choice of irradiation wavelength the dependence of the initial rate on light intensity and metal complex concentration suffices to discriminate between the two possibilities.
Patrick E. Hoggard, "Solvent‐initiated photochemistry of transition metal complexes", Coord. Chem. Rev. 159, 235‐243 (1997).