The use of semiconductor electrodes in the study of photochemical reactions

Semiconductor electrodes can act either as donors or acceptors for electron exchange with excited molecules in the electrolyte. Unlike at metal surfaces, reaction with both the ground level and the excited level will not occur simultaneously provided that the semiconductor has a sufficiently large band gap. It is therefore possible to observe the injection of electrons or of holes into the semiconductor. The photocurrents produced in this way can be used to investigate the photochemical behaviour of the excited molecule. A series of examples is given in which the injected photocurrents are increased or decreased by simultaneously occurring reactions between the excited molecules and other species in the electrolyte. The interpretation of the observed effects is compatible with the notions concerning analogous homogeneous photochemical reactions.