Effect of the molecular structure of films of tetrapyrrole compounds on their photoelectrochemical characteristics for different types of sensitization

It was examined how the photoelectrochemical properties of thin films (50 nm) prepared from metal derivatives of tetrapyrrole compounds with various central atoms depend on the character of sensitization. It was demonstrated that the treatment of pigment films with oxygen and iodine vapor increases their photoactivity two- to threefold. A more pronounced effect is produced by deposition onto the films of layers of electron acceptors (o-chloranil, tetracyanoquinodimethane, etc.) or organic semiconductors (phenylselenodiimide) with a thickness of one to three monolayers. For tetrapyrrole compounds with the same structure of the macrocycle but with different central atoms, the sensitization effect may differ severalfold. For example, treatment of zinc tetraphenylporphyrin with iodine vapor increases the photocurrent by a factor of 14, with only a 1.5-fold increase being observed for cobalt tetraphenylporphyrin. The parameters of phthalocyanine metallocomplexes are less sensitive to sensitization compared to those of tetraphenylporphyrin metallocomplexes. The sequence of variation of the photoactivity of tetrapyrrole compounds according to the type of the central atom is not affected by the nature of the sensitizer, but the extent of change in the photoactivity is dependent on its properties, in particular, electron affinity.