THE EFFECT OF LIGHT ON THE THERMODYNAMIC-EQUILIBRIUM IN THE FORMATION OF THE COMPLEX BETWEEN VIOLOGEN AND THE FERROCYANIDE ION

The formation of the complex between N,N'-dibutyl-4,4'-dipyridilium dibromide and potassium ferrocyanide was studied in aqueous solutions. The charge transfer band was observed and the composition of the complex between the dipyridilium dication and the ferrocyanide ion (1 : 1) was established. The irradiation (lambda less than or equal to 350 nm) of deaerated solutions in the absorption region of individual components results in a shift of the thermodynamic equilibrium towards complex formation via the intermediate formation of an exciplex. Since the absorption maximum of the complex is located in the visible region (lambda = 528 nm), its reversible formation and decomposition are accompanied by reversible coloring of the solution, i.e., the system is photochromic.