Reversible ON/OFF and OFF/ON, light-stimulated binding, or release processes of metal cations from isatin diarylhydrazone complexes in solution

Abstract

In this paper, we studied the light-stimulated switching between states with a free metal cation and its bound form in a complex with diarylhydrazones I and II. Isatin diarylhydrazones with unique functionality have been prepared. The uniqueness of the functionality is because, with the help of hydrazone complexes, or hydrazones themselves in the presence of metals, it is possible to programmatically change (reversibly decrease or increase) the concentration of metals in a mixture of organic solvents and water or organic solvents by modulating light of different wavelengths. The E-isomers of the studied hydrazones are thermodynamically more stable than their Z-isomers. E-isomers form complexes with metals Mn+ (n = 1,2) e.g. Cu2+, Zn2+, Cd2+, Ni2+, Co2+, Fe2+, Sn2+, Hg2+, Pb2+. The E-isomers of the complexes do not thermally isomerize. After absorption of light (λ ≤ 405 nm), photochemical isomerization of the ligand occured, and the complex disappeared simultaneously. The product of this photochemical reaction was the Z-isomer of the ligand and the metal cation. By irradiating the reaction mixture thus formed with light (λ = 465 nm), a reversible photochemical reaction takes place, in which a complex with a ligand in the E configuration is formed. The Z-isomers do not form complexes with these metals.