Reversible transformation between the oxidized and reduced forms of redox coenzyme analogues

Reversible transformation between 10-methylacridinium ion (AcrH ⁺) and 9,10-dihydro-10-methylacridine (AcrH₂) has been achieved by combining the photo-reduction of AcrH⁺ by benzyl alcohol derivatives in MeCN at 298 K under irradiation of visible light of λ > 360 nm with the thermal oxidation of AcrH₂ by the corresponding benzaldehyde derivatives at 333 K. The photo-reduction of AcrH⁺ by a benzyl alcohol derivative can also be combined with the photo-oxidation of AcrH₂ by dibenzyl disulphide under irradiation of light of λ 285 nm which corresponds to the absorption maximum of AcrH₂. Under continuous irradiation of light from a Xenon lamp, the AcrH⁺/ AcrH₂ redox pair acts as a photocatalyst for the oxidation of p-chlorobenzyl alcohol by dibenzyl disulphide to yield p-chlorobenzaldehyde and toluene-α-thiol. Reversible transformation between riboflavin-2′, 3′,4′,5′-tetra-acetate (Fl) and the corresponding 1,5-dihydroflavin (FlH₂) has also been achieved by utilizing all possible combinations of thermal and photochemical reactions in controlling the direction of the redox reaction between Fl and benzenethiol derivatives, i.e., the forward thermal reduction of Fl by benzenethiol derivatives combined with the reverse photo-oxidation of FlH₂ by the corresponding disulphides, the forward photo-reduction of Fl and the reverse photo-oxidation of FlH ₂ under irradiation with light of different wavelengths, and the forward photo-reduction of Fl combined with the reverse thermal oxidation of FlH₂.