PHOTOREDOX PROPERTIES OF KOJIC ACID AND ITS DERIVATIVES COMPLEXED TO IRON(III)

Iron(III) complexes of the form cis-[Fe(SB)(X-K)] in which SB2- are op en-chain tetradentate Schiff base N2O2-ligands of acacen, benacen or s alen type, and X-K- are bidentate anions of kojic acid (5-hydroxy-2-hy droxymethyl-4H-pyran-4-one) or other gamma-pyranones undergo photoredo x transformations when being irradiated in methanol into intraligand o r LMCT bands. The quantum yields of the photoredox reactions depend on the peripheral constitution of the N2O2 ligands, the substituents A a nd B of the ligands X-K-, and the wavelength of irradiation lambda(irr ). The proposed mechanism involves the population of photoredox reacti ve LMCT states by photophysical deactivation steps, primary photoredox formation of X-K-. radicals and Fe(II), and subsequent ''dark'' redox processes giving back the anions X-K- and the final products Fe(II) a nd formaldehyde formed in the molar ratio 2:1.