PHOTOCHEMICAL HYDROXYLATION OF 7,8‐DIMETHYLALLOXAZINE (LUMICHROME)‐A FLASH PHOTOLYSIS STUDY

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Abstract
Abstract—Flash photolysis experiments on the hydroxylation of lumichrome (L) in aqueous 0.5 M H2SO4solution in the presence of O2or Ni2+as triplet quenchers and quantum yield measurements confirm the assignment of the photoreactive species to the protonated form of the excited singlet state. A mechamism concerning the photochemical step is proposed, accounting for the formation of protonated 9‐hydroxy‐5,10‐dihydrolumichrome (LOH3+). This primary stable photoproduct was characterized by spectral and kinetic data. The dark reactions originating from LOH3+were investigated, and data regarding the successive steps are presented. The reaction LOH3+L→ LO + LH3+is demonstrated to be a two‐electron reduction. The rate constant for the reaction of LH2+with O2is much larger than that for the oxidation of LH3+by oxygen.