Experiments and theoretical calculations by density functional theory (DFT) have been carried out to examine a self-sensitized type I photooxidation of toluidine blue O (TBO+). This study attempts to build a connection between visible-light photolysis and demethylation processes of methylamine compounds, such as TBO+. We show that controlled photoinduced mono- and double-demethylation of TBO+ can be achieved. The kinetics for the appearance rate of the mono-demethylated TBO+ and the double-demethylated TBO+ were found to fit pseudo-first-order kinetics. DFT calculations have been used to examine the demethylation of TBO+ and included N,N-dimethylaniline as a model compound for TBO+. The results show an oxygen-dependent demethylation process. The mechanism for the sequential methyl loss is proposed to be due to H • or e–/H+ transfer to 3TBO+* followed by a reaction of TBO+• with O2, yielding a C-peroxyTBO+• intermediate. Instead of aminyl radical peroxyl formation, i.e., N-peroxyTBO+• , the C-centered peroxyTBO+• is favored, that upon dimerization (Russell mechanism) leads to dissociation of formaldehyde from the methylamine site.

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Relevant antioxidant properties of non-phenolic 7-dialkyl-aminocoumarins against free radicals derived from 2,2′-azobis(2-amidinopropane) dihydrochloride under aerobic conditions have been experimentally and theoretically demonstrated.