Abstract

The phenothiazine–phenylene–isoalloxazine dyad, 3-methyl-10-[4-(10-heptyl-10 H-phenothiazin-3-yl)-phenyl]-10 H-benzo[ g]pteridine-2,4-dione, dissolved in either dichloromethane or acetonitrile is characterized by absorption and emission spectroscopy. Absorption cross-section spectra, stimulated emission cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and degrees of fluorescence polarisation are determined. The fluorescence decay is determined by time-resolved measurements. The dye photo-stability is investigated by observation of absorption spectral changes due to prolonged blue-light excitation. The absorption spectrum of the dyad resembles the superposition of the absorption of the isoalloxazine (flavin) moiety and of the phenylphenothiazine moiety. Photo-excitation of the flavin moiety causes fluorescence quenching by ground-state reductive electron transfer from phenylphenothiazine to isoalloxazine followed by charge recombination. Photo-excitation of the phenothiazine moiety causes (i) efficient excited-state oxidative electron transfer from phenothiazine to isoalloxazine with successive recombination, and (ii) moderate energy transfer followed by ground-state phenothiazine electron transfer and recombination.

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