New photochemically stable riboflavin analogue—3-Methyl-riboflavin tetraacetate

Spectroscopic and photophysical properties of a flavin analogue – 3-methyl-riboflavin tetraacetate – were studied in methanol, ethanol, water and acetonitrile. We compared experimental spectroscopic data with the results of theoretical predictions, obtained using the TD-DFT method. Based on these calculations, we assigned (π,π*) symmetry to both the lowest excited singlet and triplet states. We found the title compound to be a very efficient photosensitizer of singlet oxygen production (ϕΔ = 0.61). The triplet state quantum yield of 3-methyl-riboflavin tetraacetate was determined as 0.54 in methanolic solutions. Photodegradation quantum yield measurements demonstrate that the title compound may be used as a much more stable substitute of riboflavin, being two orders of magnitude more photostable (φR = 2 × 10−5). We also present exhaustive crystallographic characteristics of 3-methyl-riboflavin tetraacetate, along with time-resolved fluorescence spectra of its polycrystals.