The fluorescence properties of riboflavin derivatives in various media have been studied by use of a sensitive apparatus that renders the direct measurement of corrected emission spectra in the wavelength range of 340–660mμ. The corrected emission (quantum) and excitation spectra of riboflavin tetrabutyrate in n-heptane have been recorded since it is slightly soluble in this hydrocarbon. The quantum spectrum shows clear peaks at 493 and 522mμ and a shoulder at 560 mμ, thus giving apparent mirror image to the three-banded longest wavelength band of the corrected excitation spectrum, which is expected to coincide with the absorption spectrum of this compound in n-heptane. General features of flavin fluorescence observed by changing the solvent from apolar to polar type are the red-shift of the emission maximum, the broadening of the peak, the disappearance of the threebanded structure, and the reduction of radiation probability. In particular, in the aqueous binary mixtures, the emission maximum and quantum yield of flavin fluorescence vary as a function of dielectric constant or of empirical Z-value that reflects the polarity of solvents. However, such linear correlation has not always been found when the effects of pure solvents of wide variety are tested. This fact suggests that the fluorescence properties of flavin are also considerably influenced by the solvent characteristics other than dielectric constants.
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Kotaki et al. (1970) studied this question.