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The absorption, excitation, and fluorescence spectra of the diterpenoid alkaloids, lappaeonitine and N-deacetyllappaconitine, in acetonitrile were studied. On the basis of the coincidence of the spectra with the analogous spectra of model compounds, methyl esters of anthranilic and N-acetylanthranilic acids, the conclusion was drawn that the --OOC(Ph}NRH groups are fluorochromes in the alkaloids studied. The high quantum yield of fluorescence and the bathofluoric shift in the luminescence and absorption spectra of N-deacetyllappaconitine were explained by an increase in the electron-releasing ability of the --NRH group in the deacetylation of lappaeonitine.

Fluorescence (FL) spectra were recorded and identified for the following 5-fluorouracil (FU) tautomers: 5fluoropyrimidine-2,4(1H,3H)-dione (A), 5-fluoro-2-hydroxypyrimidine-4(3H)-one (B), and 5-fluoro-4-hydroxypyrimidine-2(1H)-one (D), as well as the corresponding tautomers A and D of 1-(tetrahydrofuranyl-2)-5-fluorouracil and 1methyl-5-fluorouracil, tautomers A and B of 3-methyl-5fluorouracil, and the diketo tautomer of 1,3-dimethyl-5fluorouracil. It was shown that the FL of rare tautomers of FU derivatives occurs by the excitation of uracil homoassociates followed by intramolecular proton transfer (IPT), formation of a pair of rare tautomers, and radiative deactivation of one of them. The FL quantum yields φ i were estimated. In the case of rare tautomers, the φ i value includes the probability of IPT in the homoassociate, and density functional theory calculations in the TPSSTPSS/6-311+G(d,p) approximation were used to determine the relative energies of tautomers, associated FU forms, and their spectral properties that agree with the observed luminescence pattern.