[摘要]：Spectral-fluorescent properties of 6-pyrazolyl-4-methylubbelliferone have been investigated in comparison with 4-methylumbelliferone and its methyl ester. Abnormally large Stokes shifts and the fluorescence ability of these compounds have been interpreted using quantum-chemical analysis by the DFT and TDDFT methods with the B3LYP/6-31G(d,p) basis set of the change of charge and bond orders in the ground and first excited states. It has been established that the significant difference in the absorption and fluorescence spectra of the studied 7-hydroxycoumarins in proton-donor solvents is caused by proton abstraction and transfer in their neutral form upon photoexcitation with probable formation of the anion and the tautomer depending the pH of the medium. It has been shown that the formation probability for these species is increased by introducing the pyrazolyl cycle in the 6-position of 4-methylumbelliferone.
