The effects of various trivalent lanthanide ions (acetates of Ce, Er, Eu, Nd) on the electronic absorption and fluorescence spectra of un-substituted coumarin-3-carboxylic acid (CCA) and 7-N,N-diethylamino-coumarin-3-carboxylic acid (DECCA) have been investigated in dimethylsulfoxide (DMSO) at room temperature. Depending on the lanthanide ion nature and concentration, significant spectral changes of absorption bands occurred for both coumarin derivatives. These spectral changes were attributed to the formation of ground-state complexes between the coumarin carboxylate derivatives and lanthanide ions. The fluorescence quenching of CCA and DECCA upon increasing the lanthanide ion concentration was studied. Different quantitative treatments, including the Stern-Volmer equation, the Perrin equation and a polynomial equation, were applied and compared in order to determine the nature of the quenching mechanisms for both coumarin derivatives. The results suggested the contribution of both dynamic and static quenching. Significant differences of CCA and DECCA fluorescence quenching efficiency were also observed, depending on the lanthanide ion. DECCA fluorescence lifetime measurements, performed in the absence and in the presence of Ln, confirmed a contribution of static quenching.

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Because of their important fluorescence properties, coumarins are widely applied in sensing devices. In this paper, the electronic inductive, mesomeric, and electromeric substituent effects on the electronic absorption and fluorescence spectra of 11 substituted coumarins, including NH 2 , NMe 2 , NEt 2 , OH, CF 3 , CH 3 , COOH, Cl, and Br substituents, have been quantitatively studied by means of structure-reactivity relationships. We have applied the Hammett, Brown-Okamoto, and Yukawa-Tsuno correlations to the coumarins electronic absorption and fluorescence spectra wavenumbers and Stokes shifts. The Stokes shift of coumarins decreased when the electron-donor inductive/ mesomeric power of the substituent increased. This Stokes shift decrease was more pronounced when the solvent polarity increased, which might be explained by the electromeric effect increase.

The mass spectrometry of a number of 6-substituted coumarins was studied in the context of correlating fragmentation pathways and electronic charges of atoms performed by AM1 semiempirical method. The atomic charges of atoms are found to be good predictors of the fragmentation pathways.