Abdoulaye Djandé

Revisiting the photophysical properties and excited singlet-state dipole moments of several coumarin derivatives

The solvent effects on the electronic absorption and fluorescence emission spectra of several coumarins derivatives, containing amino, N,N-dimethyl-amino, N,N-diethyl-amino, hydroxyl, methyl, carboxyl, or halogen substituents at the positions 7, 4, or 3, were investigated in eight solvents with various polarities. The first excited singlet-state dipole moments of these coumarins were determined by various solvatochromic methods, using the theoretical ground-state dipole moments which were calculated by the AM1 method. The first excited singlet-state dipole moment values were obtained by the Bakhshiev, Kawski-Chamma-Viallet, Lippert-Mataga, and Reichardt-Dimroth equations, and were compared to the ground-state dipole moments. In all cases, the dipole moments were found to be higher in the excited singlet-state than in the ground state because of the different electron densities in both states. The red-shifts of the absorption and fluorescence emission bands, observed for most compounds upon increasing the solvent polarity, indicated that the electronic transitions were of π-π* nature.

2-Oxo-2H-chromen-4-yl 4-methyl­benzoate

The asymmetric unit of the title compound, C17H12O4, consists of two independent molecules. The chromen-2-one ring and the 4-methylbenzoate side chain are inclined to one another at a dihedral angle of 64.79 (10)° in one molecule and 88.3 (1)° in the other. In the crystal, molecules form R 2 2(8) centrosymmetric dimers via C—H⋯O hydrogen bonds. These dimers are stacked by C—H⋯O hydrogen bonds, resulting in R 2 2(18) and R 3 2(16) ring motifs. π–π stacking interactions between two parallel chromen-2-one rings, with centroid–centroid distances of 3.743 (1) and 3.771 (1) Å, are also present.

Crystal structure of 2-oxo-2H-chromen-3-yl propano­ate

In the title compound, C12H9O4, the dihedral angle between the coumarin ring system and the propionate side chain is 78.48 (8)°.

Crystal structure of 2-oxo-2H-chromen-3-yl 4-chloro­benzoate and Hirshfeld surface analysis

In the title compound, C16H9ClO4, the dihedral angle between the coumarin ring system [maximum deviation = 0.023 (1) Å] and the benzene ring is 73.95 (8)°.

2-Oxo-2H-chromen-4-yl 4-tert-butyl-benzoate.

In the title molecule, C20H18O4, the three methyl groups of the tert-butyl substituent show rotational disorder. Each methyl group is split over three positions, with refined site-occupation factors of 0.711 (4), 0.146 (3) and 0.144 (4). The benzene ring of the benzoate group is oriented at a dihedral angle of 60.70 (7)° with respect to the planar chromene ring [maximum deviation = 0.046 (2) Å]. The crystal structure features centrosymmetric R 2 2(8) dimers formed via C—H⋯O interactions, and these dimeric aggregates are connected by C—H⋯π interactions.

2-Oxochromen-4-yl 4-(dimethyl­amino)­benzoate

In the title molecule, C18H15NO4, the benzoate ring is oriented at a dihedral angle of 43.43 (6)° with respect to the planar [maximum deviation = 0.038 (2) Å] chromene ring. The crystal structure features R 2 2(12) centrosymetric dimers formed via C—H⋯O interactions and these dimeric aggregates are connected by C—H⋯π interactions.

2-Oxo-2H-chromen-4-yl propionate

In the title compound, C12H10O4, the atoms of the 2-oxo-2H-chromene ring system and the non-H atoms of the 4-substituent all lie on a crystallographic mirror plane. The molecular structure exhibits an intramolecular C—H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, molecules form R 3 2(12) trimeric units via C—H⋯O interactions which propagate into layers parallel to the ac plane. These layers are linked by weak C—H⋯O interactions along the [010] direction, generating a three-dimensional network.

2-Oxo-2H-chromen-7-yl 4-tert-butyl­benzoate

The structure of a coumarin ester is reported and compared with the results of a quantum chemical calculation. In the crystal, intermolecular C—H⋯O contacts generate an infinite C(6) chain along the b axis. C=O⋯π and π–π stacking interactions also occur. Hirshfeld surface analysis was used to confirm and quantify the supramolecular interactions.

Crystal structure of 2-oxo-2H-chromen-7-yl 4-fluoro­benzoate

The structure of a coumarin ester stabilized by C—H⋯O hydrogen bonds and C=O⋯π and π–π stacking interactions has been studied by X-ray diffraction, Hirshfeld surface analysis and quantum chemical calculations.

Fluorescence Quenching of Two Coumarin-3-carboxylic Acids by Trivalent Lanthanide Ions

The effects of various trivalent lanthanide ions (acetates of Ce3+, Er3+, Eu3+, Nd3+) 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 Ln3+, confirmed a contribution of static quenching.