Jean Bourson

Ion-responsive fluorescent compounds: Part 3. Cation complexation with coumarin 153 linked to monoaza-15-crown-5

Abstract The complexation ability of coumarin 153 linked to monoaza-15-crown-5 was studied. On complexation by alkaline earth metal ions and aluminium ion, both absorption and emission spectra undergo a marked red shift whereas the effects are weaker with alkali metal ions. Owing to the participation of the carbonyl group of the coumarin, the stability of the complexes is much higher than those observed with previously described fluorophores linked to monoaza-15-crown-5. The stability of the complexes remains high enough in acetonitrile—water mixtures for practical application to the determination of cation concentrations in aqueous samples to be possible

Photoejection of cations from complexes with a crown-ether-linked merocyanine evidenced by ultrafast spectroscopy

Direct evidence of photoejection of lithium and calcium ions from a crown-ether-linked merocyanine is provided by picosecond pump—probe supercontinuum spectroscopy. The photoejection process takes place in less than 5 and 20 ps for the Li+ and Ca2+ complexes, respectively. The stability constants of the complexes in the excited state are estimated to be two orders of magnitude lower than in the ground state.

Efficiency of intramolecular electronic energy transfer in coumarin bichromophoric molecules

Intramolecular energy transfer in bichromorhoric molecules consisting of two coumarins linked by a variable number of methylene groups (n = 3, 4, 8, 12), was studied with special attention to the effects of n, temperature, viscosity and solvent nature on the efficiency of transfer. The validity of model compounds for the donor and acceptor moieties was carefully examined. Fluorescence polarization experiments revealed that a non-randomicity of mutual orientation of donor and acceptor can only be small, if any. Dual fluorescence from donor and acceptor was observed in propylene glycol whatever the value of n and at any temperature ranging from -60 to 60°C. Fluorescence from the donor was not detectable in dimethylformamide owing to the very low quantum yield of the donor in this solvent. Transfer efficiencies were determined by three steady-state methods and were found to be more dependent on n in dimethylformamide than in propylene glycol. Incomplete energy transfer is clearly shown in the case of dimethylformamide as a solvent. The effects of temperature are weak in the -60, + 60°C range. The results are discussed in light of theories of energy transfer.

Coumarinic Fluorescent Chemosensors for the Detection of Transition Metal Ions

Fluoroionophores consisting of coumarin-153 linked to mono- and diaza-crown ethers are able to complex transition metal cations (Ni2+, Zn2+, Cd2+) and Pb2+, with concomitant large changes in photophysical properties. The stability constants in acetonitrile are higher than 3×106M−1 except for Ni2+.

Frequency conversion of light by intramolecular energy transfer in bifluorophoric molecules

Abstract A new type of bifluorophoric molecule consisting of two coumarins linked by a short saturated chain is studied. The energy transfer efficiency is close to I and a good photochemical stability is expected. Therefore, this type of compound is well suited for efficient frequency conversion of light and can thus be used in various applications such as scintillators or fluorescent solar concentrators.

Spectral properties of a new flourescent dye emitting in the red: A benzoxazinone derivative

Abstract 7-dimethylamino-3( p -formylstyryl)-1,4-benzoxazine-2-one (DFSBO) is a new dye emitting in the red which may be useful for several applications owing to its interesting spectral properties: a board first absorption band, large Stokes shift, and good quantum yield with a very small temperature and excitation-wavelenghth dependence.

Chromoionophores derived from a coumarin linked to monoaza-and diaza-crown ethers: Formation of divalent 3d metal complexes

Abstract The complexing properties of a series of Chromoionophores consisting of a C-153 coumarin linked to an aza- or diaza-crown ether are studied in acetonitrile and methanol by UV spectrometry. Cations under study are copper, nickel, zinc, cadmium and lead. The high stability constants of the complexes arise from the participation of the carbonyl group of the coumarin into the complexes and from the deconjugation of the nitrogen atom of the aza-crown ether from the π-electron system. A comparison made with previous results obtained for alkaline-earth cations shows that the new complexes present in most cases more shifted characteristic absorption wavelengths.

A new concept of photogeneration of cations: Evidence for photoejection of Ca2+ and Li+ from complexes with a crown-ether-linked merocyanine by picosecond spectroscopy

Time-resolved transient absorption and gain spectra of DCM-crown and its complexes with Li+ and Ca2+ in acetonitrile are measured in the wavelength range 370–670 nm after subpicosecond excitation at 425 nm. The results give evidence for the fast formation of free DCM-crown from both excited complexes, with a faster rate for the Li+ complex. A two-step mechanism is found for the initial decay (within 30 ps) of the free DCM-crown.

Asymmetric hydrogenations catalysed by diphosphinite rhodium complexes derived from natural tartaric acid

Abstract Two chiral diphosphinites, derived from natural tartaric acid, have been prepared and used as ligands for the preparation of two asymmetric hydrogenation catalysts, which were isolated in a crystalline state. After several weeks storage, these catlysts are still effective in the asymmetric hydrogenation of α-acetamido- and α-benzamido-cinnamic acid, citraconic acid, 2-phenyl-1-butene. In the hydrogenation of amino acid precursors the optical yields ranged from 14 to 44%. Starting from a given substrate, each of the two enantiomers can be obtained by appropriate choice of one of our two catalysts, which are thus complementary to each other. The influence on the optical yield of various factors in the hydrogenations are considered.

Voltage-Controlled Fluorometry of the Transfer of Nonfluorescent Ions across the 1,2-Dichloroethane/Water Interface Using Fluorescent Ionophores.

The voltage-driven transfer of alkali and alkaline-earth metal ions across the polarized 1,2-dichloroethane (DCE)/water interface has been measured fluorometrically by using two fluorescent ionophores, coumarin 153-linked monoaza-15-crown-5 (C153-crown(O(4))) and two-coumarin 153-linked diaza-18-crown-6 ((C153)(2)-K(22)). The 1:1 complex formation prevails for both monovalent and divalent ion transfer, when the concentration of C153-crown(O(4)) in DCE is at the micromolar level. In the Mg(2+) ion transfer, the formation of the 1:2 (metal-ligand) complex becomes significant at the millimolar level of C153-crown(O(4)). C153-crown(O(4)) seems to adsorb at the interface. The complexation of Ba(2+) with (C153)(2)-K(22) is significantly slower than the complexation with C153-crown(O(4)).