Bernard Valeur

A mesoporous silica functionalized by a covalently bound calixarene-based fluoroionophore for selective optical sensing of mercury(II) in water

With the aim of optical sensing of Hg2+ in water, a calixarene bearing two dansyl fluorophores was grafted on a large pore mesoporous silica material (SBA-15) via two long alkyl chains containing triethoxysilane groups. The characterization of the obtained material 2-SBA-15 shows that the organized structure is preserved after the post-grafting procedure. A detailed study of the complexing and fluorescence properties of 2-SBA-15 is reported. The functionalized material is able to reversibly detect Hg2+ with a response time of a few seconds and a detection limit of 3.3 × 10−7 mol L−1 in water. Furthermore, this system offers a high selectivity over several interfering cations (Na+, K+, Ca2+, Cu2+, Cd2+, Pb2+).

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

A highly selective fluorescent molecular sensor for potassium based on a calix[4]bisazacrown bearing boron-dipyrromethene fluorophores

The synthesis of a ditopic fluorescent sensor for cations associating a 1,3 alternate calix[4]bisazacrown-5 as an ionophore and substituted boron-dipyrromethene dyes as fluorophores is reported. Photophysical studies revealed that in medium and high polarity solvents an efficient charge transfer (CT) reaction occurs in the excited state leading to a dual emission and a strong quenching of fluorescence. This CT process is either totally suppressed by amino group protonation or hampered by cation complexation; in both cases, a strong fluorescence enhancement is observed. This “switching-on” of the emission is more pronounced when two cations are coordinated. The stability constants of complexes with sodium, potassium, caesium, calcium and barium cations were measured in acetonitrile and ethanol. The system shows a high sensitivity and selectivity for potassium over other metal ions. A test under physiological conditions was successfully achieved.

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.

Pitfalls and their remedies in time-resolved fluorescence spectroscopy and microscopy.

Time-resolved fluorescence spectroscopy and microscopy in both time and frequency domains provide very useful and accurate information on dynamic processes. Good quality data are essential in obtaining reliable parameter estimates. Distortions of the fluorescence response due to artifacts may have disastrous consequences. We provide here a concise overview of potential difficulties encountered under daily laboratory circumstances in the use of time- and frequency-domain equipment as well as practical remedies against common error conditions, elucidated with several graphs to aid the researcher in visual inspection and quality-control of collected data. A range of artifacts due to sample preparation or to optical and electronic pitfalls are discussed, as are remedies against them. Also recommended data analysis strategies are described.

Ion-responsive fluorescent compounds V. Photophysical and complexing properties of coumarin 343 linked to monoaza-15-crown-5

The photophysical and complexing properties of a fluoroionophore consisting of coumarin 343 linked to monoaza-15-crown-5 are reported in acetonitrile and ethanol. The amide link between the coumarin and the crown precludes pH sensitivity of the tertiary amine bridging group. Upon complexation by calcium and magnesium cations, the photophysical properties undergo marked changes, whereas the effects are insignificant or very weak with alkali metal ions. I.R. spectra were recorded in deuterated acetonitrile in order to unravel the participation of the carbonyl groups in the complexation. The stoichiometry of the complexes is 1:1 apart from the case of complexation with calcium in acetonitrile where two complexes can be formed. The stability constants of the complexes were determined in acetonitrile and ethanol.

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.

Photoinduced biprotonic transfer in 4-methylumbelliferone

Abstract Steady-state and time-resolved fluorescence studies of 4-methylumbelliferone in acidic ethanol—water and 1-butanol—water mixtures reveal that one water molecule is involved in the rate-limiting step of the phototautomerization process. It is shown that the intermediate species cannot be the cationic form as stated by other authors, but is most likely the anionic form. Moreover, it is concluded that the phototautomer is not zwitterionic but exists only in the neutral keto form. A biprotonic transfer mechanism is proposed.

Data analysis in frequency-domain fluorometry by the maximum entropy method — recovery of fluorescence lifetime distributions

Abstract The maximum entropy method has been applied to the analysis of data obtained from multifrequency phase-modulation fluorometry. Analysis of real data (mixtures of dyes, dye embedded in a rigid matrix) and simulated data (broad lifetime distribution) are presented for illustrating the efficiency of the method.

Ion-responsive fluorescent compounds: VI. Coumarin 153 linked to rigid crowns for improvement of selectivity

The photophysical and complexing properties of fluoroionophores consisting of the coumarin C153 linked to dibenzo-16-crown-5 (C153-DBC) and tribenzo-19-crown-6 (C153-TBC) are described in acetonitrile and ethanol. The carbonyl group of the coumarin moiety is in direct interaction with a bound cation. The selectivity of these compounds for a given alkali or alkaline earth metal ion was found to be better than that of previously reported crowned coumarins owing to the rigidity of dibenzo- and tribenzocrowns. In acetonitrile, a very high selectivity for Ca2+ versus Mg2+ has been found. In ethanol, C153-DBC is selective for Na+ and C153-TBC is selective for K+, as expected from the relative size of the crown cavity