Optical chemosensors for metal ions in aqueous medium with polyfluorene derivatives: Sensitivity, selectivity and regeneration

Six polyfluorene derivatives, P1-P6, were synthesized and investigated as responsive materials for the optical sensing of metal ions in an aqueous medium. They were designed by combining carbazole with fluorene units within the backbone. Carbazole was N-functionalized with three coordinating groups, 2-pyridyl-benzimidazole (P1 and P4), 2-phenyl-benzimidazole (P2 and P5) and 4-phenyl-terpyridyl (P3 and P6), respectively. P1-P3 are random copolymers with fluorene:carbazole ratios of 9:1 for P1 and P2, and 9.7:0.3 for P3; P4-P6 are the corresponding alternating polymers. This design lead to polymers made of a conjugated backbone and pendant coordinating groups. The optical properties of the monomers were impacted in various ways by metal ions, and the formation of the [NiM3]2+ and [ZnM3]2+ and [ZnM32]2+ were evidenced with association constants of 105.22, 106.45 and 1014.0, respectively. The emission of the polymers was afterwards found to be influenced by theses metal ions with different sensitivity and selectivity. P1 was found to be more sensitive to the Ni2+ and Cu2+ ions with a better selectivity for Ni2+. Emission of the corresponding alternating polymer P4 was more efficiently quenched by these two ions with respect to P1, in addition of being sensitive to the Ca2+ and Al3+ ions. P3 showed sensitivity to the Ni2+, Cu2+, Al3+, Ca2+, and Zn2+ ions. The luminescence of P6 was much more pronounced with the Ni2+, Cu2+, Cd2+, Zn2+, Al3+, Fe2+, and Fe3+ ions with respect to P3. More remarkably, the presence of the Zn2+ or Cd2+ ions resulted in a new emission band, leading to the possibility to selectively sense these two ions. Relatively high Stern-Volmer constants (in the 106-105 range) were obtained, and sensitivities down to the ppb level were reached, especially for the Ni2+ ion. Influence of both the coordinating group and the polymer backbone on the polymers sensitivity and selectivity was emphasized. Finally, the recyclability of some representative optical sensors was shown both in solution and in the solid state. In particular, thin films were shown to be easily regenerated, which opens the way to the elaboration of reusable optical sensors

Size evolution of onion structure under oscillatory shear flow

The formation process of onion structure in a quaternary mixture among water, NaCl, octanol and sodium dodecyl sulphate, have been investigated by two dimensional light scattering under oscillatory shear flow. In our experiment, we investigated the size evolution of onion structure estimated by light scattering data with a nonlinear least-squares curve fitting method. The time evolution of onion size showed a good agreement with a stretched exponential function. The effect of oscillatory shear flow on formation process of onions is briefly discussed from the viewpoint of the physical meaning of fitting parameters based on the integral transformation method

Polymorphism Control of DBDCS in a Microfluidic System and Characterization by its Fluorescent Lifetime

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The effect of gold nanoparticle capping agents on 1O2 detection by singlet oxygen sensor green

International audienceSinglet Oxygen Sensor Green (SOSG) is the most widely used fluorescent probe for detecting singlet oxygen (1O2). 1O2 can be efficiently produced by exciting the surface plasmon of gold nanoparticles with laser pulses. However, gold nanoparticles are usually embedded in a chemical stabilizer that can interact with SOSG, leading to erroneous detection of 1O2. This article shows that the emission properties of SOSG strongly depend on the concentration of cetyltrimethylammonium bromide (CTAB), a capping agent widely used for nanoparticles synthesis and stabilization. The sensitivity of SOSG to 1O2 is also drastically affected by the presence of CTAB. This effect is due to the fluorescent probe's aggregation in CTAB premicellar aggregates and micelles, and the emergence of fluorescent conformers of the probe in the micelles. Furthermore, the behavior of SOSG in the presence of two other widely-used capping agents, i.e., citrate and Polyethylene Glycol (PEG), is investigated to determine the right nanoparticle stabilizer to use with SOSG probe

On the temperature dependence of the quenching by a few defects of TADF materials. Triplet versus Singlet FRET

International audienceThermally Activated Delayed Fluorescence (TADF) molecules contribute to the light emission of an optoelectronic device from both their singlet and triplet states. But the quenching limits these benefits. In the case of cationic (NHC)Cu(I) complexes bearing 2,2’-dipyridylaminei solids, we have studied the quenching mechanism, the exciton mobility and its energy transfer efficiency as a function of temperature. We can create defects in crystals of TADF molecules by a strong laser irradiation. The quenching efficiency by these defects depends on the temperature.This is because the repartition between the singlet and triplet states depends on the temperature and the singlet state is more prone to quenching through the FRET. From the analysis of the decay curves, we show that the excitons are not mobile in the crystal. We also show that the quenching is through FRET. We show that the quenching is due to the small number (<3) of defects inside the quenching volume

Unravelling the true MOF-5 luminescence

International audienceHighly pure millimeter-sized MOF-5 single crystals were synthesized and characterized. Photoluminescence (PL) spectroscopy and time-correlated single photon counting (TCSPC) demonstrate a solvent-guest dependency of MOF-5 emission and its ligand-centred nature. These results allowmeasuring the true MOF-5 luminescence free of solvent at a wavelength of 355 nm, a significantly lower wavelength than previously published. MOF-5 emission was also evaluated with different solvents and various degrees of water intake, explaining previously published observations. Comparison between lifetimes shows the fluorophore stabilization within the frameworks and demonstrates the progressive influence of the Zn4O subunits on the fluorescence during hydration. Overall, this work highlights the necessity to obtain phase-pure material, especially when moisture sensitivity can play a role, before ascribing electronic transitions. This study is a rigorous new take on the iconic MOF-5 and on its photoluminescence properties

On the temperature dependence of the quenching by a few defects of TADF materials. Triplet versus Singlet FRET

International audienceThermally Activated Delayed Fluorescence (TADF) molecules contribute to the light emission of an optoelectronic device from both their singlet and triplet states. But the quenching limits these benefits. In the case of cationic (NHC)Cu(I) complexes bearing 2,2’-dipyridylaminei solids, we have studied the quenching mechanism, the exciton mobility and its energy transfer efficiency as a function of temperature. We can create defects in crystals of TADF molecules by a strong laser irradiation. The quenching efficiency by these defects depends on the temperature.This is because the repartition between the singlet and triplet states depends on the temperature and the singlet state is more prone to quenching through the FRET. From the analysis of the decay curves, we show that the excitons are not mobile in the crystal. We also show that the quenching is through FRET. We show that the quenching is due to the small number (<3) of defects inside the quenching volume