New Europium(III)-TTA Complex Containing 2-Pyrrolidone as Coligand to Application as Luminescent Sensor: PbII and Ethanol in Gasoline

This work describes the synthesis and application of an europium(III) complex, [Eu(TTA)3(2-pyr)(H2O)], containing 2-thenoyltrifluoroacetonate (TTA) and 2-pyrrolidone (2-pyr) as ligands, obtained as white solid and soluble in ethanol. In solution, the complex showed red emission, characteristic of the EuIII emission in the solid state (λexc = 375 nm and λem = 612 nm). The complex was tested with PbII, CdII, and HgII ions in water. The effect of metal ions was monitored and evaluated by hypersensitive transition 5D0 → 7F2 (612 nm). The results show that PbII suppresses the complex luminescence and present high sensitivity, according to the values for the Stern-Volmer constant (KSV = 2300 L mol-1), showing good linearity, i.e., determination coefficient (R2) of 0.9913, and low limit of detection (LOD = 6.03 µM). Luminescence quenching increased with the increasing concentration of PbII. These results indicate that the synthesized complex is a potential luminescent sensor for detecting PbII in a simple and fast way, being applicable for routine environmental analysis. When applied as an ethanol sensor in gasoline, the complex hypersensitive transition intensity decreased with the increasing volume of ethanol in gasoline, reaching the values of R2 = 0.9815 and LOD = 4.94% v/v.

Plasmonic-Ceria Nanoparticles as Fluorescence Intensity and Lifetime Quenching Optical Sensor

Ceria nanoparticles have been recently used as an optical fluorescent material with visible emission under ultraviolet excitation, due to the formation of trivalent cerium ions with corresponding oxygen vacancies. This paper introduces the enhancement of both fluorescence emission and lifetime through adding gold nanoparticles. The reason is due to possible coupling between the plasmonic resonance of gold nanoparticles and the fluorescence emission of ceria that has been achieved, along with enhanced formation of trivalent cerium ions. Both factors lead to higher fluorescence intensity peaks and shorter fluorescence lifetimes. As an application, gold-ceria nanoparticles have been used as an optical sensing material for lead particles in aqueous media based on fluorescence quenching. Stern-Volmer constant of in-situ gold-ceria nanoparticles is found to be 2.424 M−1, with a relative intensity change of up to 40% at 0.2 g/L.

A novel luminescent hybrid material based on zinc complexes and graphene oxides for detection of Fe3+ in aqueous media

A novel GOS-modified zinc complex probe with water dispersibility is designed to detect Fe3+ in aqueous media (Stern–Volmer constant KSV = 4 × 106 L mol−1).

Label-Free and Sensitive Detection of BRCA1 and TB4 DNA Sequences with Water-Soluble Cationic Polythiophenes

A sensitive method for BRCA1 and TB4 DNA sequences detection using water-soluble cationic polythiophenes, poly(3-(1′-ethoxy-2′-N-methyl imidazole)thiophene) (PT) is presented. The fluorescence of PT could be dramatically quenched by the addition of single-stranded DNA (ssDNA; TB4 and BRCA1 sequences). The KSV (Stern–Volmer constant) for TB4 and BRCA1 DNA sequences are 1.46 × 108 and 3.28 × 108 M–1 respectively, and the limits of detection of these two sequences are 1.26 × 10–10 and 0.483 × 10–10 M respectively. The fluorescence of PT would recover to its initial intensity after the addition of complementary ssDNA, whereas sequences with one to three mismatched bases would not. The influences of buffer pH and concentration of NaCl were also investigated systemically in order to further improve the sensitivity. This assay can be completed in a short period of time without any further procedure. Hence, this sensitive, cost-effective, and rapid detection method for BRCA1 and TB4 DNA sequences may contribute to the clinical diagnosis of breast cancer gene mutations in the future.

Colorimetric Detection of Nitroaromatics Using Organic Photochromic Compounds

An organic photochromic compound is explored as a new portable colorimetric sensor for nitroaromatics. This photochromic compound switches from colourless to pink upon exposure to ultraviolet light. In the presence of nitroaromatic explosive derivatives the photoswitching behaviour of the dithienylethene is suppressed, while a potential false positive (toluene) has little effect. The degree of photoswitching inhibition was determined by comparing the integrated visible absorption with the concentration of the analyte to give the pseudo Stern–Volmer constant (KPSV). The KPSVs measured varied from 12900 (p-nitrotoluene) to 236 M–1 (toluene), which were directly related to the analyte absorption at the excitation wavelength.

Significant sensitivity and stability enhancement of tetraphenylporphyrin-based optical oxygen sensing material in presence of perfluorochemicals

Emission-based oxygen sensing properties of highly luminescent tetraphenylporphyrin molecules were investigated in polystyrene, ethyl cellulose, poly(1-trimethylsilyl-1-propyne) and poly(isobutylmethacrylate) matrices. The effect of perfluorochemicals (PFCs) on oxygen sensitivity and stability of the sensor materials was also examined. Fluorescence intensity and lifetime measurements of meso-tetraphenylporphyrinato Zn ( II ) (ZnTPP) and meso-tetraphenylporphyrin (H2TPP) materials were performed in the concentration range of 0–100% pO 2. The fluorescence intensity variation of H2TPPvs. oxygen was 86%. H2TPP-based composite also yielded higher Stern–Volmer constant, faster response and regeneration time, excellent long term photostability and larger linear response range with respect to ZnTPP. The detection limit of oxygen for H2TPP was less than 0.5%. When stored in sealed bags protected from sunlight, no decrease in oxygen sensitivity was observed during approximately five months. As far as we know, the gathered utilization of PFCs and H2TPP embedded in polymer matrices was not previously described in literature, and has present amelioration compared to materials already existing.

Fluorescence Quenching by Reversible Charge Separation Followed by Ions Recombination and Their Separation Suppressed by Coulomb Attraction

The Stern-Volmer constant is specified for the luminescence quenched by reversible ionization of excited molecules. The exergonic branch of the Rehm-Weller free energy dependence of this constant is known to be a plateau determined by irreversible ionization being under diffusion control. In the endergonic region the ionization is reversible and competes with the irreversible in-cage recombination of ions and their escape from the cage. At strong Coulomb attraction the latter phenomenon is shown to be negligible compared to the former that determines the shape and location of the descending branch of the Rehm-Weller curve. At weaker Coulomb attraction (at higher solvent polarity), this curve turns down at larger endergonicity. The experimental data obtained in solvents of different polarities are put in order and in full accordance with present theory.

Laser flash photolysis study of the photochemistry of ortho-benzoylbenzaldehyde

Ketene-enols 4 and 5 have been generated by laser flash photolysis of ortho-benzoylbenzaldehyde (3) and kinetically and spectroscopically characterized. In benzene or acetonitrile, the E ketene-enol, 4, shows absorption at 340 and 400 nm and a lifetime in excess of 1 ms, whereas the Z ketene-enol, 5, shows maxima at 360 and 430 nm and a lifetime of only 1.5 μs. At shorter time scales we observed a weak absorption (λmax = 580 nm) tentatively assigned to biradical 6 with a lifetime of 140 ns. The E ketene-enol is readily quenched by oxygen, dienophiles, methanol, and water, with quenching rate constants ranging from 3.6 × 103 M−1 s−1 (for methanol as a quencher) to 2.2 × 108 M−1 s−1 (for diethylketomalonate). At high water concentrations (typically > 10 M) a new species, 7, was detected showing maximum absoiption at 510 nm and a growth lifetime of 7 μs. In deuterated water and using the same concentration as before we observed a formation lifetime for 7 of 10 μs, which results in an isotope effect of ~ 1.5. It is proposed that 5 is the main precursor for 7. Steady-state irradiation of 3 in deaerated methanol leads to the formation of dihydroanthraquinone (9), a strongly colored and fluorescent (λmax = 475 nm, τn = 29 ns) species, whereas 3-phenylphthalide (2, R = Ph) is the main product when the irradiation is performed in benzene. Steady-state quenching of product formation by diethyl ketomalonate gives a Stern–Volmer constant of 380 M−1 from which we conclude that 5 is the ketene-enol responsible for product formation, in agreement with the laser flash photolysis results.