Fluorescence enhancement of the europium-yttrium-diphacinone-ammonia system

A study of the enhanced (ca. 100 ×) fluorescence intensity of the Eu³⁺-diphacinone-ammonia system by Y³⁺ was made using a colloidal suspension. The excitation and emission wavelengths were 330 and 612 nm, respectively. The fluorescence intensity was a linear function of the concentration of europium in the range 6.0 × 10^?11–8.0 × 10^?7 M. The detection limit was 8.0 × 10^?14 M. The standard addition method was used for the determination of europium in rare earth oxides, with satisfactory results.     

Fluorescence enhancement of the Eu-Tb-benzoylacetone-phenanthroline system

The Eu-benzoylacetone-phenanthroline system, which has strong fluorescence intensity, was studied. It was found that the fluorescence intensity can be greatly increased by La, Gd, Tb, Lu and Y, Tb giving the greatest enhancement (ca. two orders of magnitude). The maximum fluorescence intensity was obtained at pH 8.0. Beer's law was obeyed from 1.0 × 10^?9 to 2.0 × 10^?7 M Eu. The detection limit for europium was 2.0 × 10^?11 M.     

Fluorescent magnesium(II) coordination polymeric hydrogel

A pH and mechano-responsive coordination polymeric gel was developed without the use of long chain hydrophobic groups. The hydrogel was synthesised by reacting the aqueous solution of Mg2+ with the basic aqueous solution of N-(7-hydroxyl-4-methyl-8-coumarinyl)-alanine. The gelation is attributed to the self-aggregation of 1D coordination polymers to form 3D nanostructures through non-covalent interactions to entrap water molecules. The freeze-dried hydrogel exhibits a fibrillar network structure with a uniform ribbon shape. UV/vis absorption studies illustrate that the hydrogel displays a typical pi-pi* transition. The fluorescence intensity of the hydrogel is enhanced drastically with a longer lifetime upon gel formation. Mechanical analysis including dynamic oscillation on shear, steady shear and creep (retardation-relaxation) testing have been performed to elucidate the supramolecular nature of the 3D assembly. Together with the viscoelastic properties and biocompatibility, the Mg2+ hydrogel may find utility as a novel soft material in biomedical applications.     

Nonlinear optically active polymeric coordination networks based on metal m-pyridylphosphonates

A family of polymeric coordination networks based on meta-pyridylphosphonate bridging ligands has been synthesized and characterized by single-crystal X-ray crystallography. Compounds [M(2)(L-Et)(4)(mu-H(2)O)] (M = Mn, 1; Co, 2; Ni, 3; L-Et = ethyl-4-[2-(3-pyridyl)ethenyl]phenylphosphonate) were obtained by hydro(solvo)thermal reactions between diethyl-4-[2-(3-pyridyl)ethenyl]phenylphosphonate (L-Et(2)) and corresponding metal salts, while [Cd(L-H)(2)], 4 (L-H is monoprotonated 4-[2-(3-pyridyl)ethenyl]phenylphosphonate), was obtained by a hydro(solvo)thermal reaction between (L-H(2)).HBr and Cd(CF(3)SO(3))(2).6H(2)O. Compounds 1-3 are isostructural and crystallize in noncentrosymmetric space group Fdd2, and they adopt a complicated 3D framework structure composed of [M(2)(L-Et)(4)(mu-H(2)O)] building units, while compound 4 adopts a centrosymmetric 3D network structure resulted from linking 1D sinusoidal cadmium phosphate chains with L-H bridging ligands. Consistent with their polar structures, compounds 1-3 exhibit powder second harmonic generation signals larger than that of potassium dihydrogen phosphate.     

Patterned polymeric multilayered assemblies through hydrogen bonding and metal coordination

Patterned polymeric multilayered assemblies were formed using a combination of metal coordination and hydrogen bonding interactions. We proved that the hydrogen bonding interaction between diamidopyridine and thymine can be employed for polymeric multilayer assemblies. We then combined this strategy along with a second supramolecular interaction, metal coordination. These interactions proved to be orthogonal to one another on the surface, making each discrete region individually responsive to external stimuli.     

The synthesis of a chemically reactive and polymeric luminescent gel

In the past, chemically reactive polymeric interfaces have been considered to be of potential interest for developing functional materials for a wide range of practical applications. Furthermore, the rational incorporation of luminescence properties into such chemically reactive interfaces could provide a basis for extending the horizon of their prospective utility. In this report, a simple catalyst-free chemical approach is introduced to develop a chemically reactive and optically active polymeric gel. Branched-polyethyleneimine (BPEI)-derived, inherently luminescent carbon dots (BPEI-CDs) were covalently crosslinked with pentaacrylate (5Acl) through a 1,4-conjugate addition reaction under ambient conditions. The synthesized polymeric gel was milky white under visible light; however, it displayed fluorescence under UV light. Additionally, the residual acrylate groups in the synthesized fluorescent gel allowed its chemical functionality to be tailored through facile, robust 1,4-conjugate addition reactions with primary-amine-containing small molecules under ambient conditions. The chemical reactivity of the luminescent gel was further employed for a proof-of-concept demonstration of portable and parallel ‘ON’/‘OFF’ toxic chemical sensing (namely, the sensing of nitrite ions as a model analyte). First, the chemically reactive luminescent gel derived from BPEI-CDs was covalently post-modified with aniline for the selective synthesis of a diazo compound in the presence of nitrite ions. During this process, the color of the gel under visible light changed from white to yellow and, thus, the colorimetric mode of the sensor was turned ‘ON’. In parallel, the luminescence of the gel under UV light was quenched, which was denoted as the ‘OFF’ mode of the sensor. This parallel and unambiguous ‘ON’/‘OFF’ sensing of a toxic chemical (nitrite ions, with a detection limit of 3 μM) was also achieved even in presence of other relevant interfering ions and at concentrations well below the permissible limit (65 μM) set by the World Health Organization (WHO). Furthermore, this chemically reactive luminescent gel could be of potential interest in a wide range of basic and applied contexts.

An unprecedented chemically reactive and polymeric luminescent gel is developed, and this material is further employed to develop a portable and rapid sensor for a practically relevant analyte (nitrite ions) with a sensitivity of 3 μM.     

Fluorescence enhancement of several hallucinogenic drugs in cyclodextrin media

The fluorescence characteristics of selected hallucinogenic drugs dissolved in solutions of α-cyclodextrin and β-cyclodextrin are reported. Fluorescence intensity enhancements in cyclodextrin media relative to aqueous solution range from 1.2 to 4.0, probably because inclusion of the drugs into cyclodextrin increases the quantum yield. Calibration graphs are linear over 2–3 orders of magnitude; limits of detection are 6–13 μg l^?1 for ibogaine and N,N-dimethyltryptamine. The mescaline derivatives show limits of detection in the 0.8–1.4 ppm range. The role of cyclodextrin in enhancing the fluorescence intensities and some of the criteria for this fluorescence enhancement are discussed.     

Characterization of the pore-surface gel phase in functionalized macroporous polymeric materials

Covalently immobilized pore-surface gel phases were prepared in a functionalized macroporous ultra-high-molecular-weight polyethylene by covalent coupling of lightly cross-linked polymer colloid particles [50% styrene, 49.8% (chloromethyl)stryrene, 0.2% divinylbenzene] to the interstitial pore surfaces. Swelling the covalently coupled colloid particles in a good solvent followed by chemical derivitization resulted in an immobilized pore-surface gel phase rich in primary amine groups. The macromolecular reactivity and molecular size-exclusion characteristics of the aminated pore-surface gel phase were then determined using monofunctional, amine-reactive, poly (ethylene glycol)s (PEG). Pegylated pore-surface gel phases that ranged from 71% (10,000 molecular weight PEG) to 56% (40,000 molecular weight PEG) PEG by weight resulted from reaction of the aminated gel phase with the PEG probe molecules. The number of PEG molecules reacting with the aminated pore-surface gel phase depends only on the Flory radius (or radius of gyration) of the PEG molecule to the negative 2.49th power i.e., 1/R _f ^2.49, corresponding to a M^−1.48 dependence. The immobilized and pegylated polymer colloid particles swell by a factor of 16–25 times the diameter of the original polymer colloid particles in water, thereby demonstrating that pegylation occurred though a substantial fraction of the volume of the immobilized colloid particles. Received: 18 January 1999 Accepted in revised form: 8 June 1999     

Fluorescence enhancement of mazindol in the presence of anionic surfactants

Experimental conditions for the determination of mazindol {[³H] imidazo(2,1-a)isoindol-5-ol-5(4 chlorophenyl-2,5 dihydro)} by u.v. spectroscopy and by spectrofluorimetry have been studied. We have found that the addition of anionic surfactants provides a four-fold increase in the sensitivity of the fluorimetric determination of mazindol at 325 nm. Sensitization parameters of each of the moieties of the anionic surfactant structures have been obtained and it has been found that the triethanolamine lauryl sulphate is the most adequate structure to produce an enhancement of the mazindol fluorescence. A new method for the fluorimetric determination of mazindol that involves prior u.v. irradiation of the samples is proposed which allows a sensitivity increase of 17,500% and a detection limit of 3.6 ng ml⁻¹.     

Fluorescence lifetime enhancement of organic chromophores attached to gold nanoparticles

We present for the first time experimental evidence of fluorescence lifetime enhancement of organic chromophores attached to metal nanospheres via radiative decay engineering. The hybrid system (HS) was a modified "diconjugated" molecular probe, 4-acetamido-4'-maleimidylstilbene-2,2'-dithiol (AMDT), covalently bound to the surface of 5-nm-diameter Au nanospheres by its two sulfur atoms, at a distance d < 1 nm and with its molecular axis parallel to the surface of the nanoparticle surface. We measured a fluorescence lifetime increase of a factor of 2 at room temperature (tau(AMDT) = (4.32 +/- 0.10) ns and tau(HS) = (8.73 +/- 0.23) ns) and a factor of 3.4 at 4.2 K (tau(AMDT) = (2.64 +/- 0.07) ns and tau(HS) = (7.96 +/- 0.14) ns). We also found that the fluorescence quantum yield of this hybrid system is not reduced, proof of a weak energy transfer between the molecular probe and the nanoparticle. These results demonstrate that a molecular dipole oriented parallel to the metal surface tends to be reduced by the coupling with its image.     

Fluorescence enhancement by gadolinium of the europium or samarium-dibenzoylmethane-diethylamine system

A fluorescence enhancement produced by adding Gd³⁺, Y³⁺, Tb³⁺, La³⁺ or Lu³⁺ to europium or samarium-dibenzoylmethane-diethylamine was observed. Gd³⁺ enhanced the fluorescence intensity by 2–3 orders of magnitude compared with the system without Gd³⁺. The new system was used for the simultaneous determination of traces of Sm³⁺ and Eu³⁺ in the ranges 1.0 × 10^?9?8.0 × 10^?8 M and 1.0 × 10^?11?4.0 × 10^?9 M, respectively, and the detection limits were 5 × 10^?13 M for Sm³⁺ and 8 × 10^?14 M for Eu³⁺. The luminescence mechanism of the system is discussed.     

ESR studies of coordination state of divalent copper ions anchored to polymeric supports

ESR studies of the interaction of Cu(acac)₂ anchored to various polymeric supports with model ligands CO and Py have revealed the effect of these interactions on the coordination state of divalent copper ions.

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Cu(acac)₂, , CO (py). .

     

Amino acid-based polymeric gel network and its application in different fields

Polymer gels are cross-linked polymeric matrix, having the ability to absorb a large volume of solvent molecules in their network structures. With inherent flexibility and adaptability along with stimuli-responsive behavior, polymer gels have been proven to be a very good candidate to find their potential applications in diverse fields including pharmaceuticals, biotechnology, female hygiene materials, drug delivery, wastewater treatment, cosmetics, etc. In recent times, significant number of efforts has been made to develop amino acid fabricated polymeric gel endowed with enhanced aqueous interaction. The inherent nature of the amino acid-based polymeric matrix facilitates the interaction with protein and gene along with the grafting ability to biological molecules. From the industrial point of view, the amino acid-based polymer gel is also viable because of low-cost starting materials, large scalability, etc. In the last decade, a significant amount of research was carried out on amino acid-based polymeric gel in the field of developing stimuli-responsive material, dye separation, oil-spill recovery, biomedical applications, and so on. In this review, we presented detailed insight into the synthesis strategies and applications of amino acid-based polymeric gels of the past decade (2005-present).     

A new three-dimensional polymeric PbII complex involving holo- and hemidirected coordination spheres

A new three-dimensional polymeric Pb^II complex, [Pb₃(bpy)(H₂O)₅(sip)₂]_n·0.5bpy·2H₂O (bpy = 2,2′-bipyridine and sip = 5-sulfoisophethalate), has been synthesized and characterized. Its single-crystal X-ray structure shows three types of Pb²⁺-ions with coordination numbers of 8 Pb1, 6 Pb2, and 7 Pb3. The Pb1 center with a coordination number of 8 possesses a stereo-chemically ‘inactive’ electron lone pair, and the coordination sphere is holodirected. However, the arrangement of O- and N-atoms for Pb2 and Pb3 suggests a gap or hole in the coordination geometry around these atoms. The stereo-chemically ‘active’ electron lone pairs of Pb2 and Pb3 possibly occupy these ‘holes’, and their coordination spheres are, thus, hemidirected.     

Water-assisted self-assembly of harmonic single and triple helices in a polymeric coordination complex

A novel two-dimensional coordination polymer containing infinite, coherently pitched single and triple helical motifs is formed by the self-assembly of Cd2+, succinate, water and a bipyridyl ligand.     

Fluorescence enhancement effect and the interaction between donor and acceptor

A new theoretical equation for fluorescence enhancement effect between donor and acceptor has been introduced.By using it we determined the binding constants and numbers of binding sites of five medicines,including chlorogenic acid,forsythiaside norfloxacin,Ciprofloxacin and fluorenone,to γ-globulin.     

Fluorescence enhancement by heterostructure colloidal photonic crystals with dual stopbands

In this work, we present a facile approach on the remarkable enhancement of fluorescent signal by heterostructure colloidal photonic crystals (PCs) with dual stopbands. The intensity of fluorescent medium on heterostructure PCs with dual stopbands overlapping the excitation wavelength and the emission wavelength of fluorescent medium can be up to 162-fold enhancement in comparison to that on the control sample. Otherwise, parameters of heterostructure PC films such as film thickness or stacking order have important effects on fluorescent signals. The method will be of great significance for developing the highly sensitive fluorescence-based detection.     

Fluorescence enhancement by symmetry breaking in a twisted triphenylene derivative

1,4,5,8,9,12-hexamethyltriphenylene (HMTP) shows a high photoluminescence quantum yield (PLQY) of 31% in the solid state, making it of interest for luminescence applications. The detailed photophysical properties of HMTP have been investigated by using time-resolved and steady-state luminescence, PLQY, and molar absorption coefficient measurements. An enhancement of the transition dipole moment for fluorescence and absorption was demonstrated compared to the case of unsubstituted triphenylene, which resulted in a 20-fold increase in the radiative decay rate. This is attributed to a breaking of triphenylene symmetry as a result of the necessarily twisted structure induced by steric crowding. In addition, it was shown that HMTP shows similar photoluminescence energies in solution, powder, and film, indicating a reduced propensity for intermolecular π-stacking compared to the case of triphenylene, as a result of this twisted structure. This work also develops a method for calculating the photoluminescence quantum yield of powders by using a calibrated photodiode in combination with an uncalibrated CCD spectrometer.     

Fluorescence enhancement at hot-spots: the case of Ag nanoparticle aggregates

We report the enhancement of the fluorescence emitted from dye-labeled DNA upon co-aggregation with silver nanoparticles. The co-aggregation process is induced by the polycationic molecule spermine, which both neutralizes the charge of the DNA backbone and aggregates the nanoparticles. This simple method generates nanoparticle aggregates with very short (1-2 nm) inter-particle distance. Even though no spacer layer was used, large enhancements of the fluorescence, in the range of 15-740× (depending on the original quantum yield of the dye used), were observed. Theoretical modeling shows that this occurs as the local enhancement of the electromagnetic field near the hotspots is sufficiently large to overcome the quenching by the surface, even at short distances of 1 nm. The predicted trend of increased SEF enhancement with a decrease in initial quantum yield is observed. The average enhancements observed in this system are on-par with the best results obtained on nanostructured surfaces to date.