Studies on the fluorescence quenching of anthracenes by polysilane copolymers

In this article, the room-temperature solution fluorescence quenching of electron-deficient anthracenes such as 9-cyanoanthracene (CNA), 9,10-dicyanoanthracene (DCNA), and 9,10-dichloroanthracene (DCLA) by polysilane copolymers was studied. The fluorescence quenching data was in conformity with the Stern-Volmer equation F₀/F = 1 + K_sv[Q], the F₀/F−[Q] straight lines were drawn, and the fluorescence quenching constants K_sv were obtained. By measuring the fluorescence lifetimes of the anthracenes, the fluorescence quenching rate constants k_q were calculated. Based on experiments and references, we tentatively proposed that for the same polysilane copolymer quencher the fluorescence quenching was caused mainly by the polysilane Si—Si chain and affected in a small degree by the side substituents attached to the Si—Si chain. In addition, it was observed that the order of the fluorescence quenching rate constants k_q of the above three electron-deficient anthracenes by the same polysilane copolymer was DCNA > CNA > DCLA, which is just in keeping with that of their electron deficiency. © 1996 John Wiley & Sons, Inc.     

Controlling the photoluminescence of water‐soluble conjugated poly[2‐(3‐thienyl)ethyloxy‐4‐butylsulfonate)] for biosensor applications

The photoluminescence of poly[2‐(3‐thienyl)ethyloxy‐4‐butylsulfonate)] (PTE‐BS) in aqueous solution increases threefold on addition of the surfactant tetrabutylammonium perchlorate (TBA). Furthermore, the luminescence of the PTE‐BS/TBA system is reduced by more than five times by the addition of small amounts of the cationic electron acceptor methyl viologen (MV²⁺). The Stern–Volmer constant K_SV = 1.4 × 10⁴ L mol^?1 for the quenching of the polymer–surfactant complex by MV²⁺ is approximately 60 times smaller than the K_SV = 8.4 × 10⁵ L mol^?1 obtained in water polymer solutions without surfactant. Thus, the luminescence of PTE‐BS in aqueous solution can be modulated by complexing the polymer either with a surfactant or with a quencher. In this contribution we show that the surfactant/quencher tuning effect found in polymers of the phenylenevinylene family, such as poly(2,5‐methoxy‐propyloxysulfonate phenylenevinylene), also appears in polymers of the thiophene family such as PTE‐BS. Copyright © 2007 Society of Chemical Industry     

Dynamic quenching of 5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (MEH-PPV) by charge transfer to a C60 derivative in solution

The fluorescence of 5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (MEH-PPV) quenched in solution in 1,2-dichlorobenzene by a soluble derivative of C₆₀ [1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C₆₁; [6,6]PCBM] is studied by changing the concentration of the quencher and by varying the temperature. For MEH-PPV and PCBM dissolved in 1,2-dichlorobenzene, the Stern–Volmer constant (K_SV) is 2 × 10³M⁻¹. At high temperature, K_SV is enhanced because thermal energy facilitates the diffusion of PCBM. The results show that dynamic quenching (rather than static quenching) is the basic mechanism. Comparison with data obtained from quenching studies of trans-stilbene indicates that a single acceptor in contact with an MEH-PPV macromolecule quenches the luminescence from hundreds of repeat units. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2553–2557, 2001     

Fluorescence quenching of poly(methylphenylsilane) in solution

The solution, electron-transfer fluorescence quenching of a typical aromatic polysilane[poly(methylphenylsilane)] by a series of electronic deficient aromatic monomers is described. The rate of fluorescence quenching is a function of the reduction potential of the quencher, and only very fast processes can be observed, due to the short polymer fluorescence lifetime. The measurement of quenching rate constants, which are considerably larger than diffusion control, suggests that extensive energy migration occurs in the polymer. Although the fluorescence quenching at low quencher concentrations follows Stern-Volmer kinetics, at high concentrations, contributions from static quenching are apparent. Strong fluorescence quenching can either accelerate or inhibit photodegradation, depending on the structure of the quencher.     

Determination of Quenching Inhibition Factor and Selective Fluorescence Quenching Study of Perylene,Pyrene and Fluoranthene in Micelle by Cetyl Pyridinium Chloride as a Hydrophobic Quencher Molecule

The fluorescence quenching study of perylene, pyrene and fluoranthene by cetyl pyridinium chloride (CPC) a hydrophobic quencher molecule has been carried out using synchronous fluorescence scan. A quenching inhibition factor (QIF) has been defined for added quencher in inert micellar medium. The other quenching parameters calculated are K _Q and E _Q . The obtained quenching parameter QIF well compares with these values. The quenching mechanism is found to be explainable by a quencher sphere of action model. In micellar medium the fluorescence quenching efficiency is in the order: pyrene > perylene > fluoranthene. A correlation between alternate and non-alternate PAHs and aromatic ring size with QIF has been reported for CPC in micelle.     

Enhancing performance of optical sensor through the introduction of polystyrene and porous structures

Simple and promising approaches for developing high‐performance Fe³⁺ sensors were proposed. Polyvinyl chloride (PVC) membrane containing pyrene as a fluorescent indicator was prepared via solvent‐cast method. Upon immersion into 1.0 mM Fe³⁺ solution, the fluorescence emission of the membrane decreased with the ratio of fluorescence intensities before and after (F₀/F) immersion of 1.25. The sensitivity enhancement was achieved through the introduction of polystyrene (PS) onto PVC and the introduction of porous structures. Polyvinyl chloride‐graft‐polystyrene copolymers (PVC‐g‐PS) were synthesized via Atom Transfer Radical Polymerization using PVC as macroinitiator. The grafting percentages of PS on PVC calculated from Nuclear Magnetic Resonance Spectroscopy were 17 and 41. The membrane prepared from low molecular weight copolymer showed higher sensing ability than that from PVC with the F₀/F value of 1.39. The increase in PS chain length did not significantly affect the fluorescence quenching. A Stern–Volmer quenching relationship was found with K_sv of 3.96 × 10² M^?1. The effect of porous structures on fluorescence quenching was studied by introducing Triton X‐100 as a porogen to PVC/pyrene solution. Attenuated total reflection Fourier transform infrared spectroscopy and Scanning Electron Microscopy analyses confirmed a complete removal of Triton X‐100 after 3 days of immersion in water. The porous membrane demonstrated an enhanced sensing performance with the F₀/F value of 1.46. PVC‐g‐PS/pyrene membrane exhibited highly sensitive and selective responses toward Fe³⁺ over Cu²⁺, Mg²⁺, Co²⁺, Zn²⁺, Ni²⁺, and Ag⁺. In addition, a good reversibility after five cycles of quenching and regeneration was obtained. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41759.     

Synthesis and photophysical properties of a novel green fluorescent polymer for Fe3+ sensing

BACKGROUND: In recent years, environmental pollution has become a major concern for industrial societies. The design of highly selective and sensitive sensor materials has become a very important scientific goal. RESULTS: A novel 4‐amino‐substituted 1,8‐naphthalimide dye with intense green fluorescence was synthesized. The dye was then copolymerized with methyl methacrylate. The presence of metal cations (Ca²⁺, Mg²⁺, Cr³⁺, Mn²⁺, Fe³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) could quench the fluorescence intensity of a tetrahydrofuran solution of the dye and the copolymer at different levels. The effect of Fe³⁺ was much stronger than that of the other cations. There was a good linear correlation between F₀/F (F₀ and F are the fluorescence intensities in the absence and presence of the metal ions, respectively) and the Fe³⁺ concentration in the range 1.33 × 10^?7–4.00 × 10^?4 mol L^?1. The polymeric sensor in a film state exhibited a dynamic response to Fe³⁺ in the concentration range from 3.44 × 10^?6 to 3.04 × 10^?3 mol L^?1 and the average response time was about 20 s. CONCLUSION: In view of the selectivity and rapid responsivity of the polymer sensor studied, it could be used as a new polymeric sensor for water pollution by Fe³⁺ cations. Copyright © 2008 Society of Chemical Industry     

Fluorescence study of interaction between an anionic conjugated polyelectrolyte and bovine serum albumin

The interaction between an anionic conjugated polyelectrolyte, poly[9,9-bis(3′-butyrate)fluoren-2,7-yl] sodium (BBS-PF), and bovine serum albumin was investigated by fluorescence spectroscopy. The emission of BBS-PF was effectively quenched by BSA with a quenching constant K _SV of 3.1 × 10⁷ L/mol when BSA was at nanomolar concentrations, but the emission increased when the concentration of BSA was at micromolar level. The excitation band of BBS-PF blue-shifted when the emission was quenched where the negatively charged BSA induced the aggregation of BBS-PF, yet the excitation band of BBS-PF red-shifted when the emission increased where the BSA acted as a surfactant and formed hydrophobic interaction with BBS-PF. BBS-PF could also quench BSA through energy transfer by resonance with a quenching constant K _SV of 1.1 × 10⁶ L/mol. The emission band changes of BSA reflected the conformation transitions of BSA from class II to class I and the binding of BBS-PF with BSA made the BSA more folded.     

Efficient preparation of novel fluoroalkyl end‐capped oligomers/titanium dioxide nanocomposites

Novel fluoroalky end‐capped oligomers/titanium dioxide nanocomposites were prepared by the hydrolysis of titanium isopropoxide in the presence of fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomer [R_F‐(DOBAA)_n‐R_F], fluoroalkyl end‐capped N,N‐dimethylacrylamide oligomer [R_F‐(DMAA)_n‐R_F], and fluoroalkyl end‐capped acrylic acid oligomer [R_F‐(ACA)_n‐R_F] in tetrahydrofuran under mild conditions. In these fluorinated oligomers, R_F‐(ACA)_n‐R_F oligomer is more effective for the preparation of the corresponding oligomers/titanium dioxide nanocomposites, and this oligomer can afford the expected fluorinated titanium dioxide nanocomposites in higher isolated yields. In addition, R_F‐(ACA)_n‐R_F/titanium dioxide composites are nanometer size‐controlled very fine nanoparticles (14–48 nm), and exhibited a good dispersibility not only in water but also in traditional organic solvents. Fluoroalkyl end‐capped oligomers/titanium dioxide nanocomposites were also applied to the surface modification of the common organic polymers such as poly(methyl methacrylate) to exhibit a good oleophobic and hydrophilic characteristics on the surface. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Synthesis and physicochemical characterization of amphiphilic block copolymer self‐aggregates formed by poly(ethylene glycol)‐block‐poly(ϵ‐caprolactone)

Diblock copolymers with different poly(ε‐caprolactone) (PCL) block lengths were synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of monomethoxy poly(ethylene glycol) (mPEG‐OH, MW 2000) as initiator. The self‐aggregation behaviors and microscopic characteristics of the diblock copolymer self‐aggregates, prepared by the diafiltration method, were investigated by using ¹H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy. The PEG–PCL block copolymers formed the self‐aggregate in an aqueous environment by intra‐ and/or intermolecular association between hydrophobic PCL chains. The critical aggregation concentrations of the block copolymer self‐aggregate became lower with increasing hydrophobic PCL block length. On the other hand, reverse trends of mean hydrodynamic diameters were measured by DLS owing to the increasing bulkiness of the hydrophobic chains and hydrophobic interaction between the PCL microdomains. The partition equilibrium constants (K_v) of pyrene, measured by fluorescence spectroscopy, revealed that the inner core hydrophobicity of the nanoparticles increased with increasing PCL chain length. The aggregation number of PCL chain per one hydrophobic microdomain, investigated by the fluorescence quenching method using cetylpyridinium chloride as a quencher, revealed that 4–20 block copolymer chains were needed to form a hydrophobic microdomain, depending on PCL block length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3520–3527, 2006     

Binding of Sulpiride to Seric Albumins

The aim of this work was to study the interaction of sulpiride with human serum albumin (HSA) and bovine serum albumin (BSA) through the fluorescence quenching technique. As sulpiride molecules emit fluorescence, we have developed a simple mathematical model to discriminate the quencher fluorescence from the albumin fluorescence in the solution where they interact. Sulpiride is an antipsychotic used in the treatment of several psychiatric disorders. We selectively excited the fluorescence of tryptophan residues with 290 nm wavelength and observed the quenching by titrating HSA and BSA solutions with sulpiride. Stern-Volmer graphs were plotted and quenching constants were estimated. Results showed that sulpiride form complexes with both albumins. Estimated association constants for the interaction sulpiride–HSA were 2.20 (±0.08) × 10⁴ M⁻¹, at 37 °C, and 5.46 (±0.20) × 10⁴ M⁻¹, at 25 °C. Those for the interaction sulpiride-BSA are 0.44 (±0.01) × 10⁴ M⁻¹, at 37 °C and 2.17 (±0.04) × 10⁴ M⁻¹, at 25 °C. The quenching intensity of BSA, which contains two tryptophan residues in the peptide chain, was found to be higher than that of HSA, what suggests that the primary binding site for sulpiride in albumin should be located next to the sub domain IB of the protein structure.     

Studies on the laser degradation of the CHCl3 solution of polysilane

In this paper, the XeCl excimer laser was used to irradiate the CHCl₃ solution of polymethylphenethylsilane (PMPES) and that of poly(dimethylsilane-co-methylphenethylsilane) (PDM-MPES). The laser energy absorbed by the polysilane macromolecules was measured, the gel permeation chromatography molecular weights of the polysilane macromolecules both before and after irradiation were determined, and their corresponding apparent quantum yields under the irradiation were calculated. The apparent quantum yield of laser degradation of the CHCl₃ solution of PMPES is two orders of magnitude larger than that of the CHCl₃ solution of PDM-MPES, indicating that the spatial obstruction of the substituents attached to the polysilane chains has great effect on its apparent quantum yield of laser degradation. For the polysilane photodegradation under a rather low laser energy, with the increase of the laser energy absorbed by the polysilane macromolecules, the average molecular weight after irradiation decreases gradually while the average scissions per macromolecule and the apparent quantum yield increase. The concentration of the CHCl₃ solution of polysilane has only small effect on its apparent quantum yield of laser degradation. According to the X-ray photoelectron spectroscopy analysis, the CHCl₃ solvent is involved in the photoreaction and combined into the dissociated product. In light of the references, it is preliminarily proposed that the laser degradation of the CHCl₃ solution of polysilane may result from the comprehensive action of such factors as homolytic cleavage, silylene extrusion, chain cleavage by reductive elimination, the radical chain transfer process, the fluorescence quenching of polysilane by CHCl₃, etc. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1515–1519, 1997     

Air filtration performance of nanofiber membranes with different morphologies produced by green electrospinning

To further target product development with low environmental impact, an integral green electrospinning (G-ES) approach has been adopted through the simultaneous application of various strategies, such as the use of biopolymers, reduction of energy use to avoid melting temperatures, and selection of non-toxic solvents and surfactants. Green solubility spinnability maps for cellulose acetate (CA), poly ε-caprolactone (PCL), and polyvinyl alcohol (PVA) are presented. Green electrospinning (G-ES) allows the production of new morphologies for CA and PCL nanofiber membranes. In this work, CA exhibits a ribbon-like morphology, PCL shows a honeycomb-like morphology and PVA cylindrical fibers. Membrane morphologies are compared with filtration efficiency (FE) for particle size of 1.0 μm and quality factor (Q_F) at a volumetric flux of 27.63 cm⁻¹. For CA is between 83% and 96% and high Q_F = 0.31–0.38 Pa⁻¹, PCL is 92% and 99% and high Q_F = 0.28–0.21 Pa⁻¹ and for PVA between 96% and 99% and high Q_F = 0.14–0.08 Pa⁻¹. These results suggest that the hierarchical nanofiber structure improves filtration performance because of the reduction in pressure drop and increase in PM interception. CA ribbon-like fibers favored air filtration performance, followed by PCL honeycomb-like fibers.     

Tunable emission color of Li2SrSiO4:Tb3+ due to cross‐relaxation process and optical thermometry investigation

A series of Li₂SrSiO₄:xTb³⁺ (0.2%, 0.4%, 0.6%, 0.8%, 2%, 4%, and 6%) phosphors were prepared by conventional solid‐state reaction. It was found that this silicate phosphor has a wide excitation band at near‐ultraviolet region (230‐300 nm) due to spin‐allowed 4f ⁸→4f⁷5d¹ transitions of Tb³⁺ ions, with the exact position dependent on the crystal field of the lattice. The cross‐relaxation process originating from ⁵D₃→⁵D₄ and ⁷F₆→⁷F₀ happened between different Tb³⁺ ions. It leads to the luminescence color of Li₂SrSiO₄: xTb³⁺ tuning from blue to green just by controlling Tb³⁺ concentrations. Furthermore, concentration quenching mechanism, energy migration type, cross‐relaxation rate and efficiency, are discussed in detail. Finally, optical thermometry properties were investigated via temperature‐dependent emission spectra. The results show that low‐concentration‐doped sample (Li₂SrSiO₄:0.4%Tb³⁺) shows remarkable optical thermometry based on fluorescence intensity ratio (FIR) between the blue and green emission of Tb³⁺ ions, whereas the high‐concentration‐doped sample (Li₂SrSiO₄:4%Tb³⁺) demonstrates small emission intensity loss. It illustrates that terbium‐doped silicate phosphor is a multifunctional material with potential application for display field and optical thermometry .     

Effect of Fluorine Ion on the Electrical Properties of Glasses in the Na2O–P2O5 System

The temperature–concentration dependence of the electrical conductivity of glasses in the NaPO₃–NaF system has been investigated. The regularities revealed are interpreted from the standpoint of the structural microinhomogeneity of glasses, which is due to the formation of polar structural units of the Na⁺[O^–POO_2/2], Na₂ ⁺[O^– ₂POO_1/2], Na⁺[F^–POO_2/2], and Na⁺F^– types. It is shown that the concentration dependence of the electrical conductivity is governed by the ratio between the concentrations of these structural units.     

Synthesis,characterization, and Pb2+ ion sensing application of hexa‐armed dansyl end‐capped poly(ε‐caprolactone) star polymer with phosphazene core

Novel hexa‐armed dansyl end‐capped poly(ε‐caprolactone) (PCL) star polymer with phosphazene core ( P2 ) was prepared via ring opening polymerization (ROP) and esterification reactions. P2 showed dual fluorescence emission when excited at 328 nm in acetonitrile : water (6 : 4) due to twisted intramolecular charge transfer (TICT) between dimethylamino and naphthalene units in the dansyl moiety. TICT emission band (A band) in the emission spectra red‐shifted with increasing solvent polarity. P2 responded to the addition of Pb²⁺, Hg²⁺, Co²⁺, Cd²⁺, Mn²⁺, and Zn²⁺ metal ions by decreasing TICT emission band with slight bathochromic shifts. The highest quenching efficiency was observed for Pb²⁺ ion with Stern–Volmer constant of 324.74M^?1. The Stern–Volmer plot for Pb²⁺ was rather linear with the increasing concentration of the quencher, indicating a dynamic (collisional) quenching mechanism. Stern–Volmer constants for Hg²⁺, Co²⁺, Cd²⁺, Mn²⁺, and Zn²⁺ ions were found to be 212.33, 189.21, 36.24, 20.84, and 20.69, respectively. Besides, the highest quenching efficiency (94.24%) was attained in the presence of Pb²⁺, suggesting that P2 could be employed as a potential Pb²⁺ chemical probe. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42380.     

Fast transient fluorescence technique (FTRT) for studying dissolution of polymer glasses

The fast transient fluorescence technique (FTRT) was used for studying the swelling and dissolution of a glassy polymer formed by free‐radical polymerization of methyl methacrylate (MMA). Anthracene (An) was introduced during polymerization as a fluorescence probe to monitor swelling and dissolution. Swelling and dissolution processes of disc‐shaped poly(methyl methacrylate) (PMMA) glasses in a chloroform–heptane mixture were monitored by measuring the fluorescence lifetimes of An from its decay traces. A method is developed for low quenching efficiencies for measuring lifetimes, τ, of An, and it was observed that τ values decreased as the dissolution process proceeded. Desorption, D, and mutual diffusion, D_m, coefficients of An molecules were measured during dissolution of PMMA and found to be around 5.4 × 10⁻⁶ (cm²/s) and 2.2 × 10⁻⁵ (cm²/s), respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 948–957, 1999     

Surface‐enhanced fluorescence of in situ synthesized polysilanesilver nanoparticles

To produce surface plasmons, silver nanoparticles are synthesized in situ in a pseudo‐template system based on polyhydrosilanes. Adsorption on the silver nanoparticle surface produces a thin layer of polymer with properties different from those of bulk polysilane. The metal‐adsorbed polymer layer serves as a spacer between the polysilane fluorophore and the plasmonic nanoparticle. This prevents quenching of the polysilane emission and leads to a strong surface‐enhanced fluorescence through coupling of surface plasmons having a resonance frequency that matches the emission frequency of the polymeric emitter. Copyright © 2012 Society of Chemical Industry     

Wettability of poly(ethylene terephthalate) film treated with low‐temperature plasma and their surface analysis by ESCA

The surface of poly(ethylene terephthalate) (PET) film was modified by low‐temperature plasma with O₂, N₂, He, Ar, H₂, and CH₄ gases, respectively. After being treated by low‐temperature plasma, their surface wettability and chemical composition were investigated by means of electron spectroscopy for chemical analysis (ESCA) and contact angle measurement. The result shows that the surface wettability of PET can be improved by low‐temperature plasma, and the effect of the modification is due mainly to the kind of the gases. Mainly because of the contribution of hydrogen bonding force γ[STACK]^c_S[ENDSTACK], the surface wettability of PET treated with O₂, N₂, He, and Ar plasma for a short time (3 min) increase sharply, and the surface wettability is also improved by H₂ plasma treatment; but the CH₄ plasma treatment does not improve the wettability of PET. ESCA shows that the effect of wettability of PET is tightly related to the presence of polar functional groups that reside in the outermost surface layer of PET. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1327–1333, 1999     

Thermal and spectroscopic studies of poly(N‐vinyl pyrrolidone)/poly(vinyl alcohol) blend films

Poly(N‐vinyl pyrrolidone) (PVP) and poly (vinyl alcohol) (PVA) homopolymers and their blended samples with different compositions were prepared using cast technique and subjected to X‐ray diffraction (XRD) measurements, infrared (IR) spectroscopy, ultraviolet/visible spectroscopy, and thermogravimetric analysis (TGA). XRD patterns of homopolymers and their blended samples indicated that blending amorphous materials, such as PVP, with semicrystalline polymer, such as PVA, gives rise to an amorphous structure with two halo peaks at positions identical to those found in pure PVP. Identification of structure and assignments of the most evident IR ‐ absorption bands of PVP and PVA as well as their blends in the range 400–2000 cm^?1 were studied. UV–vis spectra were used to study absorption spectra and estimate the values of absorption edge, E_g, and band tail, E_e, for all samples. Making use of Coats‐Redfern relation, thermogravimetric (TG) data allowed the calculation of the values of some thermodynamic parameters, such as activation energy E, entropy ΔS^#, enthalpy ΔH, and free energy of activation ΔG^# for different decomposition steps in the samples under investigation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009