Pyrene fluorescence quenching by aromatic azides

Pyrene fluorescence quenching by phenylazide derivatives with donor and acceptor substituents has been studied by fluorescence spectroscopy and flash photolysis. The rate constants of quenching (k _q) in acetonitrile ((0.2–1.2) × 10¹⁰ l mol^?1 s^?1) are found to be close to a diffusion limit; the rate constants were somewhat higher for perfluoro-substituted arylazides. It is found that k _q does not depend on solvent polarity; the formation of the pyrene cation in the course of pyrene fluorescence quenching by tolylazide was not detected. Pyrene fluorescence quenching occurred by an energy-transfer mechanism; this is supported by the coincidence of the quantum yields of the direct and sensitized photodecomposition of tolylazide. As estimated, energy transfer in rigid media occurs at characteristic distances of about 10 Å.     

The fluorescence quenching rate constant for the distance-dependent quenching processes in the presence of diffusion

It is shown that the fluorescence quenching constant is given by the Laplace transform of the time-dependent bimolecular rate constant k(t). The dependence of the quenching rate constant on the transformation parameter can be obtained from measurements of the fluorescence decay functions and a Stern-Volmer-type analysis in the Laplace domain. The advantages of this type of investigation of the quenching rate function are demonstrated by a numerical calculation for the distance-dependentquenching process in     

Enhanced conjugated polymer fluorescence quenching by dipyridinium-based quenchers in the presence of surfactant

Poly[(2-methoxy-5-propyloxysulfonate)phenylene vinylene] (MPS-PPV) was synthesized directly from its bischloromethylated monomer, considerably reducing the total number of steps involved in the polymer preparation. For the first time, a simple technique of ultracentrifugation was employed for final purification of the polymer. The interactions among the polymer, surfactant, and quencher molecules, as well as amplified fluorescence quenching and fluorescence enhancement associated with the interactions, were investigated and discussed. When compared with methyl viologen [MV]2+, higher values of Stern-Volmer constant K(SV) values on the order of > or =10(7) M(-1) were observed for the newly synthesized N-(2-carboxyhexadecanoyl)-N'-methyl-4,4'-bipyridinium iodide bromide ([CHMB]2+) quencher in the presence of 1,2-dioleoyl-3- trimethylammonium propane (DOTAP) surfactant. Comparisons of surfactants demonstrated that the K(SV) of [CHMB]2+ was 10-fold higher in the presence of dodecyltrimethylammonium bromide (DTAB) surfactant than with DOTAP. Polymer fluorescence was totally recovered upon addition of DOTAP surfactant to a MV-quenched polymer system, whereas only 50% of fluorescence was recovered upon addition of DOTAP surfactant to the CHMB-quenched polymer solution. In contrast, no fluorescence was recovered when DTAB was added to either the MV- or CHMB-quenched polymer systems. Thus, fluorescence enhancement was observed for the polymer complex with DOTAP, whereas fluorescence quenching was predominant in the polymer complex with DTAB. Such studies will not only help to better understand the intrinsic properties of the ionic conjugated polymer and amplified fluorescence quenching and enhancement but also provide guidelines to develop the next generation of ionic conjugated-polymer-based biosensors.     

Pyrene fluorescence quenching and triplet-state formation in the presence of DABCO (1,4-Diazabicyclo[2-2-2]octane): A laser photolysis study

In this paper, we present a study of fluorescence quenching of pyrene by DABCO in cyclohexane solutions. The absorption spectra of pyrene singlet state ¹S-ⁿS have been measured in the presence and in the absence of DABCO; the spectra are practically identical. The de-excitation of singlet pyrene by DABCO seems to be a non-reversible process leading to the triplet state, the probability of formation of this triplet state being near unity in the quenching process.     

Static and dynamic model for 4-aminodiphenyl fluorescence quenching by carbontetrachloride in hexane

The fluorescence quenching of 4-aminodiphenyl (4ADP) with chloromethanes (CH2Cl2, CHCl3 and CCl4) have been studied in solvents of different polarity and viscosity. The quenching rate constants (kq) have been determined in all solvents. For CCl4 and CHCl3 quenching, the kq depends on solvent viscosity whereas for CH2Cl2, the kq values show a mixed trend with no clear-cut variation with either solvent polarity or solvent viscosity. Quenching mechanism involving an intermediate donor-acceptor complex formation is proposed for CH2Cl2 quenching. A positive deviation was observed in the Stern-Volmer (SV) plot for CCl4 quenching in hexane. The static-dynamic model could explain this.     

Magnetic quenching of fluorescence

The direct and indirect mechanisms for the magnetic enhancement of radiationless decay processes are described, and used to account for the experimental observations of the magnetic quenching of fluorescence from carbon disulphide, glyoxal, and nitrogen dioxide.     

The size of sodium dodecyl sulfate micelles in the presence ofn-alcohols as determined by fluorescence quenching measurements

The steady-state fluorescence quenching technique was used to investigate the effect of the presence of a series of alcohol homologues of mid-sized straight chain on the size of mixed micelles of sodium dodecyl sulfate (SDS). We used pyrene at concentration of ca. 10^–6M, where only its monomer exhibits any fluorescence, as fluorescent probe, and cetylpiridinium chloride at concentrations in the range (1–9)×10^–5 M as quencher. This technique allows one to determine the micellar aggregation number. The number of alcohol molecules per micelle was calculated from reported values for the micelle-water partition coefficient. On the assumption of spherical micelles, their hydrophobic radii was then calculated. The hypothesis that micelle size is determined by the available surface area per charged headgroup is discussed in the light of the results obtained.     

Stimulated fluorescence and fluorescence quenching in chlorophyll a and bacteriochlorophyll a

This communication deals with the photophysical processes that take place in chlorophyll solutions under intense nitrogen laser irradiation. The effect of the pump photon density on the fluorescence yield depends strongly on the geometry of the irradiation and the sampling set-up. If the fluorescence cell and sampling probe are placed close to the transverse arrangement used for obtaining laser output, line narrowing and gain, which are processes associated with high population inversions and stimulated fluorescence, are observed. A normal fluorescence spectrum and a decrease in fluorescence quantum yield with increasing pump power are observed in the fluorescence cells in oriented at an angle of 20–40° with respect to the transverse axis of the exciting beam. The decrease in quantum yield appears to result from absorption of the pump photons by the excited singlet of the chlorophylls, and it is suggested that an analogous mechanism may be responsible for the anomalous fluorescence quantum yield reported for in in vivo Chlorella vulgaris algae.     

The quenching of chlorine fluorescence in the gas phase

Laser induced fluorescence has been observed from the B³Π(O⁺_u) state of chlorine. Lifetimes have been measured from 19 to 208 Pa, but the radiative lifetime is too long to be extracted from the data. A rate coefficient of 3.2 × 10[su13] cm³ mol?1 s?1 was measured for quenching by Cl₂ or Ar, the removal process being collision induced predissociation of the ³Π(O⁺_u) state.     

Oxygen quenching of delayed fluorescence in the solid state

A gradual increase in delayed fluorescence intensity is observed in crystalline 2-chloroanthracene and 9,10-diphenylanthracene in air under irradiation with light of constant intensity in the first triplet band. Detailed measurements in 2-chloroanthracene of delayed fluorescence intensity and triplet exciton lifetime show that the behavior is consistent with a triplet exciton-oxygen interaction which results in a depletion of the ground-state molecular oxygen concentration in the lattice and leads to a time dependence of the triplet exciton lifetime and of the effective S₀ → T₁ absorption coefficient of the material.     

荧光猝灭法测定次黄嘌呤及机理研究

研究了次黄嘌呤猝灭伊文思蓝的荧光猝灭机理并根据次黄嘌呤对伊文思蓝荧光的猝灭作用建立了测定次黄嘌呤的新方法.线性回归方程为:ρ=6.292×103F-1-26.49,相关系数为0.9990,线性范围为0.20～20.0 μg/mL,检出限为0.14 μg/mL,相对标准偏差(RSD)为2.5%.求算了伊文思蓝与次黄嘌呤的形成常数K=2.63×102L/moL,实验了pH、放置时间、干扰离子等对测定的影响.     

Measurement of glucose using fluorescence quenching

A new spectroscopic procedure for the measurement of glucose concentrations is described which is based on substrate induced quenching (SIQ) of an indicator fluorescence. The method exploits a novel photo reaction between thionine and NADH, the latter being generated due to the reduction of NAD⁺ in an enzymic reaction between glucose dehydrogenase (GDH) and glucose. The observed SIQ data was analysed using an empirical relation. A quenching constant of 1.8×10³ (±100) M⁻¹ is obtained for the substrate induced quenching of thionine by glucose. The reported method, which was investigated over the range 0–1000 μM, offers a glucose detection limit of 2.2 μM. Various applications of the proposed scheme are discussed, including its use to construct a fibre optic biosensor for glucose.     

Determination of nucleic acids by near-infrared fluorescence quenching of hydrophobic thiacyanine dye in the presence of Triton X-100.

A near-infrared (near-IR) fluorescence quenching method was developed for the determination of nucleic acids in aqueous solution by using a cationic heptamethylene thiacyanine as a probe. The near-IR cationic cyanine showed maximum excitation and emission wavelengths at 800 and 825 nm, respectively, in the presence of Triton X-100; the fluorescence of the cyanine could be greatly quenched by DNA. The calibration graphs were linear over the range of 10-400 ng/mL for CT (calf thymus) DNA and over the range 5-400 ng/mL for FS (fish sperm) DNA under optimal conditions. The corresponding detection limits were 5.2 ng/mL for CT DNA and 2.5 ng/mL for FS DNA. The relative standard deviation (n = 8) was 3.1% for 75 ng/mL CT DNA and 2.2% for 75 ng/mL FS DNA, respectively. Preliminary research showed that the fluorescence quenching might be ascribed to the formation of dye aggregate facilitated by DNA.     

Thioamide quenching of intrinsic protein fluorescence

Thioamides quench tryptophan and tyrosine fluorescence in a distance-dependent manner and thus can be used to monitor the binding of thioamide-containing peptides to proteins. Since thioamide analogs of the natural amino acids can be synthetically incorporated into peptides, they can function as minimally-perturbing probes of protein/peptide interactions.     

Pyrene fluorescence measurements of metastable oil droplets in surfactant-free oil-in-water emulsions

 The fluorescence behavior of pyrene in oil droplets of a surfactant-free oil-in-water emulsion was studied for benzene, fluorobenzene, n-hexane and cyclohexane droplets in water. The excimer–monomer fluorescence ratio immediately after sonication, I _E/I _M(0), of the benzene/water emulsion was 8–10 times larger than for the benzene solution. The ratio I _E/I _M(t) increased in the first 10–20 min before it decreased to zero. Similar behavior was observed for the fluorobenzene/water emulsion, while I _E/I _M(0) for emulsions with n-hexane and cyclohexane was smaller than for benzene and fluorobenzene/water emulsions. I _E/I _M(t) hardly changed with time for the n-hexane and cyclohexane/water emulsions. This different behavior was attributed to the increased solubility of nanometer-size droplets with benzene and fluorobenzene. Received: 20 June 2001 Accepted: 19 April 2001     

Structural and fluorescence quenching characterization of hematite nanoparticles

Nanoparticles of the dominant hematite form (α-Fe(2)O(3)) of iron oxide have been prepared by a simple route of dropping FeCl(3) solution into boiling water. The nanoparticles have been characterized by transmission electron microscopy (TEM), UV-visible electronic absorption spectroscopy, chemical stoichiometry, thermal analysis methods (TGA, DSC and DTA), XRD, FTIR and magnetic susceptibility measurements. Kinetic analysis of the DSC calorigram of thermal dehydration of the nanoparticles reveals one stage of the dehydration process of energy of activation of 29.0 kJ mol(-1). The role of iron oxide nanoparticles in fluorescence quenching of coumarin thiourea derivatives (I-IV) was investigated at room temperature (296 K) by means of steady-state fluorescence spectroscopy. The quenching process was characterized by Stern-Volmer (S-V) plots which display a positive deviation from linearity. This could be explained by static and dynamic quenching models. The positive deviation in the S-V plot is interpreted in terms of ground-state complex formation model and sphere of action static quenching model. Various rate parameters for the ?uorescence quenching process were determined by using the modi?ed Stern-Volmer equation. The sphere of action static quenching model agrees very well with experimental results. Quenching constants for iron oxide nanoparticles are about four orders of magnitudes higher than quenching by Fe(3+) ions.     

荧光熄灭法测定微量氟的研究和应用

在环境监测中微量F~-的分析受到很大的重视.过去采用了分光光度法、离子选择电极法和荧光光度法,前两种方法选择性好,但灵敏度略低;荧光光度法灵敏度较高,可直接测定简单样品中的微量氟.在测定氟的荧光方法中,均是采用荧光熄灭法.此法的特点是灵敏度高,但操作繁琐,很少用于实际样品分析.我们研究了氟的几个新体系,从中筛选出灵敏度高、操作简便的锆-8-羟基喹啉-5-磺酸体系.在水溶液中测定,1μg F~-使体系荧光强度下降68％,与文献报道的体系相比是较高的.本法灵敏度为0.002μgF~-/mL,是测定氟的最灵敏方法之一.     

Migration of excitation energy and fluorescence quenching in regular lattices

Intermolecular transfer of excitation energy is studied in model systems containing luminescent donor molecules (D) and acceptor molecules (A) which constitute deep energy traps. It has been assumed that the donor and acceptor molecules form a regular lattice in which the energy transfer takes place in a hopping manner. Within the limits of the model, it has further been assumed that elementary processes are responsible for the deactivation of excited donor molecules (D^*). These processes are: fluorescence, internal conversion and non-radiative energy transfer D^* → D and D^* → A. The general considerations concern the partial and total fluorescence quantum yield of the system and the number of energy transfers before its deactivation. A more detailed analysis and calculations, leading to analytical expressions describing these quantities, have been made for linear systems. It is shown, that has approach, under the conditions where in the system only the migration of energy is observed and no other means of energy deactivation exist leads to the same value of the average number of energy transfers as was obtained earlier by Montroll and a mean relaxation time as given by Movaghar et al.     

Fluorescence quenching and laser photolysis of dipyrrolylbenzenes in the presence of chloromethanes

Fluorescence quenching of 1,4-bis(1H-pyrrol-1-yl)benzene, 1-(1H-pyrrol-2-yl)-1-(1-vinyl-1H-pyrrol-1-yl)benzene, and 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene with chloromethanes (methylene chloride, chloroform, and carbon tetrachloride) in solvents with different polarities follows electron-transfer mechanism. The occurrence of an electron-transfer step is confirmed by formation of short-lived pyrrolylbenzene radical cations. An exception is quenching of fluorescence of 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene in n-hexane in the presence of CCl₄ and CHCl₃ and in pure CCl₄. In this case, neutral 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene^·-Cl radical is formed via recombination of 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene radical cation and chloride anion. A relation was found between the nature of the short-lived species detected by laser photolysis and stable product obtained by stationary photolysis.