Extracting decay curves of the correlated fluorescence photons measured in fluorescence correlation spectroscopy

We have developed a new method to extract the decay curves of the correlated fluorescence photons from the data of fluorescence correlation spectroscopy using time-correlated single photon counting. In this method, a two-dimensional correlation map of photon pairs is generated at an absolute delay time with reference to the excitation-emission delay of each photon. Using a dye-labeled DNA as an example, we have demonstrated that the decay curve of the correlated fluorescence photons is separated from the uncorrelated background signals simply by subtracting a two-dimensional correlation map at sufficiently long delay time without additional prior information.     

Determination of the molecular distribution in anisotropic media by polarized absorption and emission spectroscopy

A theory for the interpretation of polarized absorption and emission spectra of uniaxially oriented samples, including overlap of different polarized transitions in both processes, is described. Using this method for the interpretation of experimental data, the distribution of molecules possessing different geometrical anisotropy, incorporated in stretched polyethylene films, and the partial contribution of different polarized transitions to the total emission intensity can be estimated.     

Absorption and fluorescence of 2,5-diarylidenecyclopentanones in acidic media: evidence for excited-state proton transfer

Spectroscopic properties for a series of 2,5-diarylidenecyclopentanones in weak and strong acid environments are reported. Electronic absorption and fluorescence spectra have been measured for the all-E configurations of 2,5-dibenzylidenecyclopentanone (1), 2,5-bis(3-phenylallylidene)cyclopentanone (2), and 2,5-bis(5-phenylpenta-2,4-dienylidene)cyclopentanone (3) in acetic acid and sulfuric acid solutions. The spectroscopic evidence indicates that in 96% sulfuric acid 1, 2, and 3 are protonated both in the ground state and on the S1 potential energy surface. This assignment is supported by Zerner's intermediate neglect of differential overlap (ZINDO) and time-dependent density functional theory (TD-DFT) calculations. In glacial acetic acid, 1, 2, and 3 are unprotonated in the ground state. The absence of observable fluorescence from 1 in glacial acetic acid indicates that S1 is npi, whereas the observation of fluorescence from 2 and 3 in acetic acid is consistent with S1 being pipi. A combination of spectroscopic data, molecular orbital calculations, and fluorescence lifetime measurements indicate that 2 and 3 undergo intermolecular excited-state proton transfer in glacial acetic acid and diluted sulfuric acid solutions. Photochemical studies reveal that, unlike its behavior in organic solvents, 1 does not undergo efficient E,E --> E,Z photoisomerization in 96% sulfuric acid.     

Absorption and emission spectroscopy of molecular trimers: Cyclic versus linear geometries

The spectroscopic properties of molecular trimers are studied within a model where three degenerate electronically excited states are coupled via dipole–dipole interactions. Taking a single vibrational degree of freedom for each monomer into account, this results in a non-adiabatic nuclear dynamic which determines features of the spectra. The cases of a cyclic and a linear coupling scheme are regarded and it is investigated how these different geometries influence the absorption and emission spectra.     

Absorption and fluorescence properties of aryl substituted porphyrins in different media

Absorption and fluorescence properties of aryl substituted porphyrins, 5,10,15,20-tetra-4-oxy(aceticacid)phenylporphyrin (TAPP), 5,10,15,20-tetra-(4-phenoxyphenyl) porphyrin (TPPP), 5,10,15,20-tetra-(3-bromo-4-hydroxyphenyl) porphyrin (TBHPP), and 5,10,15,20-tetra-p-chloromethylphenyl porphyrin (CMPP) were investigated. The UV/vis absorption, fluorescence and excited spectra as the fluorescence quantum yields and fluorescence lifetimes for the compounds were measured in organic solvents (chloroform (CHCl₃), tetrahydrofuran (THF)) and immobilized media (PVC film, sol–gel matrix). The fluorescence quantum yields of TAPP and TPPP were higher than the others. The fluorescence lifetimes of all studied porphyrin derivates were found to be fifty percent lower and their fluorescence intensities were increased fifty percent more in both of immobilized mediums, as compared to organic solvents.     

Time-resolved spectroscopy of long-path fluorescence and scattering for measuring total absorption of fluids

Optical methods are appropriate tools to detect organic micro-pollutants in fluids. A new technique is introduced which uses the decay of interaction processes like fluorescence and elastically scattered radiation by a fluid. Principally two different parameters are determined:

1. (i) the decay-time of the conventional interaction τ_C, which occurs at relatively short path-lengths of the incidence beam in the fluid, and

2. (ii) the decay-time τ_MP of the multi-path-saturation interaction originating at long path-lengths, e.g. in multi-path-reflection cuvettes, where the incidence beam is fully absorbed by the fluid.

A relation between the decay-time and the absorption coefficient of a fluid is theoretically derived. A simple preliminary experiment is performed considering distilled water polluted with non-fluorescent azobenzene and fluorescent quinine-sulphate. A nitrogen laser has been used to generate the fluorescence and scattering signals. The reciprocal value of the difference between the decay-time of the multi-path and conventional signals, 1/(τ_MP − τ_C), yields the total absorption coefficient directly. In comparison to the conventional absorption technique the decay-time method is characterized by a higher sensitivity.     

Absorption and fluorescence spectroscopy of rhodamine 6G in titanium dioxide nanocomposites

A comparison has been made between the spectroscopic properties of the laser dye rhodamine 6G (R6G) in mesostructured titanium dioxide (TiO(2)) and in ethanol. Steady-state excitation and emission techniques have been used to probe the dye-matrix interactions. We show that the TiO(2)-nanocomposite studied is a good host for R6G, as it allows high dye concentrations, while keeping dye molecules isolated, and preventing aggregation. Our findings have important implications in the context of solid state dye-lasers and microphotonic device applications.     

Exciplex fluorescence emission from simple organic intramolecular constructs in non-polar and highly polar media as model systems for DNA-assembled exciplex detectors

Organic intramolecular exciplexes, N-(4-dimethylaminobenzyl)-N-(1-pyrenemethyl)amine (1) and N'-4-dimethylaminonaphthyl-N-(1-pyrenemethyl)amine (2), were used as model systems to reveal major factors affecting their exciplex fluorescence, and thus lay the basis for developing emissive target-assembled exciplexes for DNA-mounted systems in solution. These models with an aromatic pyrenyl hydrocarbon moiety as an electron acceptor appropriately connected to an aromatic dimethylamino electron donor component (N,N-dimethylaminophenyl or N,N-dimethylaminonaphthyl) showed strong intramolecular exciplex emission in both non-polar and highly polar solvents. The effect of dielectric constant on the maximum wavelength for exciplex emission was studied, and emission was observed for 1 and 2 over the full range of solvent from non-polar hydrocarbons up to N-methylformamide with a dielectric constant of 182. Quantum yields were determined for these intramolecular exciplexes in a range of solvents relative to that for Hoechst 33,258. Conformational analysis of 1 was performed both computationally and via qualitative 2D NMR using (1)H-NOESY experiments. The results obtained indicated the contribution of pre-folded conformation(s) to the ground state of 1 conducive to exciplex emission. This research provides the initial background for design of self-assembled, DNA-mounted exciplexes and underpins further development of exciplex-based hybridisation bioassays.     

Study of polymer complexes by size exclusion chromatography coupled with light scattering in combination with fluorescence spectroscopy

Poly(methyl methacrylate) stereocomplexes prepared at different concentration in dilute tetrahydrofuran solutions were studied by size exclusion chromatography coupled with refractive and light scattering detectors in combination with fluorescence spectroscopy. A considerable increase in segment density due to complexation compared with free poly(methyl methacrylate) chain was only slightly affected by the polymer concentration in solution where stereocomplexes were formed. At polymer concentrations up to 3×10⁻³ g cm⁻³, an increase in non‐uniformity of polymer complex molecular weight and size and a shift to higher values of both were observed. In semidilute solutions (at c > 3×10⁻³ g cm⁻³) stereocomplexes virtually did not become heavier and larger.     

Absorption,fluorescence and resonance Rayleigh scattering spectral characteristics of interaction of gold nanoparticle with safranine T

Gold nanoparticle is an important nanomaterial and has been investigated widely owing to its special physical and chemical property[1―5]. In recent years it has been found that the multiple-component nano- structure assembly containing metal, semiconduct…     

Excitation emission and time-resolved fluorescence spectroscopy of selected varnishes used in historical musical instruments

The analysis of various varnishes from different origins, which are commonly found on historical musical instruments was carried out for the first time with both fluorescence excitation emission spectroscopy and laser-induced time-resolved fluorescence spectroscopy. Samples studied include varnishes prepared using shellac, and selected diterpenoid and triterpenoid resins from plants, and mixtures of these materials. Fluorescence excitation emission spectra have been collected from films of naturally aged varnishes. In parallel, time-resolved fluorescence spectroscopy of varnishes provides means for discriminating between short- (less than 2.0 ns) and long-lived (greater than 7.5 ns) fluorescence emissions in each of these complex materials. Results suggest that complementary use of the two non destructive techniques allows a better understanding of the main fluorophores responsible for the emission in shellac, and further provides means for distinguishing the main classes of other varnishes based on differences in fluorescence lifetime behaviour. Spectrofluorimetric data and time resolved spectra presented here may form the basis for the interpretation of results from future in situ fluorescence examination and time resolved fluorescence imaging of varnished musical instruments.     

A chemiluminescence and fluorescence spectroscopy study: An investigation of photocrosslinking processes in polymer systems

Chemiluminescence emission is shown to be a valuable method for the analysis and monitoring of the photochemical transformation process in BZMA-co-S copolymers. BZMA-co-S copolymer films are synthesized and irradiated at λ > 400 nm, in order to induce the phototransformation of benzyl (BZ) to benzoyl peroxide (BP) pendant groups, resulting in thermal decomposition and crosslinking. The chemiluminescence emission increases with irradiation time, and is shown to be related to the benzoyl peroxide moieties generated during irradiation. The increase in chemiluminescence intensity is interrupted at longer periods of irradiation, when the concentration of these species tends to a nearly constant value. In this case, others factors are considered to influence the chemiluminescence emission, for example the increasing crosslinking on irradiated samples, which would restrict the mobility of radicals to recombine due to crosslinking of the network.A good correlation between fluorescence, FTIR and CL measurements during photochemical formation and thermal decomposition of peroxides is found. In this work, an intramolecular excimer forming fluorescent probe, DiPyM, is also used to analyse the crosslinking process. The results obtained contribute significantly to the development of chemiluminescence as a highly sensitive methodology for assessing the photocrosslinking of a polymeric material in the early stages of the process and is due to its sensitivity in comparison to that of fluorescence analysis.     

Partitioning behaviour in aqueous two-phase systems and fractionation by counter-current distribution of chick-embryo erythrocytes with numerical resolution of distribution curves

The partition of chick-embryo and young-chick erythrocytes in dextran-poly-(ethylene glycol) two-phase systems depends on the interfacial tension and electrical potential differences between the phases. Counter-current distribution with charged 5% dextran-poly(ethylene glycol) systems has proved to be an adequate method for the separation of primitive and definitive erythrocytes present in chick embryos when a phase settling time of 20 min is used. The computer-aided numerical resolution of experimental curves has shown the existence of subpopulations which could not have been detected by using conventional methods.     

Analysis of trace metals in water by in-situ sample pre-concentration combined with wavelength dispersive X-ray fluorescence spectroscopy and inductively coupled plasma-optical emission spectroscopy

In this paper an earlier work on the use of poly(acrylamidoxime) cloth for use as a passive monitor for trace metals in water by characterizing the sorption of several metals onto the cloth using a continuous flow chamber is extended. The monitors consists of amidoxime chelating groups covalently bound to the surface of a textile encased in a common 35 mm slide holder. Placement of this device in the water to be sampled resulted in the uptake of heavy metals by the chelating groups. After removal of the monitor from water, the metals were analyzed using wavelength dispersive X-ray fluorescence spectroscopy (WDXRF) as well as by acid extraction followed by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Correlation between the two methods of analysis varied with maximum correlation of 0.99897 observed for Pb and a minimum correlation of 0.16512 for Mg. The order of the distribution coefficients for the seven metals tested was: Pb> or =Cu>Zn>Cd>Mn>Fe>Mg, in agreement with the order of the stability constants for the amidoxime/hydroxamic acid group for the chelation of the same metals at a pH of 5, with the exception of Fe. Field testing of the monitors was also carried out and a comparison made between active sampling of river water and sampling with the monitors. Results indicated that semiquantitative analysis of trace metals in water may be performed using the passive monitors.     

Absorption and emission spectroscopy and magnetic susceptibility of sodium β-alumina doped with Mn,Co, and Ni

The absorption spectrum and magnetic susceptibility vs temperature have been measured for β-alumina doped with Mn, Co, and Ni. In addition, the emission spectra of Mn-doped samples have been measured. Mn and Co are shown to occupy tetrahedral sites and to be in the +2 oxidation state in β-alumina, in agreement with the results of previous investigators. Nickel is shown to occupy both octahedral and tetrahedral sites in β-alumina. Evidence indicates that nickel on octahedral sites is in the +3 oxidation state while that occupying tetrahedral symmetry sites is in the +2 oxidation state. The bands in the absorption spectrum for each metal are assigned and Dq, B, and C are calculated where possible.     

Necessary and sufficient conditions for the appearance of extrema on concentration distribution curves in complex equilibrium systems

It is shown that species distribution curves with at least one minimum may be found in most equilibrium systems with three or more components. Whether such concentration minima are actually observed then depends on the values of the equilibrium constants and on the total (analytical) concentrations of the components. A general algorithm is given for the necessary and sufficient conditions for the appearance of extrema in multicomponent systems. Three-component systems are studied in more detail and special attention is given to the limiting case of a horizontal inflection, i.e., the point where the concentration minimum just disappears. Two well-studied chemical examples, the Cu(2+)-diethylenetriamine-OH(-) and Hg(2+)-Cl(-)-OH(-) systems are discussed, along with a simple model system showing as many as five extrema on a single distribution curve.     

Determination of homogeneous vibronic spectra and the inhomogeneous distribution function of impurity molecules in solids by fluorescence saturation

Methods are developed for determining homogeneous vibronic spectra and the inhomogeneous distribution function of impurity molecules in low-temperature solid matrices by optical saturation of no-phonon transitions. The possibilities are demonstrated with solid solutions of perylene in benzophenone and n-hexane at 4.2 K.     

Preparation and characterization of polymer layer systems for validation of 3D Micro X-ray fluorescence spectroscopy

For the validation of the quantification of the newly-developed method of 3D Micro X-ray fluorescence spectroscopy (3D Micro-XRF) samples with a low average Z matrix and minor high Z elements are best suited. In a light matrix the interferences by matrix effects are minimized so that organic polymers are appropriate as basis for analytes which are more easily detected by X-ray fluorescence spectroscopy.     

Twist angle dependent mesomerism and spectroscopy in substituted anilines: Absorption and fluorescence spectra of indoline derivatives as planar model compounds

Absorption and emission spectra of 5-cyano-N-alkyl-indolines have been compared to those of the corresponding p-cyano-N,N-dialkylanilines, and the red shift and anomalously low absorption coefficient of the indolines analysed in terms of a molecules-in-molecules (MIM) model. The widely applied cos² θ equation relating oscillator strength and intramolecular twist angle θ is shown to be inadequate for near planar geometries in this case.The observation of an isoemissive point in the fluorescence spectra of the indolines indicates the existence of a ground state conformational equilibrium. Fluorescence and excitation anisotropy are discussed in terms of a vibronic coupling mechanism.     

Comparison of atomic fluorescence and atomic emission spatial distribution profiles in the inductively coupled plasma

Extensive maps of fluorescence from calcium neutral atoms and ions have been measured. These measurements have been made using a readily available commercial torch (MAK Torch, Sherritt Research Centre, Fort Saskatchewan, Alberta, Canada) which has rigidly controlled dimension specifications in order to facilitate interlaboratory comparisons. The measurements were made for ground state Ca atoms and ions (15 point radial profiles) for each of five heights (10,13,19,25 and 31 mm above the load coil), four powers (0.75,1.0,1.25 and 1.5 kW) and three carrier gas flow rates (1,0.85 and 0.65 l/min). In addition complete lateral emission profiles of these same species have also been measured over the same range of conditions. The Ca atomic fluorescence and emission results are compared and as well the fluorescence results for the Sr ion are compared with ICP-mass spectrometric results. Finally, atomic fluorescence and emission results are presented for the Mo atom; these are contrasted with those for the Ca atom and preliminary results for the resonance fluorescence of excited state calcium ion are also presented.