Quantitative study of fluorescence excitation and emission spectra of bean leaves

A quantitative and comprehensive knowledge of leaf fluorescence is required for the interpretation of fluorescence signals at the canopy level and also for the modelling of leaf and canopy fluorescence. In this work we present full range fluorescence excitation and emission spectra of intact leaves, expressed in units of apparent spectral fluorescence yield, from both the adaxial and the abaxial sides of the leaves, and for both front-side and back-side geometries. Emission spectra were measured for incident radiations in the blue and the green spectral range. The red/far-red fluorescence ratio depended on the measurement geometry and on the excitation wavelength. Excitation spectra were measured for emissions at 687 and 760 nm. When the abaxial side was illuminated, the measured spectra always had a larger intensity compared to adaxial side that is explained by the higher scattering of the spongy tissues. At 760 nm, the spectra had the same shape for front-side and back-side geometry, indicating that scattering predominated. At 687 nm, the shape of the spectra was very different for front-side and back-side geometry due to re-absorption of red fluorescence within the leaf. The comparison of excitation spectra measured from the adaxial or the abaxial side revealed differences in carotenoid absorption.     

The effect of fluctuations on emission spectra: practical distinctions between raman and fluorescence spectra

By the use of stochastic theory it is clearly shown that two types of emission should to fluctuations such as would occur during interactions with their environment are resonantly driven by light. In our approach the electromagnetic field is treated in a classical manner and decay is introduced by a Wigner-Weisskopfansatz. The two types of emission should occur for a three-level system and relaxation to other levels is not involved in the mechanism. Also included is a discussion of operational definitions of fluorescence (and other spontaneous emissions) and of the relationship between absorption and scattering in terms of dephasing or T₂ processes, especially as this relates to conventional emission phenomena.     

Resolved fluorescence emission spectra of PRODAN in ethanol/buffer solvents

The fluorescence steady-state emission spectra of lipophilic fluorescence probe PRODAN in ethanol/buffer solvents of different concentrations (0.3, 0.9, 3 mol L(-1) ethanol) were extensively studied and analytically described. The complex experimental spectra, corrected for background effects, were fitted by two Gaussian curves. The energy separation of two maxima, (0.147+/-0.002) eV at 37 degrees C and (0.143+/-0.003) eV at 25 degrees C, was independent of ethanol concentration. The blue shifts observed for both maxima were linearly dependent on solvent polarity. The linear dependences of fluorescence's intensities on PRODAN concentration in all ethanol/buffer solvents indicate that no PRODAN self-quenching takes place even at the highest measured PRODAN concentrations.     

Comparison of several background compensation methods useful for evaluation of energy-dispersive X-ray fluorescence spectra

A number of background estimation and modelling strategies suitable for evaluating energy-dispersive X-ray spectra by means of non-linear least squares fitting are evaluated and intercompared. As background modelling functions, exponential and linear combinations of mutually orthogonal polynomials are considered. These functions allow the shape of the background to be determined together with the photopeak intensities. As background estimation algorithms, an iterative stripping algorithm and a background channel selection procedure which is also based on the use of orthogonal polynomials are studied. The last two methods calculate the spectral background prior to the actual fitting process. For the intercomparison, the various methods were incorporated in the software package AXIL (Analysis of X-ray spectra by means of Iterative Least Squares). By using simulated spectra in which the intensity of all lines is a priori known, the accuracy and noise-sensitivity of the different background compensation strategies are evaluated. The method in which the background is modelled as a linear combination of orthogonal polynomials is identified as being the most robust and yielding the most accurate results.     

Semiempirical methods applied to long-wave satellites in X-ray emission spectra

Conclusions The following conclusions are drawn. Calculations from the CI model improve the interpretation of the observed x-ray spectra by comparison with the one-electron approximation. The two compounds show strong correlation effects for the internal MO, which agrees with the picture established in the literature of restricted applicability for the one-electron HF approximation.This method of analyzing the long-wave satellite structure on the basis of 2 hp configurations alone gives qualitative agreement with the available evidence for CO and SO₂ and evidently incorporates most of the correlation interactions.When one extends the MO basis in the CI calculations, one can describe much of the correlation effect for the outer MO. Consequently, one can use this model for qualitative or semiquantitative evaluation of long-wave satellite structures and multielectron limits arising from interaction between closely spaced 2hp configurations in the final state in the x-ray transitions, which appear in the x-ray spectra for coordination compounds. It is particularly important to determine the multielectron limit for a coordination compound because measurements are used in drawing conclusions on the bond types, reactivities, and ligand interactions [39, 40], where one considers also the form of the long-wave part of the spectrum.Institute of Inorganic Chemistry, Siberian Branch, USSR Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 2, pp. 80–91, March–April, 1989.     

Dual fluorescence of the isoquinolinium cation in methanol: time-resolved emission spectra and semiempirical calculations

The fluorescence behavior of the N-ethyl isoquinolinium (iso-NEQ) cation in viscous methanol is reported and discussed on the basis of time-resolved fluorescence spectra, polarization measurements and semiempirical calculations. Dual fluorescence results from two nearby excited states (S₁ and S₂) above 300 nm only at low temperature. The detection of an isoemissive point verifies this two-state model of the emission. We use the numerical self-consistent reaction field (SCRF) to include solute–solvent interactions for the calculations of the absorption transitions of iso-NEQ in methanol. We also involved the so-called supermolecular approach with three methanol molecules to reproduce the absorption transitions. The latter results are in good agreement with our experimental data.     

"Self-immolative" spacer for uncaging with fluorescence reporting

Dual photoliberation: A caged, branched, self-immolative spacer (see scheme, gray box) was designed to rapidly and simultaneously release a desired compound (green) and a fluorophore?(red) upon photoactivation. Careful kinetic analysis of the disassembly of the spacer shows that it occurs on the shortest time scale reported to date.     

Characterization of spilled oils by measuring fluorescence emission spectra of fractions separated by high-speed gel-permeation chromatography

Summary Fluorescence emission spectra of oil fractions separated by high-speed gel-permeation chromatography (GPC) were measured to characterize the oils spilled into the environment. Crude oils, weathered crude oils, and tar balls were analysed. In GPC, polystyrene gel and tetrahydrofuran were used as a stationary phase and a mobile phase, respectively; the eluate was separated into five equi-volume fractions. Fluorescence emission spectra of the fractions were obtained at an excitation wavelength of 340 nm. Maximum emission wavelength, relative emission intensity at 386 nm, and emission intensity ratio (440 nm/386 nm) on the spectra of fractions were studied as identification parameters. The change of the identification parameters with weathering the crude oil (Murban) was small. The proposed method was applied to the characterization of tar balls sampled in the sea near Japan.

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Charakterisierung von Ölverschmutzungen durch Auswertung der Fluorescenz-Emissionsspektren von Fraktionen, die durch Hochgeschwindigkeits-Gelpermeations-Chromatographie getrennt wurden

Zusammenfassung Rohöle, verwitterte Rohöle sowie Teerballen wurden untersucht. Bei der Chromatographie wurde Polystyrolgel als stationäre und Tetrahydrofuran als mobile Phase verwendet. Das Eluat wurde in fünf Fraktionen gleichen Volumens getrennt. Für die Fluorescenzmessung wurde eine Anregungswellenlänge von 340 nm benutzt. Als Identifizierungsparameter dienten die maximale Emissionswellenlänge, die relative Emissionsintensität bei 386 nm sowie das Verhältnis der Emissionsintensitäten bei 440/386 nm. Die Veränderung der Parameter bei der Verwitterung (Murban-Öl) war nur gering. Die Methode wurde zur Charakterisierung von Teerballen angewendet, die aus dem Meer in der Nähe Japans entnommen worden waren.

     

Metal-enhanced fluorescence exciplex emission

In this letter, we report the first observation of metal-enhanced exciplex fluorescence, observed from anthracene in the presence of diethylaniline. Anthracene in the presence of diethylaniline in close proximity to Silver Island Films (SIFs) shows enhanced monomer and exciplex emission as compared to a non-silvered control sample containing no silver nanoparticles. Our findings suggest two complementary methods for the enhancement: (i) surface plasmons can radiate coupled monomer and exciplex fluorescence efficiently, and (ii) enhanced absorption (enhanced electric near-field) further facilitates enhanced emission. Our exciplex studies help us to further understand the complex photophysics of the metal-enhanced fluorescence technology.     

Ultraviolet emission spectra of sunbeds

It is well known that UV radiation contributes to the development of skin cancer. Exposure to solar radiation is predominantly responsible for the high incidence rate of skin cancer, but there are also indications that sunbeds are involved. The aim of the present investigation was to determine the UV emission spectra of sunbeds. It included the most common sunbed models, which cover more than 50% of the Swiss market. The UV emission spectra of sunbeds have special characteristics and are different from the sun spectrum, which can be seen in high-resolution spectral measurements. Sunbed emission spectra are similar to the sun spectrum in the UVB (280-320 nm) range but reach values 10 to 15 times higher in the UVA (320-400 nm) range. An average erythema-effective irradiance of 0.33 W/m2 was determined for sunbeds. This corresponds to a UV index of 13, which is significantly higher than the UV index of 8.5 of the high summer sun at noon at intermediate latitudes. The measurements were spread over the whole effective area of the sunbeds, and an inhomogeneous distribution of the irradiances with variations of up to 30% from the average value was found.     

Algebraic methods for molecular rotation-vibration spectra

Algebraic techniques similar to those recently introduced in nuclear physics may be useful in the treatment of molecular Spectra. A spectrum generating algebra appropriate to diatomic molecules is constructed. This algebra, U(4), is the simplest generalization to 3-D of the algebra of the 1-D Morse oscillator and a simplification of the U(6)algebra of nuclear rotation-vibration spectra.     

Ionization constants and fluorescence excitation and emission spectra of the isomeric benzo[a]pyrene phenols

The acid dissociation constants, for the ground and lowest excited singlet states of the benzo[a]pyrene phenols, are reported, and correlated with current thought on carcinogen activation. The corrected fluorescence excitation and emission spectra of these compounds and their anions are recorded. The shifts caused by ring hydroxylation of the parent compound, and the relative spectral band intensities for each phenol are compared to those of pyrene, in a brief assessment of spectral transition polarization in the phenols.     

Silicon-substituted rhodamines for stimulated emission depletion fluorescence nanoscopy

As an essential part in the toolbox of super-resolution microscopy, stimulated emission depletion(STED)nanoscopy has been widely explored in revealing the substructure and bioactivities in fluorescence imaging. Among the applied STED fluorophores, silicon-substituted rhodamines(SiRs) belong to one of the most extensively employed fluorophores. The carboxy-SiR was favored in STED bioimaging with many advantages, including reliable photostability, cell permeability, tunable fluorogenicity, feasibl...     

New regioisomeric naphthol-substituted thiazole based ratiometric fluorescence sensor for Zn2+ with a remarkable red shift in emission spectra

Ratiometric fluorescent chemosensors based on the position of ring annulation of the naphthol–thiazole moiety for quantification of zinc ions in aqueous ethanol were synthesized and investigated. It was found that sensor 3 exhibited a remarkably large red shift of 140 nm in emission upon complexation with Zn²⁺. A TD-B3LYP/6-31G (d,p) calculation was performed to characterize the nature of the fluorescence behavior of sensor 3 upon Zn²⁺ complexation. The combination of experimental and computational analyses provides a more complete understanding of the molecular level origin of these unique photophysical properties of this type of chemosensor.     

Polarized fluorescence excitation spectra of adenines

Polarized fluorescence excitation spectra of adenine and N⁶,N⁶-dimethyladenosine, in glassy ethanol solution at 77 K, reveal the existence of the third weak ππ^* transition at about 220 nm, which has been expccted theoretically, but not so far confirmed experimentally. Relative directions between ππ^* transition moments are discussed.     

Procedure for background estimation in energy-dispersive X-ray fluorescence spectra

A method for semi-automatic background estimation in energy-dispersive x-ray fluorescence spectra is outlined. Two cubic splines were investigated and the spline called the Butland interpolant was chosen for further investigation. Prior to the calculation of the spline, peak regions are set up, and suitable knots are defined outside the peak regions. To set up the peak regions, an automatic peak-search routine and a calibration equation are used. For a given peak, the latter relates the full width at half maximum (FWHM) to the peak centre. In turn, the size of the peak regions are defined by the FWHM multiplied by a constant given by the user. The method was tested on several types of spectra. It was found that the optimal size of the peak region decreased with increasing peak density. Reproducibility tests showed that the standard deviation of the summation of counts within a peak region and after background subtraction was less than would be expected from the counting statistics.     

Frequency-domain fluorescence spectroscopy, a new method for the resolution of complex fluorescence emission

The fluorescence emission from complex chemical and biological samples can be resolved by measuring the frequency-response of the emission, which is now possible from 1 to 2000 MHz. The frequency-response allows determination of the components in a mixture, construction of time-resolved emission spectra, and measurement of the dynamic and hydrodynamic properties of biological macromolecules. The instrumentation is relatively simple, and data acquisition times can be short. At present, this method may be superior to direct measurements of time-resolved fluorescence emission.