Fluorescence excitation spectra and

Fig. 7.6. Normalized fluorescence excitation spectra and fluorescence (bold lines) spectra of methyl 8-(2-anthroyl)-octanoate in n-hexane, N,N-dimethylformamide and ethanol at 20 °C. The maximum of emission is located at 430, 450 and 485 nm, respectively (excitation wavelength 360 nm) (reproduced with permission from Perochon et al., 1991).

Figure 1. The experimental system used for measuring fluorescence excitation spectra and reaction rate constants...

Fluorescence excitation spectra and fluorescence spectra 300 of jet-cooled azulene, including the Sj, Sj, and S -Sy transitions... 

From the dispersed fluorescence, excitation spectra and their dependence on solvent -concentration we identified the different solvated species and obtained the frequency of the new vibrational modes that result from complexation (typically 170 cm and below). For isoquinoline (IQ) three solvents were used (water, methanol and acetone) to deduce some particular effects regarding the nature of hydrogen bonding in the species ... 

Molecular fluorescence spectroscopy is a commonly employed analytical method that is sensitive to certain chemical properties of FA (9-13). Fulvic acid s molecular fluorescence is principally due to conjugated unsaturated segments and aromatic moieties present in the macromolecule (14). Several types of fluorescence spectra can be measured, including an excitation emission matrix or total luminescence spectrum, constant offset synchronous fluorescence, excitation spectra, and emission spectra, furnishing the researcher with useful data. The ability to resolve and select multiple fluorescent species makes these approaches extremely useful for studying FA relative to its chemical reactivity. 

Ghosh, K., and Schnitzer, M. (1981). Fluorescence excitation spectra and viscosity behavior of a fulvic acid and its copper and iron complexes. Soil Sci. Soc. Am. J. 45, 25 -29. 

Fluorescence and fluorescence excitation spectra, and fluorescence quantum yields of the fullerene clusters are different from those of the fullerene monomers. The excitation and absorption spectra of the fullerene clusters are in good agreement [80]. The observed fluorescence yields of fiillerenes decrease significantly upon the formation of clusters. This is opposite to the trend of increasing transition probabilities as measured by the integrated molar absorptivities. The lower fluorescence yields for the fullerene clusters are likely due to more efficient excited state nonradiative decays. One possible mechanism is the quenching of photoexcited fiillerenes by neighboring fullerene molecules in the clusters with excimer-like interactions [82]. However, no flillerene-fiillerene excimer emissions have been observed. 

Reflectance spectra show four absorption bands centered at about 280, 330, 400 and 450 nm. The two most intense bands, i.e., those at 280 and 330 nm, and that at 450 nm are revealed by the fluorescence excitation spectra and thus characterizes emitting fluorophores present naturally in the flours. 

A detailed study of the predissociation channel (iii) from the C A state in HCN and DCN, which included analysis of the absorption and photofragment fluorescence excitation spectra, and measurements of the relative quantum yields and polarizations of the fluorescence following excitation into different vibronic levels, provides an example of the interrelation between photochemistry and spectroscopyThis was used to help characterise the nature of the excited electronic parent molecular states and provide information on the topography of the potential surfaces over which the predissociation proceeds. The photofragment fluorescence excitation spectra from HCN and DCN are displayed in Figs. 3.4. and 3.4.8 all the major vibronic bands can be attributed to progressions in the C state, and the CN(B - X) fluor-... 

To establish whether a retinoid interacts specifically with the CRBP retinolbinding site, absorption and fluorescence spectra of the retmoid-CRBP complex may be analyzed. We show here that the RME-CRBP complex exhibits spectral characteristics similar to those of retinol-CRBP, like the vibronic fine structures of the absorption and fluorescence excitation spectra and the quite intense fluorescence emission of CRBP-bound RME (Figs. 2 and 3). Absorption and fluorescence spectra of the RME-CRBP complex can be obtained as described below. 

Figure Cl.5.2. Fluorescence excitation spectra (cps = counts per second) of pentacene in /i-teriDhenyl at 1.5 K. (A) Broad scan of the inhomogeneously broadened electronic origin. The spikes are repeatable features each due to a different single molecule. The laser detuning is relative to the line centre at 592.321 nm. (B) Expansion of a 2 GHz region of this scan showing several single molecules. (C) Low-power scan of a single molecule at 592.407 nm showing the lifetime-limited width of 7.8 MHz and a Lorentzian fit. Reprinted with pennission from Moemer [198]. Copyright 1994 American Association for the Advancement of Science.

Figure Cl.5.4. Comparison of near-field and far-field fluorescence images, spectra and lifetimes for the same set of isolated single molecules of a carbocyanine dye at a PMMA-air interface. Note the much higher resolution of the near-field image. The spectmm and lifetime of the molecule indicated with the arrow were recorded with near-field excitation and with far-field excitation at two different excitation powers. Reproduced with pennission from Trautman and Macklin [125].

The polarization properties of single-molecule fluorescence excitation spectra have been explored and utilized to detennine botli tlie molecular transition dipole moment orientation and tlie deptli of single pentacene molecules in a /7-teriDhenyl crystal, taking into account tlie rotation of tlie polarization of tlie excitation light by tlie birefringent... 

Finally, tlie ability to optically address single molecules is enabling some beautiful experiments in quantum optics. The non-Poissonian photon arrival time distributions expected tlieoretically for single molecules have been observed directly, botli antibunching at short times [112] and bunching on longer time scales [6, 112 and 113]. The fluorescence excitation spectra of single molecules bound to spherical microcavities have been examined as a probe... 

Guttler F, Sepiol J, Plakhotnik T, Mitterdorfer A, Renn A and Wild U P 1993 Single molecule spectroscopy fluorescence excitation spectra with polarized light J. Lumin. 56 29-38... 

Figure 9.46 Rotational structure of the Ojj bands in the fluorescence excitation spectra of s-tetrazine dimers at about 552 run. Bottom Ojj band of planar dimer. Middle Ojj band of T-shaped dimer with transition in monomer unit in stem of T. Top Ojj band of T-shaped dimer with transition in monomer unit in top of T. (Reproduced, with permission, from Haynam, C. A., Brumbaugh, D. V and Levy, D. H., J. Chem. Phys., 79, f58f, f983)...

In a skimmed supersonic jet, the parallel nature of the resulting beam opens up the possibility of observing spectra with sub-Doppler resolution in which the line width due to Doppler broadening (see Section 2.3.4) is reduced. This is achieved by observing the specttum in a direction perpendicular to that of the beam. The molecules in the beam have zero velocity in the direction of observation and the Doppler broadening is reduced substantially. Fluorescence excitation spectra can be obtained with sub-Doppler rotational line widths by directing the laser perpendicular to the beam. The Doppler broadening is not removed completely because both the laser beam and the supersonic beam are not quite parallel. 

FIG. 5 Laurdan fluorescence excitation spectra recorded between 250 and 420 nm (emission wavelength, 439 nm) at different times during the acidification and the rennet-induced coagulation kinetics of BLG5 reconstituted milk 35, 70, 125, 175, and 300 min. A.U. = arbitrary units. 

FBAs can also be estimated quantitatively by fluorescence spectroscopy, which is much more sensitive than the ultraviolet method but tends to be prone to error and is less convenient to use. Small quantities of impurities may lead to serious distortions of both emission and excitation spectra. Indeed, a comparison of ultraviolet absorption and fluorescence excitation spectra can yield useful information on the purity of an FBA. Different samples of an analytically pure FBA will show identical absorption and excitation spectra. Nevertheless, an on-line fluorescence spectroscopic method of analysis has been developed for the quantitative estimation of FBAs and other fluorescent additives present on a textile substrate. The procedure was demonstrated by measuring the fluorescence intensity at various excitation wavelengths of moving nylon woven fabrics treated with various concentrations of an FBA and an anionic sizing agent. It is possible to detect remarkably small differences in concentrations of the absorbed materials present [67]. 

The fluorescence and absorption spectra of DTT-A.V-dioxidc 20a with polar covalent bonds was studied in THF, toluene, and decalin. The spectral line and peak energy are almost independent of the solvent polarity. The fluorescence spectra of the decalin and toluene solutions (almost the same polarity) are red-shifted by about 5 nm, with respect to the THF solution of higher polarity. No evident solvatochromism was observed. The absorbance and fluorescence excitation spectra (at the fluorescence peak wavelength) for DTT-3, 3 -dioxide 20a (normalized to peak value) was compared. The fluorescence excitation signal is, in fact, dependent both on the density of the excited state (as the absorbance) and on the efficiency of the relaxation from the excited state of the emitting one <2005PCB6004>. 

Ehrig, T., O Kane, D. J. and Prendergast, F. G. (1995). Green-fluorescent protein mutants with altered fluorescence excitation spectra. FEBS Lett. 367, 163-6. 

Wakeham [14] has discussed the application of synchronous fluorescence spectroscopy to the characterization of indigenous and petroleum derived hydrocarbons in lacustrine sediments. The author reports a comparison, using standard oils, of conventional fluorescence emission spectra and spectra produced by synchronously scanning both excitation and emission monochromators. 

Figure 8.4. Fluorescence excitation spectra of pyrene (sample two of Figure 8.3) measured at A = 392 nm (region of Mi-emission) and J.e = 500 nm (region of A/ -emission) upper panel thick layer (d = 1 cm), lower panel thin layer (single grains).

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