Excitation and emission spectra

Figures 3a-f show the emission and excitation spectra for all six humic fractions. The excitation and emission maxima are listed in Table III along with the maxima of the phase-resolved emission spectra. In each case the emission spectrum was scanned with the excitation maximum wavelength held constant, and the excitation spectrum was scanned with the emission maximum wavelength held constant. Several interesting features are noted. The two humic samples ( Figures 3a,b) each have two excitation maxima and it appears that a double peak has been merged into the emission scan as evidenced by the shoulder on the high energy side of the emission peak. Similarly it seems evident that the exaggerated shoulders in the emission spectra of all the fractions point to the inclusion of two emission peaks in each spectrum. This evidence suggests the presence of two chromophores in each humic fraction.

Figure 5.11 Emission and excitation spectra of [Au3(p-dpmp)2] (SCN)3 in degassed acetonitrile at room temperature. Reproduced with permission from [38]. Copyright (1993) Royal Society of Chemistry.

Fig. 15. Emission and excitation spectra of [Cu(PPli2CH3) dmp] at 4.2 and 300 K (from PA Breddels, thesis, Utrecht, 1983)...

The emission spectrum has been reported only for l.41 A plot of the absorption, emission, and excitation spectra for 1 is shown in Fig. 1. 

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]. 

Fig. 5 Fluorescence emission and excitation spectra of AvGFP at 293K, 0.5 pM in 10 mM Tris...

Quantum-chemical calculations were carried out and correlated with experimental observations concerning the electronic absorption, emission, and excitation spectra of (5-phenyl-l,3,4-oxadiazol-2-yl)-7-hydroxycoumarin 15 <2000SAA1773>. 

Van Duuren [37] examined the use of emission and excitation spectra in the identification of aromatic hyorocarbons. Contour diagrams of fluorescence activity at various excitation and emission wavelengths have been used as a means of identifying petroleum residues. 

Figure 24 shows as an example the gas-phase emission and excitation spectra of the radical cation of dimethyldiacetylene from the work of Maier and coworkers222 and Miller and Bondybey223 who have pioneered these methods. For direct comparison, the bottom part of Figure 24 represents the same spectra taken in neon matrices223 (see below). 

Emission and excitation spectra are recorded using a spectrofluorometer (see Chapter 6). The light source is a lamp emitting a constant photon flow, i.e. a constant amount of photons per unit time, whatever their energy. Let us denote by N0 the constant amount of incident photons entering, during a given time, a unit... 

Emission and excitation spectra were defined in Chapter 3 using the following expression for the measured fluorescence intensity... 

The exceptionally broad range of pH response (from 1 to 8) can be explained by the existence of two consecutive transitions neutral form-monoanion and monoanion-dianion. The pH dependence of the emission and excitation spectra is shown in Figure 10.5. 

Fig. 10.5. Various forms of fluorescein in aqueous solution and pH dependence of its emission and excitation spectra. The emission spectra are normalized to the same height at the maximum (spectra from Slavik, 1994).

Chapter 3 is devoted to the characteristics of fluorescence emission. Special attention is paid to the different ways of de-excitation of an excited molecule, with emphasis on the time-scales relevant to the photophysical processes - but without considering, at this stage, the possible interactions with other molecules in the excited state. Then, the characteristics of fluorescence (fluorescence quantum yield, lifetime, emission and excitation spectra, Stokes shift) are defined. 

Figure 8.2. Fluorescence emission and excitation spectra of a strongly scattering sample as detected in forward (Ff) and backward (Fb) direction. (Pyrene adsorbed on silica gel, surface loading cpyr = 5.5-10-7 mol g l, spec, surface area cisiiica = 500 m2 g ),...

Emission and excitation spectra were obtained for both natural and protease-liberated flavoprotein materials in 100 mM acetic acid. The Xmax for excitation was 330 for the natural and 410 nm for the protease-liberated flavoprotein while that for emission were 420 and 480 nm, respectively. These spectroscopic data show that these are flavoproteins and that the protein composition of natural and protease-liberated flavoprotein are somehow different. 

Spectroscopic properties of [Ru(bpy)3] " ", and the effects of varying the diimine ligands in [Ru(bpy)3 L ] + (L = diimine) on the electronic spectra and redox properties of these complexes have been reviewed. The properties of the optical emission and excitation spectra of [Ru(bpy)3] +, [Ru(bpy)2(bpy-d )] + and [Ru(bpy-d )3] " " and of related Os, Rh , and Pt and Os species have been analyzed and trends arising from changes in the metal d or MLCT character in the lowest triplet states have been discussed. A study of the interligand electron transfer and transition state dynamics in [Ru(bpy)3] " " has been carried out. The results of X-ray excited optical luminescence and XANES studies on a fine powder film of [Ru(bpy)3][C104]2 show that C and Ru localized excitation enhances the photoluminescence yield, but that of N does not. 

Fig. 5.56. Emission and excitation spectra of calcium halophosphates A-Sb emission B-Mn emission C-warm-white halophosphate (Blasse and Grabmaier 1994)...

Steady-state emission and excitation spectra are measured for the dimethyl terephthalate and three polyesters in four solvents. The polymers have the repeating unit ABm, where A is -CO— C6H4— COO-, B is -(CH2—CH2—0)m- and m - 1,2,3. An RIS treatment of the unperturbed polymers identifies the conformations that should be conducive to excimer formation by nearest-neighbor aromatic rings. The population of such conformations is maximal in the polyesters in which m = 2. 

Emission characteristics of a molecular system can be expressed by three types of measurements (1) observation of emission and excitation spectra, (2) measurement of quantum efficiencies, and (3) determination of decay constants or radiative lifetimes. 

When irradiated at 360 nm, [Eu(terpy)3]3+ fluoresces at 595 nm while [Tb(terpy)]3+ fluoresces at 540 nm the other species do not fluoresce and hence the reaction kinetics could be followed by measurement of fluorescence intensity giving k = 1.9 x 10-3 s 1. The reaction was first order in [Eu(terpy)3]3+ and zero order in Tb, proceeding as shown in equations (3) and (4). The rapid nature of the second step was confirmed directly in separate experiments by similar means. Dye-laser excited emission and excitation spectra of [Eu(terpy)3](004)3 in the solid state and in acetonitrile solution have been measured168 and evidence has been obtained which was interpreted as pointing towards the presence of some mono- or bi-dentate terpyridyl ligands in addition to those which are tridentate as observed in the X-ray structural determination. 

Phosphorescence. Phosphorescence of Fe3+-doped Gels. In H20. In all systems studied the phosphorescence of the initial Fe3+-doped gel showed a wreak emission at 690 nm with a shoulder at ca. 720 nm. Emission and excitation spectra were similar to those shown in Figure 1. The phosphorescence comes from the Ai - 47 transition while the various other transitions in the Fe3+ ion in tetrahedral coordination are apparent in the excitation spectrum (8, 10). Throughout the induction period emission intensity increased only slightly, the peak at 690 nm increasing somewhat more than the shoulder at 720 nm. After induction the signal rose rapidly until a constant intensity was attained. The rapid increase in intensity of the phosphorescence signal after induction ended paralleled the intensity increase of the x-ray diffraction lines. 

Figure 23-13 (A) Corrected emission and excitation spectra of riboflavin tetrabutyrate in w-heptane. Concentration, about 0.4 mg I-1. Curve 1 excitation spectrum emission at 525 nm. Curve 2 emission spectrum excitation at 345 nm. FromKotaki and Yagi.128 (B) Indole in cyclohexane, T = 196 K. 1, Fluorescence excitation spectrum 2, fluorescence spectrum and 3, phosphorescence spectrum. From Konev.125...

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