Excitation spectra species

More fluorescence features than just the emission intensity can be used to develop luminescent optosensors with enhanced selectivity and longer operational lifetime. The wavelength dependence of the luminescence (emission spectmm) and of the luminophore absorption (excitation spectrum) is a source of specificity. For instance, the excitation-emission matrix has shown to be a powerful tool to analyze complex mixtures of fluorescent species and fiber-optic devices for in-situ measurements (e.g. 

Figure 10 Chemiluminescence spectrum of S2 observed in the selective reaction of OCIO with H2S. Note that this is the same excited-state species observed by the FPD. (Reprinted with permission from Ref. 81. Copyright 1982 American Chemical Society.)...

In methanol/DMSO solvent mixtures the fluorescence spectrum of TIN (A.max = 400 nm) displays a normal Stokes shift indicating that this emission arises from a non proton-transferred, excited state of TIN. The fluorescence excitation spectrum for this emission coincides with the absorption spectrum of the resolved non-planar species suggesting that this conformer is the ground-state precursor responsible for the observed emission. As the amount of DMSO in the mixture increases the fluorescence maximum undergoes a bathochromic shift from 415 nm in pure methanol to 440 nm in pure DMSO. 

The values of ftot for various benzotriazole compounds in a range of solvents are listed in Table II. Values of the fluorescence quantum yield for TIN and TINS, corrected for the absorbance by their non-fluorescent, planar conformers at the excitation wavelength, are listed in Table III. In all the benzotriazole solutions examined, maximum fluorescence emission was observed at about 400 nm indicating that this emission originates from the non proton-transferred species. This was confirmed by examination of the fluorescence excitation spectrum which corresponds to the absorption spectrum of the non-planar form of the molecule. 

In multicomponent systems A"0 can be written as a sum of the individual absorption coefficients A ot = 2TA , where each AT,(A ) depends in a different way on the wavelength. If one or more of the components are fluorescent, their excitation spectra are mutually attenuated by absorption filters of the other compounds. This effect is included in Eqs. (8.27) and (8.28) so that examples like that of Figure 8.4 can be quantified. The two fluorescent components are monomeric an aggregated pyrene, Mi and Mn. The fluorescence spectra of these species are clearly different from each other but the absorption spectra overlap strongly. Thus the excitation spectrum of the minority component M is totally distorted by the Mi filter (absorption maxima of Mi appear as a minima in the excitation spectrum ofM see Figure 8.4, top). In transparent samples this effect can be reduced by dilution. However, this method is not very efficient in scattering media as can be seen by solving Eqs. (8.27 and 8.28) for bSd — 0. Only the limit d 0 will produce the desired relation where fluorescence intensity and absorption coefficient of the fluorophore are linearly proportional to each other in a multicomponent system. 

In contrast with previous studies on He2Cl2 cluster, in the present work localized structures are determined for the lower He2Br2 vdW states. Traditional models based on a He2Cl2 tetrahedron frozen stucture have failed to reproduce the experimental absorption spectrum, suggesting a quite delocalized structure for its vibrationally ground state. Here, based on ab initio calculations we propose different structural models, like linear or police-nightstick , in order to fit the rotationally resolved excitation spectrum of He2Cl2 or similar species. 

The complex is luminescent in the solid state and in solution in pyridine. The absorption spectrum shows a maximum at 340 nm and the emission spectrum displays a band at 425 nm. The crystals are also luminescent, but the excitation and emission spectra appear at different wavelengths. Thus, the complex emits at 490 nm and the excitation spectrum is complicated, with bands in a wide range from 300 to 450 nm. This result suggests that different species are responsible for luminescence in the solid state and in solution, with the isolated trinuclear complex being the emitting species in solution, while the luminescent properties of the crystal are the result of the extended supramolecular aggregation in the solid. As before, the complex did not exhibit solvoluminescence. 

With this method, we have shown [27] that the two main bands of the excitation spectrum recorded at naphthol-(NH3)2+ mass peak do not belong to the same species one band excitation leads to a narrow mass peak and thus corresponds to the direct excitation of 1 -2 complex, since the other one leads to a broad peak and corresponds to the excitation of the 1 -3 complex, which looses one ammonia molecule in the ionic state. 

Figure 4b shows the measured transient difference absorption spectrum as a function of the x-ray probe energy E, recorded 50 ps after laser excitation (data points with error bars) for a sample containing 80 mmol/1 solution of [Ru"(bpy)3]2+ in H2O. This transient contains all the electronic changes from the reactant state absorption spectrum, R E), to the product state absorption spectrum, P(E,t), at the time t after photoexcitation. WithXO being the fraction of excited state species at time t, the transient absorption spectrum T(E,t) is given by... 

By examining the excitation spectrum of a molecular species one can deduce a ground state Boltzmann temperature. Also, as will be discussed below, if one can predict the population distribution in the atom or molecule under excitation conditions, then one can use the observed fluorescence spectrum to recover the gas temperature. 

When calcination was performed at 470°C, the sample turns light yellow, indicating the conversion of intermediates probably into oxides and other species, accompanied by further V migration to the gel (Fig. 11c). Luminescence measurements from our laboratory (33) have shown that calcination at 470°C results in complete disappearance of vanadyl porphyrin peaks and appearance of some new excitation peaks which can not be observed in the corresponding excitation spectrum of the EuYV(p)AAAC sample. These data suggest that intermediates exist after calcination and that these species may play a critical role during V migration. 

A) shows an intense and narrow absorption at 340 nm and the excitation spectrum shows a maximum at 340 nm associated with a broad emission centred around 544 nm (Figure 3A, F). At this level of exchange, Uytterhoeven s crystallographic results (3) indicate the probable presence of a charged cluster Ag29+ arising from the simultaneous occupancy (at least to a certain extent, measured by the excess of population in site I ) of one site I and one adjacent site I by a silver ion. Therefore, we associate the species giving rise to these optical spectra with the cluster Ag2spectroscopic properties of which will be described in a later section (where q is shown to be unity). 

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