Absorption and fluorescence spectra

Figure 9.17 Absorption and fluorescence spectra of rhodamine B in methanol (5 X 10 mol 1 ). The curve marked is for the J 2 absorption (process 8 in Figure 9.18) and that marked 5 for process 1. (Reproduced, with permission, from Dienes, A. and Shank, C. Y, Chapter 4 in Creation and Detection of the Excited State (Ed. W. R. Ware), Vol. 2, p. 154, Marcel Dekker, New York, 1972)...

Absorption and Fluorescence Spectra. The absorption spectra of actinide and lanthanide ions in aqueous solution and in crystalline form contain narrow bands in the visible, near-ultraviolet, and near-infrared regions of the spectmm (13,14,17,24). Much evidence indicates that these bands arise from electronic transitions within the and bf shells in which the Af and hf configurations are preserved in the upper and lower states for a particular ion. 

The preceding empirical measures have taken chemical reactions as model processes. Now we consider a different class of model process, namely, a transition from one energy level to another within a molecule. The various forms of spectroscopy allow us to observe these transitions thus, electronic transitions give rise to ultraviolet—visible absorption spectra and fluorescence spectra. Because of solute-solvent interactions, the electronic energy levels of a solute are influenced by the solvent in which it is dissolved therefore, the absorption and fluorescence spectra contain information about the solute-solvent interactions. A change in electronic absorption spectrum caused by a change in the solvent is called solvatochromism. 

Figure 6-8. b- and c-polaii/ed absorption and fluorescence spectra in the range betweeu 18000 cm" and 19000 cm 1. The fluorescence peaks A and C correspond lo tile false origins O and O" identified in absorption. 

Raman spectra of S2 in its triplet ground state have been recorded both in sulfur vapor and after matrix isolation using various noble gases. The stretching mode was observed at 715 cm in the gas phase [46], and at 716 cm in an argon matrix [71]. From UV absorption and fluorescence spectra of sulfur vapor the harmonic fundamental mode of the S2 ground state was derived as t e = 726 cm . The value corrected for anharmonicity is 720 cm [26, 27]. Earlier reports on the infrared absorption spectrum of 2 in matrix isolated sulfur vapor [72] are in error the observed bands at 660, 668 and 680 cm are due to S4 [17] and other species [73]. 

Figure 1. Absorption and fluorescence spectra of the cyanobenz-[f]isoindole chromophore CBI-Ala.

The absorption and fluorescence spectra of a neat film made of RdB-den-drimer are shown in Fig. 2. The absorption spectrum in visible-wavelength region was similar to that obtained from a solution of RdB with a concentration less than 0.1 mmol/1. Interpretation of the fluorescence in terms of the Frank-Condon mechanism indicated that the core RdB chromophore behaved with a site-isolation effect and had little interaction with the neighboring chro-... 

The formation of SWNT/MEHPPV composites was confirmed by absorption and fluorescence spectra. The DMF solution of SWNT/MEHPPV composites or the aqueous solution of the shortened SWNTs was then dropped onto a mica or glass plate. The magnetic processing of the composites or the SWNTs was carried out by using a superconducting magnet (8T) in the horizontal direction, as described below. 

Figure 28 (unbroken line) shows the absorption and fluorescence spectra of colloidal ZnO in aqueous solution at pH = 11.7 The weak fluorescence band at wavelengths close to the onset of absorption was attributed to the fluorescence of the... 

Improta R, Barone V (2004) Absorption and fluorescence spectra of uracil in the gas phase and in aqueous solution a TDDFT quantum mechanical study. J Am Chem Soc 126 14320... 

Figure 6.18. Absorption and fluorescence spectra of l,r-diethyl-2,2 -cyanine bromide at 298 and 77°K. Fluorescence excitation at 498 nm and 565 nm, as indicated by arrows/941 Reprinted by permission of Chemical Physics Letters.

Typical absorption and fluorescence spectra are shown in Figure 11.3. Since energy is lost in the activated state (S ) before fluorescence, the emission maximum always occurs at a lower wavenumber than the absorption maximum. The difference, which is termed the Stokes shift, can be calculated approximately from the absorption spectrum using the Pestemer rule [17,18]. This rule states that the Stokes shift is 2.5 times the half-bandwidth at the absorption maximum. 

In most cases, the linear absorption is measured with standard spectrometers, and the fluorescence properties are obtained with commercially available spectrofluo-rometers using reference samples with well-known <1>F for calibration of the fluorescence quantum yield. In the ultraviolet and visible range, there are many well-known fluorescence quantum yield standards. Anthracene in ethanol (Cresyl Violet in methanol (commonly used reference samples for wavelengths of 350-650 nm. For wavelengths longer than 650 nm, there is a lack of fluorescence references. Recently, a photochemically stable, D-ji-D polymethine molecule has been proposed as a fluorescence standard near 800 nm [57]. This molecule, PD 2631 (chemical structure shown in Fig. 5) in ethanol, has linear absorption and fluorescence spectra of the reference PD 2631 in ethanol to... 

Linear absorption and fluorescence spectra for the series of symmetrical cationic polymethines with 5-butyl-7,8-dihydrobenzo[ /]furo 2,3 /lindolium terminal groups are shown in Fig. 14 for solvents of different polarity. It is known that the polarity of solvents can be characterized by their orientational polarizability, which is given by Af = (e- l)/(2e + 1) — (n2 - l )/(2n2 +1), where e is the static dielectric constant and n is the refractive index of the solvent [41], Calculated A/values... 

Additionally, note that the polarity of the solvent significantly affects not only the positions of absorption and fluorescence spectra but also the fluorescence quantum yields. The largest difference in quantum yield is observed for G19 (eight times larger in toluene) [86]. The effect of solvent polarity on quantum yield and fluorescence lifetime was investigated in mixtures of toluene and ACN (polarity range 0.013-0.306). Polarity dependent quantum yield and lifetime measurements are presented in Fig. 22. 

More advanced scale was proposed by Kamlet and Taft [52], This phenomenological approach is very universal as may be successfully applied to the positions and intensities of maximal absorption in IR, NMR (nuclear magnetic resonance), ESR (electron spin resonance), and UV-VS absorption and fluorescence spectra, and to many other physical or chemical parameters (reaction rates, equilibrium constant, etc.). The scale is quite simple and may be presented as ... 

Figure 7 shows the positions of FL absorption and fluorescence spectra (in centimeter-1) as a function of %. As it is seen, the graphs for different neutral solvents show linear dependence, whereas for protic solvents (alcohols), a different line can be drawn. Such graphs can be practically used for the determination of n in different samples and solvents. If the measured value will be placed on the line for alcohols, this means that the site of our probe incorporation possesses proton donor property. 

Of course, there are some uncertainties in this procedure, as the Onsager model describes the structures of solution and a solute only approximately. It can be noted that there is a good opportunity to calculate dipole moments, exactly, their ratio, in the simpler way using the relative shifts of absorption, and fluorescence spectra. As follows from (16) and (17), dividing them by proper parts we may obtain the following relation ... 

Seliskar C, Brand L (1971) Electronic spectra of 2-aminonaphthalene-6-sulfonate and related molecules. II. Effects of solvent medium on the absorption and fluorescence spectra. JACS 93 5414-5420... 

Fig. 18 Static absorption and fluorescence spectra of 4 -/V,/V-dicthylamino-3-hydroxyflavone in (a) cyclohexane, (b) benzene, (c) dichloromethane, and (d) acetonitrile at 298 K (reprint from ref. [136], Copyright 2005 American Chemical Society)...

The evidence for flavin involvement as deduced from action, absorption, and fluorescence spectra, as well as via non-spectroscopic methods, is then evaluated. It is concluded that all experimental results indirectly support the flavin hypothesis, but that direct proof will have to await the isolation and in vitro characterization of the chromophore. 

Studies of the energetics and dynamics of Cu2 and Ag2 in rare gas solids have also been completed (31,34). The absorption and fluorescence spectra are similarly indicative of strong guest-host interactions in the low lying states of Cu2 and Ag2 Rather than presenting the spectroscopic and photolytic details, a summary of the observed radiative relaxation processes of visible and uv excited Cu2 and Ag2 in rare gas solids is shown below ... 

The absorption and fluorescence spectra of Ag2 in rare gas solids are also clearly indicative of strong guest-host interactions involving the A1 and C1 Instates of Ag2 as summarized below ... 

In 1888, Walter studied the quenching of fluorescence, by the concentration effect, of fluorescein solutions. Nicols and Merrit observed in 1907, in solutions of eosine and resoruflne, the symmetry existing between their absorption and fluorescence spectra. In 1910, Ley and Engelhardt determined the fluorescence quantum yield of various benzene derivatives, values that were still referred to until recent years [18], The works by Lehmann and Wood, around 1910, marked the beginning of analysis based on fluorescence [4],... 

The molecular orientation and interactions of redox chromophores are very important in controlling photoresponses at the molecular level. Absorption and fluorescence spectra will give important information on them. We have studied, photoresponses, specific interactions, in-plane and out-of-plane orientation of various chomophores in LB films composed of amphiphiles shown in Figure 1 [3-12]. 

Actin, role in heart excitation and contraction coupling, 5 81 Actinide carbides, 4 689 Actinide carbonate, 25 430-431 Actinide-gallium compounds, 22 355 Actinide oxides, 24 761 Actinide peroxides, 28 410 Actinides, 23 569. See also Actinides and transactinides Actinide series absorption and fluorescence spectra, 2 490... 

Both FMOC and its hydrolysis products have similar absorption and fluorescence spectra to FMOC-amino acids. Excess FMOC remaining after derivatization reacts with water to form 9-fluorenylmethyl alcohol (FMOC-OH), and if this is not removed prior to sample injection, it elutes as a large, broad peak in the vicinity of proline. 

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