Spectra fluorescence

Fluorescence Spectra.—Broad u.v. emission from magnesium atoms in argon and krypton matrices at 4.2 and 12 K, respectively, has been observed at 297.0 and 

respectively. The band is due to the - S excitation of the atom, but the nature of the emitting species was not positively identified.305 There have been several studies on the emission systems of helium, neon, argon, and xenon.300 Emission intensities of OH u.v. bands 307 and u.v. spectra of CH+ and OD+,308 transition moments of CH in emission,309 a re-examination of the vacuum-u.v. emission spectrum of CO in the 95—120 nm region310 which shows that many bands assigned previously to CO arise from N2, the SO B3S - 3S band system,311 vacuum-u.v. emission from electronically excited N2,312 fluorescence from molecular iodine 109 195 19°-313 and diatomic halogen fluorides,110 fluorescence from the C22+ state of NS,314 Cd2 fluorescence (phosphorescence) due to the 3HU+ - 1S + transition,316 photoluminescence from Rb2 310 and RuO,317 the ytterbium vapour gas laser,318 and laser-stimulated fluorescence of diamond319 have been the subjects of recent papers. 

The fluorescence of N02 excited by the He-Cd 442 nm laser exhibits characteristics of perpendicular transitions belonging to 2B1(K 0) vibronic states.320 Near-i.r. emission from HOa arising from both vibrational ground-state overtone transitions and vibronic 2A - 2A transitions has been observed,321 and 02 803 

Of the many papers on the fluorescence spectral properties of complex polyatomic molecules published during the past year, a few may be singled out as meriting special attention. There have been several additions to the growing list of molecules exhibiting relatively easily observable fluorescence from second excited singlet states. The observations this year have been largely confined to 

Hirayama and Lipsky have extended their observations of weak fluorescence from unlikely candidates for luminescence by examining propylene, 1-butene, -2-butene, fra -2-butene, 1-hexene, -2-hexene, tra/z.s-2-hexene, 2-methyl-pentene, and 2,3-dimethyl-2-butene excited at 184.9 nm in the vapour and liquid phases.328 Quantum yields in general were of the order of 10-8, and fluorescence observed was in the 35 000—50 000 cm-1 region of the spectrum. The authors 

The excited molecules release their energy either by spontaneous or induced emission or by collisional deactivation (Fig. 2.20). The spatial distribution of spontaneous emission depends on the orientation of the excited molecules and on the symmetry properties of the excited state Ej. If the molecules are randomly oriented, the spontaneous emission (often called fluorescence) is isotropic. 

The fluorescence spectrum (emission spectrum) emitted from a discrete upper level Ek consists of discrete lines if the terminating lower levels Ei are bound states. A continuum is emitted if Ei belongs to a repulsive state of a molecule that dissociates. As an example, the fluorescence spectrum of the EI transition of the NaK molecule is shown in Fig. 2.21. It is emitted from a selectively excited bound vibrational level of the 77 state that has been populated by optical pumping with an argon laser. The fluorescence terminates into a repulsive state, which has a shallow van der Waals minimum. Transitions terminating to energies Ek above the dissociation energy form the continuous part of the spectrum, whereas transitions to lower bound levels in the van der Waals potential well produce discrete lines. The modulation of the continuum reflects the modulation of the transmission probability due to the maxima and nodes of the vibrational wave function V vib( ) in the upper bound level [54]. 

After the sample s absorption spectrum has been measured, one can select an excitation wavelength, X x. that falls within the absorption envelope. There will be other Actors that may influence the selection of Xex- If the sample is homogeneous and contains a single molecular chromophore, then any wavelength may be appropriate. In the case of samples that contain more than a single molecular chromophore, such as in a protein (vide infra), then the choice of Xex will depend on whether preferential excitation of one of those chromophores is desired. 

An important parameter of the sample that must be considered is the absorbance of the sample at Xex- Equation 8 shows that the rate of fluorescence emission. Ip, is determined by the rate of light absorbance. In dilute solution equation 8 can be expanded in terms of a series and where scl is small then it can be approximated that  

This approximation can lead to an error known as the inner filter effea. The solution at the front of the cell is exposed to a higher excitation light intensity 

Hgure 8 A demonstration of the overlap of excitation and emission monochromator bandpass when and Xem are close to one another thus explaining the observation of Rayleigh scattering of Xex- 

It is always necessary to record a solvent/bufSer blank under identical instrumental conditions. This can be subsequentfy subtracted from the sample fluorescence spectrum for quantitative purposes. 

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Murakami H, Kinoshita S, Hirata Y, Okada T and Mataga N 1992 Transient hole-burning and time-resolved fluorescence spectra of dye molecules in solution evidence for ground-state relaxation and hole-filling effect J. Chem. Phys. 97 7881-8... 

Sun Y-P, Wang P and Hamilton N B 1993 Fluorescence spectra and quantum yields of Buckminsterfullerene (Cgg) in room-temperature solutions. No excitation wavelength dependence J. Am. Chem. Soc. 115 6378-81... 

Tunable visible and ultraviolet lasers were available well before tunable infrared and far-infrared lasers. There are many complexes that contain monomers with visible and near-UV spectra. The earliest experiments to give detailed dynamical infonnation on complexes were in fact those of Smalley et al [22], who observed laser-induced fluorescence (LIF) spectra of He-l2 complexes. They excited the complex in the I2 B <—A band, and were able to produce excited-state complexes containing 5-state I2 in a wide range of vibrational states. From line w idths and dispersed fluorescence spectra, they were able to study the rates and pathways of dissociation. Such work was subsequently extended to many other systems, including the rare gas-Cl2 systems, and has given quite detailed infonnation on potential energy surfaces [231. 

Figure Cl.5.9. Vibrationally resolved dispersed fluorescence spectra of two different single molecules of terrylene in polyetliylene. The excitation wavelengtli for each molecule is indicated and tlie spectra are plotted as the difference between excitation and emitted wavenumber. Each molecule s spectmm was recorded on a CCD detector at two different settings of tire spectrograph grating to examine two different regions of tlie emission spectmm. Type 1 and type 2 spectra were tentatively attributed to terrylene molecules in very different local environments, although tlie possibility tliat type 2 spectra arise from a chemical impurity could not be mled out. Furtlier details are given in Tchenio [105-1071.

Figure Cl.5.11. Far-field fluorescence images (A and D), corresponding fluorescence spectra (B and E), and fluorescence decays (C and F) for two different molecules of a carbocyanine dye at a PMMA-air interface.

Tchenio P, Myers A B and Moerner W E 1993 Dispersed fluorescence spectra of single molecules of pentacene in p-terphenyl J. Chem. Phys. 97 2491-3... 

Fleury L, Tamarat P, Lounis B, Bernard J and Orrit M 1995 Fluorescence spectra of single pentacene molecules in p-terphenyl at 1.7 K Chem. Phys. Lett. 236 87-95... 

The sensitivities of particular spectroscopic teclmiques to specific chemical features are described more fully in tire next section. Perhaps tire most common and versatile probes of reaction dynamics are time-resolved UV-vis absorjDtion and fluorescence measurements. Wlren molecules contain cliromophores which change tlieir stmcture directly or experience a change of environment during a reaction, changes in absorjDtion or fluorescence spectra can be expected and may be used to monitor tire reaction dynamics. Altliough absorjDtion measurements are less sensitive tlian fluorescence measurements, tliey are more versatile in tliat one need not rely on a substantial fluorescence yield for tire reactants, products or intennediates to be studied. 

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)...

Figure 9.33 Single vibronic level fluorescence spectra obtained by collision-lree emission Irom the zero-point level of the state of (a) pyrazine and (b) perdeuteropyrazine. (Reproduced, with permission, Ifom Udagawa, Y., Ito, M. and Suzuka, I., Chem. Phys., 46, 237, 1980)...

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. 

X-Ray Spectrometers. An x-ray spectrometer is an instmment that measures the fluorescence spectra of samples. The associated computer software then determines the quaUtative and quantitative elemental composition of the samples from the resulting spectra. 

Principal component analysis has been used in combination with spectroscopy in other types of multicomponent analyses. For example, compatible and incompatible blends of polyphenzlene oxides and polystyrene were distinguished using Fourier-transform-infrared spectra (59). Raman spectra of sulfuric acid/water mixtures were used in conjunction with principal component analysis to identify different ions, compositions, and hydrates (60). The identity and number of species present in binary and tertiary mixtures of polycycHc aromatic hydrocarbons were deterrnined using fluorescence spectra (61). 

Coumarin, 7-amino-7-(diethylamino)-, I, 333 Coumarin, 7-amino-4-methyl-fluorescence spectra, 3, 601 Coumarin, 7-amino-3-phenyl-brightening agents, I, 339 Coumarin, 4-aryl-occurrence, 3, 677 synthesis, 3, 810 Coumarin, 3-arylazo-4-hydroxy-structure, 3, 643 Coumarin, 3-bromo-reactions... 

Diels-Alder reactions, 4, 842 flash vapour phase pyrolysis, 4, 846 reactions with 6-dimethylaminofuKenov, 4, 844 reactions with JV,n-diphenylnitrone, 4, 841 reactions with mesitonitrile oxide, 4, 841 structure, 4, 715, 725 synthesis, 4, 725, 767-769, 930 theoretical methods, 4, 3 tricarbonyl iron complexes, 4, 847 dipole moments, 4, 716 n-directing effect, 4, 44 2,5-disubstituted synthesis, 4, 116-117 from l,3-dithiolylium-4-olates, 6, 826 electrocyclization, 4, 748-750 electron bombardment, 4, 739 electronic deformation, 4, 722-723 electronic structure, 4, 715 electrophilic substitution, 4, 43, 44, 717-719, 751 directing effects, 4, 752-753 fluorescence spectra, 4, 735-736 fluorinated derivatives, 4, 679 H NMR, 4, 731 Friedel-Crafts acylation, 4, 777 with fused six-membered heterocyclic rings, 4, 973-1036 fused small rings structure, 4, 720-721 gas phase UV spectrum, 4, 734 H NMR, 4, 7, 728-731, 939 solvent effects, 4, 730 substituent constants, 4, 731 halo... 

Fluorescence spectra were measured at wavelength scanning of tunable dye-laser. In spite of the monochromic excitation the fluorescence spectmm has quite complex composition. Such variety of wavelengths allows to optimize fluorescence excitation and registration for any technological conditions. 

When recording excitation and fluorescence spectra it must be ensured that monochromatic light falls on the detector This can best be verified in instruments built up on the kit principle or in those equipped with two monochromators (spectrofluonmeters) The majority of scanners commercially available at the moment do not allow of such an optical train, which was realized in the KM3 chromatogram spectrometer (Zeiss) So such units are not able to generate direct absorption or fluorescence spectra for the charactenzation of fluorescent components... 

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. 

If the ultraviolet spectra of a potentially tautomeric compound and of both alkylated derivatives are too similar to allow conclusions to be drawn regarding their structures, sometimes fluorescence spectra can be used instead. By using this technique, Gompper and Her-linger showed that 4,5-diphenyloxazol-2-one (53) does, indeed, exist in the 2-oxo form. 

Fischer and Neumann have discussed the ultraviolet and fluorescence spectra of 199 and 200 and consider them to support the polyoxo forms shown. 

Absorption and emission spectra of six 2-substituted imidazo[4,5-/]quinolines (R = H, Me, CH2Ph, Ph, 2-Py, R = H CH2Ph, R = Ph) were studied in various solvents. These studies revealed a solvent-independent, substituent-dependent character of the title compounds. They also exhibited bathochromic shifts in acidic and basic solutions. The phenyl group in the 2-position is in complete conjugation with the imidazoquinoline moiety. The fluorescence spectra of the compounds exhibited a solvent dependency, and, on changing to polar solvents, bathochromic shifts occur. Anomalous bathochromic shifts in water, acidic solution, and a new emission band in methanol are attributed to the protonated imidazoquinoline in the excited state. Basic solutions quench fluorescence (87IJC187). 

The association of the excited state derived from four 2-substituted imidazo [4,5-/]quinolines with 2-propanol in cyclohexane has been studied. The unusual bathochromic shift and the bandwidth of the fluorescence spectra of these heterocyclic compounds in 2-propanol-cyclohexane solutions, compared with those... 

The similarity of the ultraviolet spectrum of 4,5-diphenyloxazol-2-one (91) with those of both alternative methyl derivatives preclude application of the spectral comparison method to the elucidation of their structures, but the fluorescence spectra of these compounds indicate that 91 exists in the oxo form. ° Infrared data for a number of substituted oxazol-2-ones support this conclusion. ... 

Eu(III) complexes of quinolinecarboxylic acids, including 5, were studied (00MI31). Those of complexes of 5 with Eu(III) and Tb(III) ion were studied, and they were applied for analysis of 5 in medicinal preparations (00UKZ115). Stability of lanthanide complexes with 5 was studied (00MI67). The fluorescence spectra of 5 complexed with Co(II) and ATP was measured (01SA(A)1317). 

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