Phosphorescence spectroscop

Accuracy The accuracy of a fluorescence method is generally 1-5% when spectral and chemical interferences are insignificant. Accuracy is limited by the same types of problems affecting other spectroscopic methods. In addition, accuracy is affected by interferences influencing the fluorescent quantum yield. The accuracy of phosphorescence is somewhat greater than that for fluorescence. 

Time, Cost, and Equipment As with other optical spectroscopic methods, fluorescent and phosphorescent methods provide a rapid means of analysis and are capable of automation. Fluorometers are relatively inexpensive, ranging from several... 

Nuclear magnetic resonance spectroscopy is a technique that, based on the magnetic properties of nuclei, reveals information on the position of specific atoms within molecules. Other spectroscopic methods are based on the detection of fluorescence and phosphorescence (forms of light emission due to the selective excitation of atoms by previously absorbed electromagnetic radiation, rather than to the temperature of the emitter) to unveil information about the nature and the relative amount specific atoms in matter. 

Analyses I.r. spectra were measured as smears on sodium chloride plates or as a solution in carbon tetrachloride using a Perkin-Elmer 567 grating spectrophotometer, while u.v. spectra were measured as a solution in hexane (spectroscopic grade) using a Unicam SP 1700 instrument. Fluorescence and phosphorescence spectra were recorded as described elsewhere (5, 6). 

The fractions from elution chromatography were studied by a number of spectroscopic methods, n.m.r., i.r., u.v., fluorescence and phosphorescence spectroscopy. Equivalent fractions from chromatographic separation of the various oils showed no significant differences in their spectra and it appears that the composition of the fractions was independent of the catalyst concentration used to produce the oil. Though, as previously mentioned the amounts of the various fractions especially the polar fractions differ with the catalyst concentration. G.1.C. analysis of the saturate fractions also indicated no changes with different catalyst concentrations. 

The phosphorescence of Pt2 (I OsKHq in aqueous solution is quenched by l,l-bis(2-sulfoethyl)-4,4f-bipyridinium inner salt (BSEP). Transient absorption attributable to BSEP ( nax 610 nn) is observed in flash kinetic spectroscopic studies of aqueous solutions containing Pt2( Os Hq and BSEP, thereby establishing an electron transfer quenching mechanism ... 

It is worth noting some historical aspects in relation to the instrumentation for observing phosphorescence. Harvey describes in his book that pinhole and the prism setup from Newton were used by Zanotti (1748) and Dessaignes (1811) to study inorganic phosphors, and by Priestley (1767) for the observation of electroluminescence [3], None of them were capable of obtaining a spectrum utilizing Newton s apparatus that is, improved instrumentation was required for further spectroscopic developments. Of practical use for the observation of luminescence were the spectroscopes from Willaston (1802) and Frauenhofer (1814) [13]. 

Spectroscopic techniques look at the way photons of light are absorbed quantum mechanically. X-ray photons excite inner-shell electrons, ultra-violet and visible-light photons excite outer-shell (valence) electrons. Infrared photons are less energetic, and induce bond vibrations. Microwaves are less energetic still, and induce molecular rotation. Spectroscopic selection rules are analysed from within the context of optical transitions, including charge-transfer interactions The absorbed photon may be subsequently emitted through one of several different pathways, such as fluorescence or phosphorescence. Other photon emission processes, such as incandescence, are also discussed. 

The phthalocyanines, naphthalocyanines, and certain of their metal derivatives (Figure 6.17) are infrared fluorophores. 61"64 As a class, they are exceptionally stable compounds, with copper (Cu) phthalocyanine (not a fluorophore) remaining intact above 300 °C in air. First used for textile dyeing in the last century and still widely used, there is a rich chemistry of phthalocyanines. Most derivatives can be made by prolonged heating of a phthalimide or phthalic acid derivative with a metal in powder or salt form at elevated temperature. Several derivatives absorb in the near-IR, and either fluoresce or phosphoresce. The electronic transitions of phthalocyanines are complex and have been extensively studied, at least in part because the symmetry of the molecule makes theoretical calculations of its spectroscopic behavior more tractable. Unsubstituted phthalocyanines and naphthalocyanines are, as a class, very insoluble in solvents other than, for instance, nitrobenzene. Sulfonated phthalocyanines are water soluble and exhibit spectra comparable to the parent derivative. Photolumines-cent phthalocyanines (Pcs) include SiPc, ZnPc, and PC itself. These compounds have been little used for practical infrared fluorometry to date however, Diatron Corpora-... 

Spectroscopic data of nitroaromatics have been reviewed D in addition, several papers on luminescence of nitroaromatic compounds have appeared recently. The phosphorescence polarization of several aromatic nitro compounds has been studied and recent triplet-triplet absorption data on 1- and 2-nitro-naphthalene have become available ). 

Ley and Schanze have also examined the luminescence properties of the polymers Pq, Pio> P25> and P50 in solution at 298 K, and in a 2-methyltetrahydro-furan solvent glass at 77 K. These spectroscopic studies reveal that fluorescence from the 71,71" exciton state is observed at Amax=443 nm, 2.80 eV in the polymers P0-P50 at 298 and 77 K, but the intensity and lifetime of the fluorescence is quenched as the mole fraction of Re in the polymers is increased. This indicates that the metal chromophore quenches the 71,71" state. The quenching is inefficient even when the mole fraction is large, suggesting that interchain diffusion of the 71,71" exciton is slow compared to its lifetime [70]. Phosphorescence from the 71,71" state of the conjugated polymer backbone is observed at > max=b43 nm, 1.93 eV in P10-P50 at 77 K, and emission at Amax=690 nm, 1.8 eV is assigned to the d7i(Re) 7i oiy MLCT transition. 

The emission from [Ru(bpz)3] is quenched by carboxylic acids the observed rate constants for the process can be rationalized in terms of the protonation of the non-coordinated N atoms on the bpz ligands. The effects of concentration of carboxylate ion on the absorption and emission intensity of [Ru(bpz)3] have been examined. The absorption spectrum of [Ru(bpz)(bpy)2] " shows a strong dependence on [H+] because of protonation of the free N sites the protonated species exhibits no emission. Phosphorescence is partly quenched by HsO" " even in solutions where [H+] is so low that protonation is not evidenced from the absorption spectrum. The lifetime of the excited state of the nonemissive [Ru(Hbpz)(bpy)2] " is 1.1ns, much shorter than that of [Ru(bpz)(bpy)2] (88 nm). The effects of complex formation between [Ru(bpz)(bpy)2] and Ag on electronic spectroscopic properties have also been studied. Like bpz, coordinated 2,2 -bipyrimidine and 2-(2 -pyridyl)pyrimidine also have the... 

In summary, spectroscopic studies show that at low temperatures higher excited states of chromium(III) complexes undergo rapid internal conversion to the metastable T2g or 2Eg levels. Intersystem crossing from the 4T2g to the aEg level occurs with near unit efficiency in many chromium(III) complexes. Phosphorescence competes, usually unfavorably, with radiationless decay from the 2Eg state. Studies of the excited states of Mo(III), (4d)3, based on absorption spectra of its complexes in solution, have recently been reported.134-137... 

Spectroscopic evidence has also been adduced for the ability of the anthracene T2 to transfer energy to other substances.239 Selective excitation of guest anthracene in a host dibenzofuran crystal also containing napthalene-d8 as a guest resulted in naphthalene phosphorescence. As shown in Figure 8, the path of the energy is S0 -> Sj excitation of anthracene, intersystem crossing... 

Pauli principle, 45-47,178-182, 284-287 Pauli spin matrices, 96 P branch, 171-173,218,303 Peanuts, 320 Perpendicular band, 259, 265 Perturbation, spectroscopic, 283 Perturbation theory, 35-38,102 degenerate, 36-38 for nuclear motion, 149-159 time-dependent, 110-114 Phase, 13 Phenol, 225 Phosphorescence, 128 Phosphorous trichloride, structure of, 222, 223... 

Although the two compounds show similar photophysical behavior, the same is not true for their spectroscopic characteristics such as absorption, fluorescence, and phosphorescence maxima, where the bands in 43 are all red shifted relative to 44, suggesting less conjugation in the angular 44. In the case of 44, there is strong evidence for TTA in the singlet region. 

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