Phosphorescence lifetime and spectra

Phosphorescence is readily detectable from most types of proteins at room temperature. Tryptophan phosphorescence lifetimes and yields are very sensitive to environment, and therefore phosphorescence is sensitive to conformational changes in proteins. Fundamental questions concerning exactly what parameters affect lifetime and spectra of tryptophan in proteins remain still to be answered. 

Several bacterial antibiotics which contain phenylalanine as their only aromatic chromophore have been shown to exhibit luminescence spectra virtually identical to that of free phenylalanine 28b) although in one case to8) more highly resolved fine structure was attributed to the phenylalanine being in a hydrophobic environment. Phosphorescence lifetimes and fluorescence to phosphorescence ratios show only minor variations for a variety of phenylalanine-containing peptides... 

Burrell and Hurtubise (.32) investigated calibration curves extended well beyond the normal linear range for RTF and RTF of benzoCf)quino-line adsorbed on a silica gel chromatoplate under neutral and acidic conditions. As the benzoCf)quinoline concentration increased, the RTF curves leveled off, whereas the RTF curves passed through a maximum and then decreased. The extended calibration curves along with fluorescence and phosphorescence spectra and phosphorescence lifetimes for benzoCf)quinoline revealed differences in the RTF and RTF phenomena. For example, it was determined that RTF could arise from molecules adsorbed on the surface and in multilayers of molecules, whereas phosphorescence was only generated from molecules adsorbed on the surface of the chromatoplate and not in the multilayers. ... 

The absorption bands measured by the flash spectrographic method are often assigned by (a) comparison with known singlet-singlet absorption spectra, (b) comparison of the lifetime of the species responsible for the absorption with the phosphorescence lifetime, (c) comparison with calculated energies and intensities of the various possible absorptions by semi-empirical molecular orbital methods, and (d) comparison with published triplet absorption spectra and decay kinetics of model compounds. 

Figure 1. Uncorrected phosphorescence excitation and emission spectra of dimethyl terephthalate (5 X 10 3M) in 95% ethanol at 77 K, excitation scan Em A 418 nm emission scan Ex A 250 nm lifetime (t) 2.2 sec (9)...

The uncorrected phosphorescence excitation and emission spectra of PET yarn at 77°K show an excitation maximum at 310 nm and emission at 452 nm with a lifetime, t, equal to 1.2 seconds... 

In 1962, Parker and Hatchard described a photoelectric spectrometer for phosphorescence measurements with which they were capable of obtaining phosphorescence spectra, and of determining lifetimes and quantum efficiencies of a large number of organic compounds. This work stimulated intensely the interest in the phosphorimetry of diverse chemical analytes [5], and one year later, Wine-... 

Room temperature phosphorescence can be observed from dried proteins. Sheep wool keratin(47) has a phosphorescence lifetime of 1.4 s. Six lyophilized proteins were shown to exhibit phosphorescence at room temperature.(48) The spectra were diffuse, and the lifetime was non-single-exponential, which the authors interpreted as due to inhomogeneous distribution of tryptophans. As the protein was hydrated, the phosphorescence lifetime decreased. This decrease occurred over the same range of hydration where the tryptophan fluorescence becomes depolarized. Hence, these results are consistent with the idea that rigidity of the site contributes to the lifetimes. 

For single-tryptophan proteins there is some correlation between blue-shifted fluorescence emission maximum and phosphorescence lifetime (Table 3.2). Another correlation is that three of the proteins which exhibit phosphorescence, azurin, protease (subtilisin Carlsberg), and ribonuclease Tlt are reported to show resolved fluorescence emission at 77 K. Both blue-shifted emission spectra and resolved spectra are characteristic of indole in a hydrocarbon-like matrix. 

Emission electronic spectra of dioxins are characterized by phosphorescence and very low intensity fluorescence. The phosphorescence lifetime was found to change slowly as the number of the chlorine atoms varies in a dioxin molecule <2000JST(553)243>. 

Norrish Type I reactions occur from 7 only if the state is 3(rc,7r ). Compound 53 has a phosphorescence lifetime of 10 3 sec, and there is a mirror-image relationship between its closely spaced phosphorescence and absorption spectra. Compound 54, however, has a phosphorescence lifetime of 5.5 sec, and there is a large Stokes shift between its dissimilar absorption and phosphorescence spectra. Apparently both compounds have a lowest (n, r ) singlet,... 

The polarized phosphorescence spectra of 1,5-naphthyridine and its d6 isomer in durene and in durene-d14 mixed crystals have been obtained at 4°K. The lowest singlet state is at 27123 and 27200 cm-1, whereas the corresponding triplet state is at 23215 and 23288 cm 1 for the proto and deutero compounds, respectively. The phosphorescence lifetime in durene crystals is 0.23 sec.140 The polarized spectra (4°K) of 1,5-naphthyridine and its d6 isomer in naphthalene have also been examined. There is a difference between the spectra in naphthalene and in durene attributable to a decrease in the strong vibronic coupling that is considered to exist between the n- n state and the higher n -> n states.141 TheEPR spectrum of 1,6-naphthyridine in its lowest triplet state has been observed for solid solutions in single crystals of durene. The nuclear hyperfine structure allows an estimate of 0.14 to be made for the spin density on the nitrogen atom in the 1-position.142... 

Modifications to the experimental set-up for the acquisition of fluorescence spectra from samples within the ESR microwave cavity are described in previous work ( ). Further improvements using a fast photomultiplier/photon counting technique were made in an attempt to determine the radiative fluorescence lifetime in solution. Phosphorescence at 77 K was measured both by a conventional Varian spectrofluorimeter and a pulsed laser/cooled diode array imaging device. Radiative phosphorescence lifetimes were measured by the photon counting technique, using the Stanford Research System SR400 gated photon counter. 

Europium(III) exchanged zeolites have been studied by a number of research groups. Arakawa and coworkers (20, 21 ) report the luminescence properties of europium(III)-exchanged zeolite Y. Emission spectra were measured under a variety of conditions and bands for europium(II) were observed after thermal treatment of the europium(III) Y zeolites. A mechanism was proposed for the thermal splitting of water which involved the cycling of europium between the two different oxidation states. Europium MSssbauer experiments (22 ) also show that on thermal treatment of europium-(III) zeolites that europium(II) is formed. Stucky and coworkers (23, 24) studied the phosphorescence lifetime of these europium-(lll) zeolites and showed that the inverse of the lifetime (the decay constant) was linearly related to the number of water molecules surrounding the europium(III) ion in the zeolite supercages. These studies involved zeolites A, X, Y and ZSM-5. 

The wavelength of the spectra scarcely changed when observed at 77 and 298 K. whereas the yield (or intensity) of the phosphorescence at 77 K (Fig. 19, spectrum a) was remarkably high compared with the yield at 298 K. This result can be attributed to the fact that the lifetime of the charge-transfer excited triplet state is markedly affected by temperature-dependent radiationless processes. Such radiationless deactivation from the excited triplet state becomes less efficient as the temperature decreases, leading to an elongation of the phosphorescence lifetime from T298 140... 

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