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At least 73 records · Page 4Linked to original sources

PubMed2000

High-efficiency fluorescent organic light-emitting devices using a phosphorescent sensitizer

To obtain the maximum luminous efficiency from an organic material, it is necessary to harness both the spin-symmetric and anti-symmetric molecular excitations (bound electron-hole pairs, or excitons) that result from electrical pumping. This is possible if the material is phosphorescent, and high efficiencies have been observed in phosphorescent organic light-emitting devices. However, phosphorescence in organic molecules is rare at room temperature. The alternative radiative process of fluorescence is more common, but it is approximately 75% less efficient, due to the requirement of spin-symmetry conservation. Here, we demonstrate that this deficiency can be overcome by using a phosphorescent sensitizer to excite a fluorescent dye. The mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as 100%. As an example, we use this approach to nearly quadruple the efficiency of a fluorescent red organic light-emitting device.

Journal Article↗

PubMed1979

Phosphorescence of protein-bound eosin and erythrosin. A possible probe for measurements of slow rotational mobility.

We used a pulsed dye laser working at 540 nm to excite triplet-state formation of eosin and erythrosin, either bound or unbound to bovine serum albumin, in aqueous solution anaerobically at pH 8 and 20-22 degrees C. Delayed emission from radiative transitions of the triplet state was readily detectable, both as delayed fluorescence and as red phosphorescence. Detection of the triplet state by measurement of phosphorescence at 645 nm upwards was at least 100-fold more sensitive than by absorbance measurements of ground-state depletion at 500 nm. When immobilized in poly(methyl methacrylate), the phosphorescence of eosin and erythrosin was polarized with an anisotropy parameter [Jablonski (1961) Z. Naturforsch. A16, 1-4] of about 0.25. The phosphorescence of erythrosin is sufficiently intense to be distinguishable from the long-wavelength end of fluorescence under conditions of continuous rather than pulsed excitation. Our observations suggest that phosphorescence depolarization of eosin or erythrosin probes could be used as a highly sensitive method of measuring rotational relaxation times in region from 10(-5) to 10(-3) s, such as those of the uniaxial rotation of membrane proteins.

Eosine Yellowish-(YS)↗

PubMed2004

Sensitized phosphorescence of benzil-doped ladder-type methyl-poly(para-phenylene).

The delayed luminescence and phosphorescence of ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with benzil at a concentration of 20% by weight has been measured. The introduction of benzil leads to a dramatic reduction of the polymer singlet emission. At the same time, a new band with maximum at 611 nm appears, corresponding to the phosphorescence of MeLPPP. The phosphorescence decay on the short time scale is close to an exponential law with a time decay of 15 ms. This indicates that benzil can efficiently sensitize the phosphorescence of the polymer. In addition, a broad and featureless emission is observed in the delayed luminescence spectra of benzil-doped MeLPPP, which is attributed to an exciplex formed between the polymer host and the dopant. We further observe that the delayed fluorescence is enhanced by the addition of benzil. It is concluded that the delayed fluorescence of benzil-doped MeLPPP is mainly due to the annihilation of triplet excitons on the polymer. Finally, efficient triplet-triplet energy transfer from the benzil-doped polymer to the red-emitting phosphorescent dye Pt(II)octaethylporphyrin is established.

Journal Article↗

PubMed1974

Room temperature phosphorescence and the dynamic aspects of protein structure.

While the phosphorescence of aromatic chromophores in solution is normally quenched through diffusion of dissolved oxygen and other solvent-mediated processes, the phosphorescence of some proteins in solution is observed at room temperature. The tryptophan phosphorescence arises from residues which are hindered from interaction with oxygen by the folding of the polypeptide chains. Measurements of the phosphorescence lifetime of horse liver alcohol dehydrogenase (alcohol: NAD(+) oxidoreductase, EC 1.1.1.1) as a function of oxygen concentration indicate that internal tryptophan residues are periodically exposed to oxygen. This permits the calculation of rate constants for conformational oscillations in the enzyme. The present article illustrates the feasibility of employing phosphorescence in the study of proteins in solution in general and the utility of such experiments in probing the dynamic aspects of protein structure.

Alcohol Oxidoreductases↗

PubMed1989

Analysis of aluminum and divalent cation binding to wheat root plasma membrane proteins using terbium phosphorescence.

A phosphorescent trivalent cation, terbium [Tb(III)], has been used to study the binding of different polyvalent cations to the proteins of wheat (Triticum aestivum L.) root plasma membranes. The phosphorescence emission intensity of Tb(III) was enhanced after Tb(III) binding to wheat root plasma membranes as a result of nonradiative resonance energy transfer from the membrane protein tyrosine and phenylalanine residues. Complex, saturable Tb(III) binding was observed, suggesting multiple binding sites. Bound Tb(III) could be displaced by divalent cations in the general order: Mn(II) > Ca(II) > Mg(II). Al(III) was very effective in reducing the protein-enhanced Tb(III) phosphorescence at pH values below 5. Al(III) also altered the Tb(III) phosphorescence lifetime, suggesting Al(III)-induced changes in membrane protein conformation. The more Al(III)-sensitive wheat cultivar (Anza) bound Al(III) with higher affinity than the more tolerant cultivar (BH 1146). At pH 5.5 where Al(III) did not displace bound Tb(III), low levels of Al(III) reduced the ability of Mn(II) to decrease Tb(III) phosphorescence. The significance of these results is discussed with respect to the mechanisms of Al(III) tolerance in wheat and the potential beneficial effects of Al(III) in reducing Mn(II) phytotoxicity.

Journal Article↗

PubMed1993

Tryptophan phosphorescence as a structural probe of mitochondrial F1-ATPase epsilon-subunit.

We report the detection of tryptophan phosphorescence emission from the sole residue in the epsilon-subunit of the bovine heart mitochondrial F1-ATPase complex. The phosphorescence spectrum, intensity and decay kinetics have been measured over the temperature range 160-273 K. The fine structure in the phosphorescence spectrum at low temperature, with the 0-0 vibrational band centered at 411 nm, reveals the hydrophobic nature of the chromophore's environment. Both the large width of the 0-0 vibrational band and the heterogeneous decay kinetics in fluid solution emphasize the existence of multiple conformations of the epsilon-subunit, structures which are rather stable as they do not interconvert in the millisecond time scale. Further, from the relatively long triplet lifetime at 273 K, it is possible to infer the existence of a tight, rigid core in the structure of the epsilon-subunit. Under subunit-dissociating conditions (6 M urea), the spectrum at 160 K undergoes a slight blue shift but since the phosphorescence lifetime, at all temperatures, is similar or longer than in the absence of dissociant, we conclude that dissociation does not lead to solvent exposure of the tryptophanyl side-chain. This conclusion is supported by the results obtained at 273 K by dissociating F1 in the presence of 0.3 M guanidine hydrochloride. Phosphorescence lifetimes indicate that 6 M urea leads to a more compact structure of the epsilon-subunit, whereas the opposite occurs when Mg-ATP is added to nucleotide-depleted F1. These spectroscopic changes establish unequivocally that the binding of the adenine nucleotide to the enzyme is accompanied by conformational changes involving the epsilon-subunit.

Adenosine Triphosphate↗

PubMed1997

Room temperature phosphorescence study of phosphate binding in Escherichia coli alkaline phosphatase.

The phosphorescence spectrum and decay of Trp109 in Escherichia coli alkaline phosphatase was measured for the enzyme in 10 mM Tris/HCl, pH 7.4, at 21 degrees C. Changes in the spectrum and decay from the steady-state in response to non-covalent phosphate binding suggested a phosphate-induced alteration in the local environment surrounding Trp109 which lies buried below the active site. The seemingly inflexible structure in the region of Trp109, as judged by its very long phosphorescence lifetime, appeared unaltered when the enzyme was symmetrically bound with phosphate. However, the protein with phosphate bound to only one site displayed a marked increase in flexibility that extended over both subunits. For ratios of phosphate/enzyme (mol/mol) between 1.0 and 2.0, the observation of exponential phosphorescence decays with lifetimes that are a function of dilution provided evidence for the rapid exchange between phosphate half-saturated and fully-saturated enzymes consistent with observed enzyme turnover rates. The lifetimes under these conditions result in the calculation of a Kd for the dissociation of phosphate from the doubly occupied enzyme of 1.1 +/- 0.1 microM. The non-exponential decays at P/Ed (phosphate/dimeric enzyme) ratios less than 1.0 revealed that the exchange of phosphate between phosphate-free and half-saturated enzymes was not occurring on the timescale of the phosphorescence decay times, which implied that the half-saturated molecule cannot be contributing significantly to catalysis under steady-state conditions. The observation that the phosphorescence decay at a P/Ed ratio of 1.0 is exponential with a lifetime characteristic of the half-saturated species indicates that the binding of the first phosphate is significantly greater than the second, or that the binding exhibits negative cooperativity.

Alkaline Phosphatase↗

PubMed1993

Phosphorescence lifetime studies of interactions between serum albumins and sodium dodecyl sulfate.

Binding of sodium dodecyl sulfate (SDS) to bovine serum albumin (BSA) and human serum albumin (HSA) in aqueous solutions at room temperature induces significant changes in the phosphorescence lifetime of tryptophan (Trp) residues. A steep rise of the phosphorescence lifetime from 1.9 ms to 10.0 ms for BSA and from 1.9 ms to 5.5 ms for HSA is observed when the total SDS concentration increases from 0.0 mM to 0.22 mM at 1 mg/mL protein concentration. As the total SDS concentration is further increased to 2.2 mM, a slower increase in the phosphorescence lifetime is observed, from 10.0 ms to 19.5 ms for BSA and from 5.5 ms to 7.2 ms for HSA. It appears that the phosphorescence lifetime modifications are mainly due to an increase of protein matrix rigidity around Trp residues. The observed differences (between HSA and BSA) allow us to distinguish the contribution of the two Trp residues to the BSA phosphorescence.

Humans↗

PubMed2005

Erythrosin B phosphorescence monitors molecular mobility and dynamic site heterogeneity in amorphous sucrose.

Molecular mobility modulates the chemical and physical stability of amorphous biomaterials. This study used steady-state and time-resolved phosphorescence of erythrosin B to monitor mobility in thin films of amorphous solid sucrose as a function of temperature. The phosphorescence intensity (lifetime), emission energy, and red-edge excitation effect were all sensitive to localized molecular mobility on the microsecond timescale in the glass and to more global modes of mobility activated at the glass transition. Blue shifts in the emission spectrum with time after excitation and systematic variations in the phosphorescence lifetime with wavelength indicated that emission originates from multiple sites ranging from short lifetime species with red-shifted emission spectrum to long lifetime species with blue-shifted emission spectrum; the activation energy for nonradiative decay of the triplet state was considerably larger for the blue-emitting species in both the glass and the melt. This study illustrates that phosphorescence from erythrosin B is sensitive both to local dipolar relaxations in the glass as well as more global relaxations in the sucrose melt and provides evidence of the value of phosphorescence as a probe of dynamic site heterogeneity as well as overall molecular mobility in amorphous biomaterials.

Biocompatible Materials↗

PubMed1998

Singlet molecular oxygen in photobiochemical systems: IR phosphorescence studies.

Singlet molecular oxygen (1O2) is one of the most active intermediates involved in photosensitized oxygenation reactions in chemical and biological systems. Deactivation of singlet oxygen is accompanied by infrared phosphorescence (1270 nm) which is widely employed for 1O2 detection and study. This review considers techniques for phosphorescence detection, phosphorescence spectra, quantum yields and kinetics under laser excitation, the radiative and real 1O2 lifetimes in organic solvents and water, 1O2 quenching by biomolecules, and estimation of singlet oxygen lifetimes, diffusion lengths and phosphorescence quantum yields in blood plasma, cell cytoplasm, erythrocyte ghosts, retinal rod outer segments and chloroplast thylakoids. The experiments devoted to 1O2 phosphorescence detection in photosensitizer-containing living cells are discussed in detail. Information reviewed is important for understanding the mechanisms of photodestruction in biological systems and various applied problems of photobiology and photomedicine.

Humans↗

PubMedDate not supplied

[Phosphorescent analysis of lipid peroxidation products in liposomes].

It was found that lipid peroxidation products incorporated into liposomes prepared from oxidized preparations of bovine heart phosphatidylcholine and the total lipid fraction of human erythrocyte membranes are able to phosphoresce at room temperature was studied. The temperature dependences of kinetic and spectral parameters of phosphorescence were measured. It is shown that mechanism of phosphorescence quenching of lipid chromophores has a dynamic nature. It is proposed to use endogenic molecules of the lipid peroxidation products capable of phosphorescence as intrinsic phosphorescence probes for studying the slow molecular dynamics of lipids in artificial and biological membranes in a millisecond range.

Animals↗

PubMedDate not supplied

[Phosphorescence of octaethylchlorine, isobacteriooctaethylchlorine and their metal complexes].

The phosphorescence of dihydrooctaethylporphin (octaethylchlorin or OEC), of its complexes with magnesium, zinc, copper and palladium, and of zinc and palladium complexes of isobacteriooctaethylchlorin (5,6,7,8-tetrahydrooctaethylporphin with adjacent hydrogenated pyrrole rings or THOEP-ADJ) has been investigated. The phosphorescence spectra and phosphorescence excitation spectra as well as the ratio of fluorescence and phosphorescence yields and the triplet state lifetume have been measured. It has been shown that the singlet-triplet interval is about 4100 cm-1 for OEC complexes and about 4300 cm-1 for THOEP-ADJ complexes, and depends wealky on the nature of the metal atom forming the complex. The triplet level position of chlorophyll alpha is discussed. It is concluded that the maximum of chlorophyll alpha phosphorescence spectrum must be located at 895 nm.

Copper↗

PubMedDate not supplied

[Phosphorescence analysis of the chlorophyll triplet state in preparations of photosystem II].

The low-temperature (77 K) phosphorescence of chlorophyll (Chl) in the reaction centres (D1D2-cyt b559-particles) and the core complexes of photosystem II isolated from higher plants was studied. Two phosphorescence spectral bands with the emission maxima at 950 and 977 nm, excitation maxima at 666 and 675-680 nm, and the lifetimes equal to 2 and 1.5 ms, respectively, were registered. The data indicate that the phosphorescence corresponds to the triplet Chl a molecules spatially separated from carotenoids. In samples treated by potassium ferricyanide and frozen under illumination by red light, the intensities of both bands were reduced, but the decrease of the short-wavelength 950-nm band was much more pronounced. This allows an assumption that the short-wavelength phosphorescence belongs to Chl a molecules, which are more accessible for ferricyanide because they are located on the surface of the chlorophyll-protein complexes, whereas the long-wavelength phosphorescence is emitted by the Chl molecules located inside the D1D2 heterodimer and therefore, is more protected by protein macromolecules.

Chlorophyll↗

PubMedDate not supplied

[Chlorophyll phosphorescence in chloroplasts and their fragments].

Spectral parameters, decay time and quantum yield of low temperature (--196 degrees) delayed luminescence of chloroplasts and chloroplasts fragments have been investigated. It has been shown that the fragments enriched in photosystem 2, photosystem 1 of stroma or grana, obtained by differential centrifugation after digitonin treatment produce a delayed emission with components similar to that of initial chloroplasts, normal leaves and alga; i. e. phosphorescence (maximum 960--980 nm) and delayed fluorescence (maxima at 690 and 740 nm) of chlorophyll and phosphorescence of pigments of different nature (780--820 nm). Excitation spectra of chlorophyll phosphorescence have the maximum at 669 +/- 1 nm and shoulder at 650 nm. The quantum yield of chlorophyll phosphorescence in chloroplast is found to be lower than that of chlorophyll in ethanol by the factor of 200. It increases with destruction of initial structures reaching the maximal value in the most light fragments. The data suggest that the luminescence studied accompanies desactivation of the triplet states of the chlorophyll molecules involved in the photosynthetic pigment complex. On the basis of previous studies it has been proposed that the increase of phosphorescence intensity in the light particles is due to disturbances in the pigment complex leading to a decrease of triplet-triplet energy transfer from chlorophyll to carotenoids.

Carotenoids↗

PubMed1998

Comparison of the time-resolved absorption and phosphorescence from the tryptophan triplet state in proteins in solution.

Measurement of the room temperature Trp triplet state lifetime in proteins by time-resolved phosphorescence can provide valuable information on the structure and dynamics of proteins in solution. Our time-resolved absorption measurements on the long-lived states resulting from electronic excitation of the chromophore demonstrate the presence of more complex behavior than revealed by time-resolved phosphorescence. To provide additional insight into this behavior, a comparative study of time-resolved transient absorption and time-resolved phosphorescence of proteins in solution was carried out. The results show that the time evolution of the long-lived states observed through transient absorption often differs considerably from that observed in time-resolved phosphorescence. In some proteins, the presence of competing reactions complicates the interpretation of the transient absorption measurements (which may affect the phosphorescence yield). A more complete characterization of these processes will likely prove useful in the study of protein structure and dynamics in solution.

Alkaline Phosphatase↗

PubMed1998

In vivo tissue pO2 measurements in hamster skinfold by recessed pO2 microelectrodes and phosphorescence quenching are in agreement.

OBJECTIVE: Phosphorescence quenching has been used successfully to optically measure in vivo blood pO2 in the microvasculature. Optical measurements have also been made in some tissues, but it is not clear whether these results accurately reflect tissue pO2. METHODS: Recessed pO2 microelectrodes and the phosphorescence quenching technique were used simultaneously to measure in vivo tissue pO2 in hamster skinfold. The optical window for phosphorescence quenching was focused around the tips of microelectrodes that were positioned in tissue regions at least 100 microns from large microvessels. RESULTS: Mean tissue pO2 measured by recessed pO2 microelectrodes was 18.4 +/- 1.7 (SE) Torr, and mean tissue pO2 determined from the time course of phosphorescence decay was 18.8 +/- 2.0 Torr (no significant difference). The two tissue pO2 measurements agreed over a wide range, from 2 to 46 Torr (r = 0.93, 39 paired measurements from six sites in 3 animals). There was no systematic change in the microelectrode tissue pO2 during the period of light excitation used for the optical method. CONCLUSIONS: Under the conditions of our study, sufficient amounts of porphyrin dye leaked from the vasculature and diffused into tissue, allowing accurate measurements of tissue pO2 by the phosphorescence quenching technique. Furthermore, the optical method did not deplete significant amounts of O2 from tissue during light excitation.

Animals↗

PubMed2000

Quenched phosphorescence, a new detection method in capillary electrophoresis.

The applicability of quenched phosphorescence as a detection mode in capillary electrophoresis (CE) was explored for a number of analyte classes and buffer systems. The detection method is based on the quenching of biacetyl phosphorescence (biacetyl is a constituent of the CE buffer) by the analytes via various mechanisms (energy transfer, electron transfer and, possibly, hydrogen donation) and gives rise to negative peaks in the electropherograms. A number of buffers in the pH range 4.7-11.5, frequently used in CE, were tested for their compatibility with this detection mode. Borate, succinate, malonate, acetate, and phosphate buffers (pH 4.7-8.5) could be used without any problems. With a pH of ca. 8.5 or higher the baseline declined with time, while at a pH higher than 9.5 no signal at all was obtained. Obviously, the noise on the phosphorescence signal (i.e., the baseline) determines the ultimate analyte detection limits (LODs). The baseline signal-to-noise ratio, usually denoted as the dynamic reserve (DR), was enhanced ca. 25-fold compared to direct biacetyl excitation by sensitization of the biacetyl phosphorescence by 1,5-naphthalenedisulfonic acid, and by application of a total emission mirror (TEM). A concentration of 1 x 10(-3) M 1,5-naphthalenedisulfonic acid was found to be optimal. For the buffer systems considered, the DR was typically ca. 300-600 under optimized conditions (noise defined as 1 x sigma). Investigated analytes include naphthalenesulfonic acids (NS), nitrophenols, hydroxybenzoic acids, amino acids, and dithiocarbamates (DTCs.). For most of these, the LODs were in the 10(-7)-10(-8) M range, which is significantly lower than with direct or indirect absorption detection.

Amino Acids↗

PubMedDate not supplied

Comparison of properties on non-protected fluid room temperature phosphorescence of some tetra-ring aromatic hydrocarbons.

A comparative study of the photoluminescence properties of three kinds of tetra-ring aromatic hydrocarbon (1-sodium pyrenesulphonate, benz[alpha]anthracene and chrysene) solution in the absence of any protecting medium is described. It was found that a room temperature phosphorescence signal with different intensities can be induced for these solutions, using only TlNO3 or KI as a heavy atom perturber (HAP) and Na2SO3 as a deoxygenator. An appropriate amount of organic solvent added to the systems of pyrene, benz[alpha]anthracene and chrysene is necessary for increasing the solubility and phosphorescence intensity, and the preferable solvent is acetonitrile. For the pyrene, pyrenesulphonate and chrysene systems, a delayed excimer fluorescence accompanied with the room temperature phosphorescence (RTP) emission can be observed, but that for benz[alpha]anthracene cannot. The ratio of delayed excimer fluorescence and phosphorescence signals for pyrene, pyrenesulphonate and chrysene systems can be controlled by adjusting the concentration of luminophor, kinds and amount of both organic solvents and HAP. Under the optimal conditions, the RTP signals are proportional to the concentration of the four aromatic hydrocarbons, which means that the RTP properties of the four tetra-ring aromatic hydrocarbons can be used for quantitative analysis.

Cyclization↗