Decrease In Phosphorescence Intensity Research Articles

Phosphorescent ruthenium complexes with bromopyrene unit that enhance oxygen sensitivity

Ruthenium complexes are very useful phosphorescent probes for the visualization of hypoxia. We designed and synthesized three ruthenium complexes possessing bromopyrene, naphthalene, or anthracene units to improve the oxygen response. These ruthenium complexes provided strong phosphorescence under hypoxic conditions, while an increase in oxygen concentration led to a decrease in phosphorescence intensity. Among the ruthenium complexes, that with a bromopyrene unit (Ru-BrPy) had the best properties. This showed good cellular uptake and bright emission in cells, and had the highest sensitivity for molecular oxygen. Thus, Ru-BrPy is a promising candidate as a molecular probe for detecting cellular hypoxia.

Optimization of coupled plasmonic effects for viable phosphorescence of metal-free purely organic phosphor

Metal-free purely organic phosphorescent molecules are attractive alternatives to organometallic and inorganic counterparts because of their low cost and readily tunable optical properties through a wide chemical design window. However, their weak phosphorescent intensity due to inefficient spin-orbit coupling and, consequently, prevailing non-radiative decay processes limit their practical applicability. Here, we systematically studied phosphorescence emission enhancement of a purely organic phosphor system via plasmon resonance energy transfer. By precisely tuning the distance between purely organic phosphor crystals and plasmonic nanostructures using layer-by-layer assembled polyelectrolyte multilayers as a dielectric spacer, maximum 2.8 and 2.5 times enhancement in photoluminescence intensity was observed when the phosphor crystals were coupled with ∼55 nm AuNPs and ∼7 nm AgNPs, respectively, at the distance of 9.6 nm. When the distance is within the range of 3 nm, a dramatic decrease in phosphorescence intensity was observed, while at a larger distance, the plasmonic effect diminished rapidly. The distance-dependent plasmon-induced phosphorescence enhancement mechanism was further investigated by time-resolved photoluminescence measurements. Our results reveal the correlation between the amplification efficiency and plasmonic band, spatial factor, and spectral characteristics of the purely organic phosphor, which may provide an insightful picture to extend the utility of organic phosphors by using surface plasmon-induced emission enhancement scheme.

Influence of high-temperature oxidation on photoluminescent properties of white Si[sbnd]O[sbnd]C(–H) ceramics

SiOC(–H) ceramics were prepared by pyrolyzing densely cross-linked polysiloxane particles in hydrogen at temperatures of 800, 900 and 1100°C. Thermogravimetric–differential thermal analysis (TG–DTA) curves of these SiOC(–H) ceramics in an air flow revealed that the oxidation resistance strongly depended on the decarbonization temperature. On the other hand, these decarbonized samples were oxidized in dry air flow at temperatures of 300, 500, 700, 1000 and 1200°C. After the oxidation in air, photoluminescent (PL) spectra and Fourier transform infrared (FTIR) spectra of the oxidized samples were investigated. In partly organic SiOC(–H) ceramics with high H/C ratios, the intensity of blue PL simultaneously decreased with rapid oxidation. Residual weak PL peaks are probably assigned to defects in silica formed on particle surfaces. In dense SiOC(–H) ceramics with a relatively low H/C ratio, the intensity of white PL gradually decreased with moderate oxidation and the PL peak position shifted to longer wavelengths. Intensity of phosphorescence of the dense SiOC(–H) ceramics was also weakened after oxidation. The decrease of phosphorescence intensity, however, began at a rather low temperature range as compared with that of the apparent PL.

Decay dynamics of phosphorescence in CaGa 2S 4:Eu 2+

CaGa 2S 4:Eu 2+ doped with rare-earth ions is a prospective material for optoelectronics and photonic applications due to an attractive combination of their favorable physical properties. The study of decay dynamics of phosphorescence in CaGa 2S 4:Eu 2+ was undertaken in order to advance the fundamental understanding of the processes involved in luminescence phenomenon. At very low temperatures the phosphorescence of CaGa 2S 4:Eu 2+ decays exponentially with a decay time of 420 s. However, at higher temperatures the phosphorescence intensity decreases with time following power law, in which decay constant changes with temperature. On the basis of the rate equation, expressions are derived for the decay of phosphorescence intensity and they are as given below: I=I 0 exp( −t/ τ) , and I=I 0 t −α , where τ is the decay time and α is the decay constant. The first equation expressing exponential decay is suitable to explain the phosphorescence dynamics at low temperature and the second equation related to the power law decay is suitable to explain the phosphorescence dynamics at higher temperature. At very low temperature of 9 K, the decrease in phosphorescence intensity follows a single exponential decay, indicating the monomolecular kinetic, which is consistent with trapping levels close to Eu 2+ sites. A good agreement found between the experimental and theoretical results supports the fact that the thermally released charge carriers from traps recombine radiatively at Eu 2+ sites. The value of decay constant α in 100–300 K temperature range varies in a non-monotonic way between 0.8 and 1.8 and this fact indicates the presence of defect distributions.

Determination of Trace Bismuth by a Solid Substrate Room Temperature Phosphorescence Quenching Method Based on Anionic Polymeric Acryclic Acid Lead Particles Containing Luminescent Eosine Molecules

Luminescent particles of Anionic Polymeric Acryclic Acid Lead (Pb(PAA)2) which containing eosine(HFInBr4), Eosine nanomicroball of anionic polypropylene acid lead contained luminophores (short for E.N.PAA.L.C.L), were synthesized by a sol‐gel method, using anionic polymeric acryclic acid sodium (PAANa) as the precursor and Pb2+ as the precipitant. NH4Ac‐HAc can react with the Pb2+ in E.N.PAA.L.C.L, causing it to decompose into aqueous soluble components. E.N.PAA.L.C.L‐ NH4Ac‐HAc can emit strong and stable solid substrate room temperature phosphorescence (SS‐RTP) on filter paper, and bismuth, mercury or iodine can cause a decrease in phosphorescence intensity. Based on the facts above, a new method for the determination of trace bismuth by an SS‐RTP quenching method was established. The linear range of this method was 0.01–0.20(pg spot−1) (4.0×10−12 g ml−1) of Bi3+, with a detection limit (LD) of 0.0016 pg spot−1, and the regression equation of the working curve was ΔIp=61.01+237.8 mBi3+ (pg spot−1), r=0.9992. This method was applied to the determination of trace bismuth in human hair and well water samples with satisfactory results. The mechanism of SS‐RTP emission was also discussed.

Determination of Trace Copper by Solid Substrate–Room Temperature Phosphorescence Quenching Method Based on Lead Carboxymethyl Cellulose [Pb(CMC)2] Particles Containing Luminescent Salicyl Fluorones Molecules

Luminescent particles of lead carboxymethyl cellulose [Pb(CMC)2] that contain luminescent salicyl fluorones (SAF) {[Pb(CMC)2]‐SAF} were synthesized by sol‐gel method, using sodium carboxymethyl cellulose (NaCMC) as precursor and Pb2+ as precipitator. [Pb(CMC)2]‐SAF can emit intense and stable solid substrate–room temperature phosphorescence (SS‐RTP) on filter paper. EDTA (ethylenediaminetetraacetic acid) can chelate the Pb2+ in [Pb(CMC)2]‐SAF, causing it to decompose into aqueous soluble components PbY2–, CMC–, and SAF, and these components can react with Cu2+ to form [Cu(CMC)2]‐SAF, causing decrease of phosphorescence intensity. Based on the facts above, a new method for the determination of trace mercury by SS‐RTP quenching method was established. This method has been applied to the determination of trace copper in human hair and tea samples with satisfactory results.

Characteristic features of carbazole phosphorescence quenching by benzophenone molecules in toluene at 77 K

We have studied the characteristic features of carbazole phosphorescence quenching by benzophenone in toluene at 77 K. We have shown that the decrease in the relative phosphorescence intensity for carbazole (energy donor) by a greater factor than we see for the relative change in its decay time is due to the fact that a change in the phosphorescence decay time occurs only for carbazole molecules participating in triplet-triplet energy transfer, while the substantial decrease in the phosphorescence intensity for carbazole with no change in the phosphorescence decay time is connected with quenching of its singlet states.

Determination of trace silver by solid substrate room temperature phosphorescence quenching method based on lead carboxymethyl cellulose particles (Pb(CMC) 2) containing luminescent salicyl fluorenes molecules

Luminescent particles of lead carboxymethyl cellulose (Pb(CMC) 2) containing salicyl fluorones (THBF), Pb(CMC) 2-THBF were synthesized by the sol–gel method, using sodium carboxymethyl cellulose (NaCMC) as precursor and Pb 2+ as precipitant. Pb(CMC) 2-THBF can emit the intense and stable solid substrate room temperature phosphorescence (SS-RTP) on filter paper. And EDTA can chelate Pb 2+ in Pb(CMC) 2-THBF, causing it to decompose into aqueous soluble components PbY 2−, CMC − and THBF, which can react with Ag + to form Ag(CMC) 2-THBF, causing the decrease of phosphorescence intensity. Based on the facts above, a new method for the determination of trace silver by SS-RTP quenching method was established. The linear range of this method is 8.0–40.0 fg spot −1 (20.0–100.0 pg ml −1), with a detection limit (LD) of 2.2 fg spot −1 (corresponding to a concentration range of 5.5 × 10 −13 g ml −1), and the regression equation of working curve is Δ I p = 12.56 + 0.5527C Ag+ (fg spot −1, 0.4 μl spot −1), n = 8, r = 0.9992. This method has been applied to the determination of trace silver in human hair and tea sample with satisfactory results. The mechanism of SS-RTP emission is also discussed.

Determination of trace mercury by solid substrate room temperature phosphorescence quenching method based on lead carboxymethyl cellulose (Pb(CMC) 2) particles containing luminescent salicyl fluorones molecules

Luminescent particles of lead carboxymethyl cellulose (Pb(CMC) 2), which contains salicyl fluorones (THBF), Pb(CMC) 2-THBF, were synthesized by sol–gel method. Pb(CMC) 2-THBF can emit intense and stable solid substrate room temperature phosphorescence (SS-RTP) on filter paper. EDTA can chelate the Pb 2+ in Pb(CMC) 2-THBF, causing it decompose into aqueous soluble components PbY 2−, CMC − and THBF, and these components can react with Hg 2+ to form (CMC) 2Hg-THBF, causing decrease of phosphorescence intensity. Based on the facts above, a new method for the determination of trace mercury by SS-RTP quenching method was established. The linear range of this method is 2.0–40.0 fg spot −1 (5.0–100.0 pg ml −1) of Hg 2+, with a detection limit (LD) of 0.26 fg spot −1, and the regression equation of working curve is Δ I p = 13.02 + 1.165 m H g 2 + (fg spot −1, 0.4 μl spot −1), r = 0.9994. This method has been applied to the determination of trace mercury in water sample with satisfactory results. The mechanism of SS-RTP emission is also discussed.

Decrease in fluorescence and phosphorescence intensity of nylon 66 impurities by exposure to ultraviolet radiation

AbstractThe effects of exposure to ultraviolet radiation on the fluorescence and phosphorescence intensity of impurities in nylon 66, sometimes called gel, were measured using color image processing. The fluorescence intensity of the gel particles and of the polymer showed an approximately exponential decay with the time of exposure to ultraviolet radiation, with decay constants in the range 0.5 to 1.0 h−1. Analysis of images that were acquired over several hours also indicated a decrease in the phosphorescence intensity of the gel particles. Image processing provides a simpler and less expensive method of luminescence analysis than the spectroscopic techniques used previously to examine the effects of exposure to ultraviolet radiation on the phosphorescence properties of nylon 66 impurities. © 1995 John Wiley & Sons, Inc.

TEMPERATURE DEPENDENCE OF TRYPTOPHAN PHOSPHORESCENCE IN PROTEINS

The phosphorescence yield and decay kinetics of tryptophan (Trp) in apoazurin from Pseudomonas aeruginosa, subtilisin Carlsberg, Staphylococcal nuclease and liver alcohol dehydrogenase were determined as a function of temperature from 150 K (glassy matrix) to 300 K (fluid solution). The constancy of the lifetime-normalized phosphorescence yield with apoazurin and with Trp-314 in alcohol dehydrogenase establishes that the intersystem crossing quantum yield is practically unaffected across the temperature range. Consequently, any decrease in phosphorescence intensity not accounted for by lifetime-shortening is a signal either of the selective quenching of specific Trp residues in the same macromolecule or that the protein sample is heterogeneous in its emission properties. From an analysis of the thermal profile it is concluded that subtilisin Carlsberg and S. nuclease, as opposed to apoazurin, are not phosphorescent at ambient temperature, their residual emission probably arising from protein impurities. Criteria for distinguishing conformer emission from a contribution by protein impurities are discussed.

The lowest triplet state of Zn porphin

Phosphorescence microwave double resonance experiments are reported on Zn porphin at 1·2 K. In glassy solution very broad resonance transitions are observed. However, for Zn porphin in a crystalline n-octane matrix—a system known for its sharp optical spectra (Shpolskii effect)—three pairs of microwave transitions with widths of a few MHz are found, all of them corresponding to a decrease in phosphorescence intensity. By studying the behaviour of the signals for various methods of preparation of the sample and as a function of the optical bandwidth of excitation and detection, one pair of transitions could be assigned to monomeric solute molecules. The corresponding zero-field splittings are |X - Z| = 1355, |Y - Z| = 806 MHz. It was further established that by ‘pumping’ either of these transitions a third one can be detected at the difference frequency, so that the order of the levels must be X> Y>Z (or reverse). The results indicate that the molecule no longer possesses a four-fold axis in the excited st...

Pressure Dependence of Benzophenone Phosphorescence

The phosphorescence spectrum, intensity, and lifetime of benzophenone have been studied at 77°K as a function of pressure (0–30 kbar) in EPA, polymethylmethacrylate (PMMA), and polyethylene (PE). At 30 kbar the tiplet energy is raised 90 cm−1 in EPA and lowered about 460 cm−1 in PMMA and PE, according to the pressure-induced, reversible shift of the band origin. The triplet lifetime in EPA is reduced from 5.8 to 4.5 msec at 30 kbar pressure. A decrease in phosphorescence intensity suggests that the radiative transition probability diminishes under pressure. The intensity decay becomes strongly nonexponential in polymer matrices under compression.