Weak Emitter Research Articles

Resonant Plasmonic Enhancement of Single-Molecule Fluorescence by Individual Gold Nanorods

Enhancing the fluorescence of a weak emitter is important to further extend the reach of single-molecule fluorescence imaging to many unexplored systems. Here we study fluorescence enhancement by isolated gold nanorods and explore the role of the surface plasmon resonance (SPR) on the observed enhancements. Gold nanorods can be cheaply synthesized in large volumes, yet we find similar fluorescence enhancements as literature reports on lithographically fabricated nanoparticle assemblies. The fluorescence of a weak emitter, crystal violet, can be enhanced more than 1000-fold by a single nanorod with its SPR at 629 nm excited at 633 nm. This strong enhancement results from both an excitation rate enhancement of ∼130 and an effective emission enhancement of ∼9. The fluorescence enhancement, however, decreases sharply when the SPR wavelength moves away from the excitation laser wavelength or when the SPR has only a partial overlap with the emission spectrum of the fluorophore. The reported measurements of fluorescence enhancement by 11 nanorods with varying SPR wavelengths are consistent with numerical simulations.

A stable and strongly luminescent dinuclear Cu(i) helical complex prepared from 2-diphenylphosphino-6-methylpyridine

Treatment of 2-diphenylphosphino-6-methylpyridine (dpPyMe) with Cu(CH(3)CN)(4)BF(4) afforded the stable dinuclear Cu(I) complex [Cu(2)(μ-dpPyMe)(3)(CH(3)CN)](BF(4))(2). This compound is a weak emitter in solution, however a remarkably high emission quantum yield (46%) has been found in a rigid matrix at room temperature.

Donor–acceptor type silole compounds with aggregation-induced deep-red emission enhancement: synthesis and application for significant intensification of near-infrared photoluminescence

Through efficient Förster resonance energy transfer, the near-infrared emission (850 nm) of a guest (weak near-infrared emitter)-host (strong deep-red emitter) system is greatly enhanced by excitation of the host molecule at 508 nm, in comparison with excitation of the guest molecule at 660 nm.

Crystallization-Induced Emission Enhancement in a Phosphorus-Containing Heterocyclic Luminogen

Whereas aggregation often quenches luminescence, the emission of a heterocyclic luminogen, 10-[2,5-bis(4-pentyloxyphenylcarbonyloxy)phenyl]-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (3), is greatly enhanced by aggregate formation. Crystallization further boosts the emission of 3, turning it from a weak emitter in the solution state to a strong emitter in the crystalline state. The emission of 3 is changed in response to the exposure to vapors of volatile organic compounds (VOCs). The morphology of the thin film of 3 is reversibly and repeatedly modulated between amorphous and crystalline phases by simple fuming-heating and heating-cooling cycles, leading to an emission switching between bright and dark states. The novel attributes of the crystallization-induced emission enhancement, the VOC-responsive emission change, and the morphology-tunable emission switching of 3 could enable it to find applications in an array of technological areas, including chemosensing, optical display, and rewritable information storage.

RESULTS OF THE FIRST SIMULTANEOUS X-RAY, OPTICAL, AND RADIO CAMPAIGN ON THE BLAZAR PKS 1622-297

Coordinated X-ray, optical, and radio observations of the blazar PKS 1622-297 were obtained during a three-week campaign in 2006 using the Rossi X-Ray Timing Explorer (RXTE), the University of Michigan Radio Astronomy Observatory, and optical telescopes at Cerro Tololo Inter-American Observatory. The RXTE observations indicate that this object is a comparatively weak X-ray emitter for a Flat-Spectrum Radio Quasar. The observed broadband spectral shape indicates that X-rays were most likely produced by the Inverse Compton processes. Optical observations of this object produced unexpected results in that this object appeared redder when in a bright state and bluer when in a faint state, contrary to the observed behavior of BL Lac objects.

Effects of Steric Constraint on Chromium(III) Complexes of Tetraazamacrocycles, 2. Comparison of the Chemistry and Photobehavior of the trans-Dichloro- and trans-Dicyano- Complexes of Cyclam, 1,4-C2-Cyclam, and 1,11-C3-Cyclam

The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,11-C3-cyclam (1,4,8,11-tetraazabicyclo[9.3.3]heptadecane) is reported. Only trans complexes are formed, and the structure of trans-[Cr(1,11-C3-cyclam)Cl2]PF6 is presented. The chemical and photophysical behavior of the 1,11-C3-cyclam complexes are compared with those of the corresponding cyclam (1,4,8,11 tetraazacyclotetradecane) and 1,4-C2-cyclam (1,4,8,11-tetraazabicyclo[10.2.2]hexadecane) complexes. The aquation rate of trans-[Cr(1,11-C3-cyclam)Cl2]+ is similar to that of the corresponding 1,4-C2-cyclam complex and is more than 5 orders of magnitude faster than the cyclam counterpart. A monotonic increase in the extinction coefficient is observed on going from the cyclam complexes to the 1,11-C3-cyclam complexes to the 1,4-C2-cyclam complexes, and this is related to the degree of centrosymmetry in each complex. The trans-[Cr(1,11-C3-cyclam)(CN)2]+ complex is a weak emitter in aqueous solution with a room-temperature emission maximum at 724 nm (tau=23 micros). Like the corresponding 1,4-C2-cyclam complex (tau=0.24 micros), the 1,11-C3-cyclam complex shows no deuterium-isotope effect in room-temperature solution. This is in marked contrast to the corresponding cyclam complex which has an emission lifetime of 335 micros and a significant deuterium isotope effect in room-temperature solution. Low temperature (77K) data are also presented in an attempt to understand the differences in photophysical behavior.

Biogenic Volatile Organic Compounds (BVOCs) emissions from Abies alba in a French forest

Air quality studies need to be based on accurate and reliable data, particularly in the field of the emissions. Biogenic emissions from forests, crops, and grasslands are now considered as major compounds in photochemical processes. Unfortunately, depending on the type of vegetation, these emissions are not so often reliably defined. As an example, although the silver fir ( Abies alba) is a very widespread conifer tree in the French and European areas, its standard emission rate is not available in the literature. This study investigates the isoprene and monoterpenes emission from A. alba in France measured during the fieldwork organised in the Fossé Rhénan, from May to June 2003. A dynamic cuvette method was used. Limonene was the predominant monoterpene emitted, followed by camphene, α-pinene and eucalyptol. No isoprene emission was detected. The four monoterpenes measured showed different behaviours according to micrometeorological conditions. In fact, emissions of limonene, α-pinene and camphene were temperature-dependant while eucalyptol emissions were temperature and light dependant. Biogenic volatile organic compounds emissions were modeled using information gathered during the field study. Emissions of the three monoterpenes previously quoted were achieved using the monoterpenes algorithm developed by Tingey et al. (1980) [Tingey D, Manning M, Grothaus L, Burns W. Influence of light and temperature on monoterpene emission rates from slash pine. Plant Physiol 1980;65: 797–801.] and the isoprene algorithm [Guenther, A., Monson, R., Fall, R., 1991. Isoprene and monoterpene emission rate variability: observations with eucalyptus and emission rate algorithm development. J Geophys Res 26A: 10799–10808.]; [Guenther, A., Zimmerman, P., Harley, P., Monson, R., Fall, R., 1993. Isoprene and monoterpene emission rate variability: model evaluation and sensitivity analysis. J Geophys Res 98D: 12609–12617.]) was used for the eucalyptol emission. With these methods, simulation results and observations agreed fairly well. The standard emission rate (303 K) and β-coefficient averaged for limonene, camphene and α-pinene were respectively of 0.63 μg g dw −1 h −1 and 0.06 K −1. For eucalyptol, the standard emission rate ( T=303 K and PAR=1000 μmol m −2 s −1) was 0.26 μg g dw −1 h −1. This classified A. alba as a weak monoterpenes emitter.

Surface Recombination Currents in “Type-II” NpN InP–GaAsSb–InP Self-Aligned DHBTs

Surface recombination effects are studied in non-passivated non-self-aligned and self-aligned NpN InP-GaAsSb-InP double heterostructure bipolar transistors (DHBTs) down to submicrometer emitter dimensions, and over current densities ranging from 10 A/cm/sup 2/ to 100 kA/cm/sup 2/. The present study is motivated by the drive to scale InP DHBTs for higher speeds and integration densities. Self-aligned InP-GaAsSb-InP DHBTs are characterized by weak emitter size effects (ESEs), and periphery recombination currents are found to be very nearly identical to published results for InP-GaInAs SHBTs despite the major differences in emitter junction band alignments ("type-II" versus "type-I") and injection mechanisms (thermal versus hot electron injection). The correspondence of measured periphery currents in both systems indicates that ESEs are dominated by a mechanism common to InP-GaAsSb and InP-GaInAs devices: this requirement is fulfilled by the direct electron injection from the InP emitter mesa sidewalls onto the extrinsic base surface. Consideration of band alignments and surface depletion effects at the extrinsic base surface is used to explain the commonality of emitter size effects in InP-GaAsSb and InP-GaInAs devices.

Monoterpene emissions from Beech (Fagus sylvatica) in a French forest and impact on secondary pollutants formation at regional scale

Abstract Biogenic emissions from forest, crops, and grasslands are now considered major compounds in photochemical processes. Air quality analyses require more and more accurate input data, particularly emissions. Unfortunately, depending on the type of vegetation, these emissions are not always reliably defined. For example, Fagus sylvatica , which is a very abundant deciduous tree in France and in Europe, is a weak monoterpene emitter in the European inventory developed by Simpson et al. [1999. Journal of Geophysical Research 104, 8113–8152], but is a strong monoterpene emitter in Luchetta [1999. Caracterisation et quantification dans la basse atmosphere de composes organiques volatils biogeniques et anthropiques contribuant a la pollution de l’air. Ph.D. thesis, INPT Toulouse]. Beech ( F. sylvatica ) emission potential has never been measured in France. This study investigates the isoprene and monoterpenes emission measurements from F. sylvatica in France during a research program INTERREG III in Fosse Rhenan, during May and June 2003. A dynamic cuvette method was used. Sabinene is the main monoterpene emitted, composing more than 90% of biogenic emissions. The remaining is composed of α -pinene, β -pinene and limonene. No isoprene emissions were detected. The monoterpene emissions from F. sylvatica are affected by temperature and photosynthetic active radiation (PAR). In order to describe monoterpene emissions, the “isoprene algorithm” developed by Guenther et al. [1991. Journal of Geophysical Research 26A, 10799–10808; 1993. Journal of Geophysical Research 98D, 12609–12617] has been used. With this algorithm, simulation results and observations agree fairly well. The standard emission rate ( T = 303 K and PAR=1000 μmol m −2 s −1 ) for total monoterpenes is 43.5 μg g dw −1 h −1 . This classifies F. sylvatica as a strong monoterpene emitter. The European inventory [Simpson, et al., 1999. Journal of Geophysical Research 104, 8113–8152], which is the standard inventory of the model CHIMERE, is adjusted using this value. This induces an annual increase of 30% in simulated monoterpene emissions in France. These two inventories are used to simulate a regional pollution event during spring 2003. No significant differences are observed for ozone concentrations. Peroxy Acyl Nitrate (PANs) and formaldehyde concentrations increase by up to 10% in the adjusted inventory.

Study and development of a silicon infrared diode operating under forward bias

This work presents an advance in optoelectronic silicon-based devices, since a theoretical and experimental study by the authors of an inexpensive transformation process by which a commercially available silicon p–n junction has been made to emit infrared light. The authors introduce a ‘nano-layer’ degradation to aid in the recombination processes necessary to obtain a silicon light emitting process. Silicon diodes are known as a very weak light emitter or even no-light emitting devices. Several techniques have been used to force silicon to emit light, the results was light emission in all colors, varying from visible to infrared. But the efficiency of the device remains very low compared to the costs of fabrication. In our paper, the intensity of the emitted light is an increasing function of the injected current, instead of the attenuation reported by others.

Structural control of the excited-state dynamics of bis(dipyrrinato)zinc complexes: self-assembling chromophores for light-harvesting architectures.

The replacement of the phenyl rings at the 5,5'-positions of a bis(dipyrrinato)zinc complex with mesityl groups transforms the molecule from a very weak emitter that deactivates rapidly after photoexcitation (Phif = 0.006; tau approximately 90 ps) to a highly fluorescent chromophore with a long-lived singlet excited state (Phif = 0.36; tau approximately 3 ns). The results demonstrate that steric constraints on aryl-ring internal rotation dramatically alter the excited-state properties of 5,5'-substituted bis(dipyrrinato)metal complexes. The insights establish the foundation for tuning the photophysical properties of these chromophores for use in diverse photochemical applications.

Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles. Chemistry and excited-state behavior of 1,4-C2-cyclam complexes.

The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,4-C(2)-cyclam = 1,4,8,11-tetraazabicyclo[10.2.2]hexadecane is reported. The ligand appears to form only trans complexes, and the structure of trans-[Cr(1,4-C(2)-cyclam)Cl(2)]PF(6) is presented. The constraint imposed by the additional C(2) linkage distorts the bond angles significantly away from the ideal values of 90 and 180 degrees. The effect of the distortion is to enhance the aquation rate of trans-[Cr(1,4-C(2)-cyclam)Cl(2)](+) (k(obs) for trans-[Cr(1,4-C(2)-cyclam)(H(2)O)(2)](3+) formation = 6.5 x 10(-)(2) s(-)(1), 0.01M HNO(3), 25 degrees C) by over 5 orders of magnitude relative to trans-[Cr(cyclam)Cl(2)](+). The complexes trans-[Cr(1,4-C(2)-cyclam)Cl(2)](+) and trans-[Cr(1,4-C(2)-cyclam)(CN)(2)](+) are found to have extinction coefficients four to five times higher than their cyclam analogues, owed to the lack of centrosymmetry caused by the steric constraint. The trans-[Cr(1,4-C(2)-cyclam)(CN)(2)](+) complex is a very weak emitter in aqueous solution with a broad room-temperature emission centered at 735 nm (tau = 0.24 micros). Extended photolysis (350 nm, 15 h) of trans-[Cr(1,4-C(2)-cyclam)(CN)(2)](+) in aqueous solution results in CN(-) ligand loss. This is in stark contrast to its unconstrained cyclam analogue, which is photoinert and has a room-temperature emission lifetime of 335 micros.

Synthesis, spectroscopic properties and proton-coupled redox activities of mononuclear osmium(II) mixed-chelates derived from pyrazole-3,5-bis(benzimidazole) and 2,2′-bipyridine

The mixed-ligand osmium(II) complexes [(bpy) 2Os(H 3pzbzim)](ClO 4) 2·2H 2O ( 1) and [(bpy) 2Os(Hpzbzim)]·2H 2O ( 2), where H 3pzbzim=pyrazole-3,5-bis(benzimidazole) and bpy=2,2′-bipyridine, have been synthesized and spectroscopically characterized. In complex ( 2), the NH deprotonation occurs at the pyrazole and at one of the metal-bound benzimidazole sites. As compared to complex ( 1), which undergoes reversible oxidation at 0.48 V (vs. Ag/AgCl) in acetonitrile, the redox potential of ( 2) is shifted to a much lower value, 0.14 V. The proton-coupled redox activities of the complexes have been studied over the pH range 1–12 in acetonitrile–water (3:2). From the pH versus E 1/2 profile, the equilibrium constants of the complex species in the protonated/deprotonated forms and the metal ion in +2/+3 oxidation states have been determined. The p K a values of the complexes in the +2 state have also been determined spectrophotometrically. The spectrophotometric titration of complex ( 1) with cerium(IV) has revealed the disappearance of the more intense and higher energy Os IIdπ→π*(bpy) MLCT band and the appearance of the less intense and lower energy π(H 3pzbzim)→Os IIIdπ LMCT band. The luminescence spectrum of ( 1) in methanol–ethanol at 77 K has shown it to be a weak emitter, while no emission is observed for ( 2).

Diffuse galactic gamma-ray continuum emission

Some of the most important questions about the diffuse gamma-ray continuum emission from the Galaxy are reviewed, based on Compton Observatory (CGRO) results, especially COMPTEL and EGRET, and also earlier COS-B analyses. The key issues include the role of emission from cosmic-ray interactions with molecular hydrogen and its energy dependence, emissivity gradients and their interpretation, the cosmic-ray electron spectrum and the effect of discrete sources. The relative contribution of the various emission processes at low and high latitudes is estimated and a plausible synthesis of the observed spectrum over 5 decades of energy is presented. In the energy range above 30 MeV, models based either on explicit cosmic-ray gradients or cosmic-ray/gas coupling can give acceptable fits to the data, and a clear distinction has yet to be made. The quality of the EGRET data may make this possible in the future. The value of the CO-to-H2 conversion factor from γ-rays is still uncertain and there is considerable evidence for cloud-to-cloud variations. The existence of a small emissivity gradient is well established, but is difficult to explain in a diffusive cosmic-ray propagation picture with sources distributed like SNR or pulsars unless there is a larger halo than suggested by cosmic-ray composition studies. In the energy range 1–30 MeV covered by COMPTEL the spectrum of the diffuse emission has been measured and is consistent with a combination of bremsstrahlung and inverse-Compton emission; spatial analysis shows strong evidence for a component with a wide latitude extent which is plausibly identified with the inverse-Compton component. The molecular hydrogen appears to be only a weak γ-ray emitter at low energies, which can be interpreted in terms of reduced MeV cosmic-ray electron density in molecular clouds. New data on the hard X-ray diffuse galactic emission is becoming available and indicates the need for a low-energy upturn in the electron spectrum or some other additional component. The contribution of unresolved sources to the ‘diffuse’ emission is unknown but-probably lies in the range 10–20%. At high latitudes the galactic emission is intense enough to significantly complicate the identification of the extragalactic component; in particular the inverse-Compton emission from a halo a few kpc in extent can account for much of the high-latitude galactic emission. The detection of the Large Magellanic Cloud and the non-detection of the Small Magellanic Cloud provide constraints on extragalactic cosmic-rays, and provide an interesting comparison with the properties of the galactic system. On account of the large amount of data from CGRO now available, this is a subject in rapid development, and this paper provides a snapshot of the situation around mid-1995.

Structure, physical, chemical and photophysical properties of Pt(bph) (CO) 2, where bph is the biphenyl dianion

The complex Pt(bph) (CO) 2 crystallizes in the space group Cmcm with a = 18.647(6), b = 9.566(2) and c = 6.4060(5) A ̊ . The geometry of the molecule is slightly distorted from square planar with a PtC(CO) bond distance of 1.98(2) Å and a PtC(bph) bond distance of 2.04(2) Å. The Pt(bph)(CO) 2 complex serves as a precursor for the preparation of a wide variety of Pt(bph)X 2 complexes, where X = monodentate ligands such as acetonitrile, pyridine, etc., and X 2 = bidentate ligands such as bypyridine, 1,10-phenanthroline, etc. In the solid state, the complex exhibits a green color, but when ground with an alkali metal salt turns deep blue to purple. In CH 2Cl 2, the color disappears but optical transitions are observed at 271 nm (2.7 × 10 4 M −1 cm −1), 303 nm (1.1 × 10 4 M −1 cm −1) and 330 nm (5.5 × 10 3 M −1 cm −1). The complex is a weak emitter exhibiting a structured spectrum in CH 2Cl 2 at r.t. with maxima located at 562 and 594 nm and an emission lifetime of 3.1 μs when excited at 337 nm.

Warm ionized gas in the edge-on galaxies NGC 4565 and NGC 4631

We present H-alpha observations of two edge-on galaxies: NGC 4565 and NGC 4631. In contrast to NGC 891, which was studied in a previous paper, neither of these galaxies shows evidence for a smooth, vertically extended, diffuse, warm ionized medium. NGC 4565 is a weak H-alpha emitter, and shows no evidence for a chimney mode in its disk. It is most likely that its young associations do not contain the numbers of OB stars necessary to create superbubbles and chimneys and power a significant halo. NGC 4631 is a strong H-alpha emitter, and shows evidence of disturbances in its distribution of H-alpha emission, presumably due to recent encounters with its companions. The lack of a significant diffuse H-alpha halo may be due to a hot, unconfined wind from the disk. Although NGC 4631 does not show classic wormlike structures as in NGC 891, there is patchy high-z emission in abundance, and a few faint high-z loops, which are probably the result of star-formation activity in the disk. We discuss the implications of our results on NGC 891, NGC 4565, and NGC 4631 for the disk-halo connection, in particular for the emerging connection between the galaxies' disk H-alpha emission and radio halo properties. Above the nuclear region of NGC 4631, there is a clear, vertical, double-worm structure, which we suggest is due to the breakout of a large superbubble created by an encounter-driven star formation event in the central regions. The structure coincides with a radio continuum feature seen at 2.7 GHz and possibly 8.1 GHz by Duric, Crane, and Seaquist. This nuclear star formation activity is probably a scaled-down version of similar activity in NGC 3079, M82, and NGC 253.

Cyclodextrin-induced room-temperature phosphorescence of nitrogen heterocycles and bridged biphenyls

Cyclodextrin-enhanced room-temperature phosphorescence (CD-RTP) characteristics are reported for two- and three-ring nitrogen heterocycles and the bridged biphenyl heterocycles dibenzofuran, dibenzothiophene, and carbazole. The observation of CD-RTP is made possible by the proposed formation of a trimolecular inclusion complex composed of lumiphor, cyclodextrin, and an external heavy-atom species such as 1,2-dibromoethane. The nitrogen heterocycles exhibit phosphorescence in ..beta..-cyclodextrin which is characteristic of their unprotonated forms. Their CD-RTP is partially immune to quenching by molecular oxygen depending on the water solubility of the lumiphor. Biphenyl is a weak triplet state emitter in cyclodextrin, most probably due to stabilization of the ground-state, staggered conformation of the two aromatic rings. Bridged biphenyls, in which a five-member ring serves to induce planarity in the molecule, exhibit more intense CD-RTP than the parent compound. 25 references, 9 figures, 2 tables.

Fluorescence characteristics of kynurenine and N'-formylkynurenine. Their use as reporters of the environment of tryptophan 62 in hen egg-white lysozyme.

Several kynurenine derivatives including N'-formylkynurenine were prepared in high purity by the ozonization of the corresponding indole compounds. The fluorescence characteristics of those derivatives were examined in connection with the use of their fluorophores as reporters for the local environment of tryptophan in proteins. Kynurenine is a weak emitter of fluorescence, with an emission maximum at 480 nm on excitation at 365 nm. With decreasing solvent polarity, the fluorescence intensity increases logarithmically and the emission maximum shifts to blue. A linear relation between these fluorescence characteristics and solvent polarity exists when the polarity is shown in terms of dielectric constant. N'-Formylkynurenine is a somewhat stronger emitter of fluorescence than kynurenine. The emission maximum is 434 nm on excitation at 325 nm and it shifts to blue in solvents of low polarity. This blue shift is also linear with respect to the dielectric constant of the solvent. Other factors influencing kynurenine fluorescence and N'-formylkynurenine fluorescence examined were neighboring groups, ionic strength, temperature, and protein denaturants. Based on the results of the present investigation, the local environment of tryptophan 62 in hen egg-white lysozyme was examined using Kyn 62-lysozyme.

Monitoring intracellular transport

Ingested plastic scintillator spheres are shown to be a useful tool for investigating intracellular transport of material labelled by a weak beta emitter. It is found that-by numerically solving a linear integral equation with known kernel-the time evolution of the intracellular emitter density profile in the vicinity of the cell membrane is determinable from easily obtained experimental data. Applications to special biological systems are noted.

A Thin Film Optical Cavity to Induce Absorption or Thermal Emission

Several variations are given of a relatively simple thin film optical cavity construction which can be designed either to induce absorption in a weak absorber or to induce thermal emission from a weak emitter. In both cases the cavity is very selective with respect to polarization and wavelength.