Surface and confinement effects on the dielectric relaxation of a monohydroxy alcohol

2-ethyl-1-hexanol (2E1H) was confined to the surface of a collagen matrix at various concentration levels c. Dielectric spectroscopy revealed that upon decreasing c, the alcohol's prominent hydrogen-bond mediated Debye-like relaxation broadens and turns nonexponential. This destabilization of the supramolecular association is accompanied by an increasing relative strength of the structural relaxation in 2E1H up to a point beyond which the two processes are merged when the solvent molecules are sufficiently diluted. These results demonstrate that the contribution of the Debye-like relaxation can be completely suppressed and concomitantly the limit of a simple, nonassociating liquid is reached. Confinement of the alcohol in a monolithic glass with nanoscopic pores subjected to different internal surface treatments is also demonstrated to bear a large impact on the relative strengths of the two processes.     

Intramolecular perturbations and the quenching of luminescence in small molecules

We consider the problem of interpreting quenching kinetics in small molecules [e.g., CN, CH₂, NO₂ and SO₂] which show significant intrinsic interactions, and argue the importance of analyzing these data in terms of collisional transitions between perturbed (mixed electronic parentage) as opposed to pure (non-spectroscopic) vibronic states. Time resolved experiments are discussed which could determine more unambiguous deactivation cross sections and spectral assignments.     

Amplified luminescence quenching of phosphorescent metal-organic frameworks

Amplified luminescence quenching has been demonstrated in metal-organic frameworks (MOFs) composed of Ru(II)-bpy building blocks with long-lived, largely triplet metal-to-ligand charge-transfer excited states. Strong non-covalent interactions between the MOF surface and cationic quencher molecules coupled with rapid energy transfer through the MOF microcrystal facilitates amplified quenching with a 7000-fold enhancement of the Stern-V?lmer quenching constant for methylene blue compared to a model complex.     

Thermal quenching of characteristic luminescence. II

A model proposed earlier to explain the dependence of the quenching temperature (T_q) of a given luminescent center on the host lattice is extended to luminescent centers bearing a formally effective charge. Predictions from this model are compared with experimental data. The agreement is satisfactory. It turns out that effectively charged centers with charge-transfer excitation (e.g., Eu³⁺, WO^2?₄) do not have a high value of T_q, whereas those with Rydberg excitation (e.g., Tl⁺, Tb³⁺) can have a high value of T_q, especially if the host lattice is rigid.     

Structural and spectroscopic investigations on the quenching free luminescence of europium oxalate nanocrystals

The structural features leading to the intense quenching free luminescence exhibited by europium oxalate nanocrystals, poly[[hexaaquatri‐μ₂‐oxalato‐dieuropium] 4.34‐hydrate], {[Eu₂(C₂O₄)₃(H₂O)₆]·4.34H₂O}_n, is the focal point of this report. Europium oxalate nanocrystals were synthesized by a simple microwave‐assisted co‐precipitation method. Powder X‐ray diffraction analysis revealed the monoclinic structure of the nanocrystals and the phase purity. The morphology and particle size were examined by transmission electron microscopy (TEM) analysis. Luminescence measurements on a series of samples of La_2–xEu_x(C₂O₄)₃·10H₂O, with x varying in the range 0.1 to 2, established the quenching free nature exhibited by the europium oxalate nanocrystals. A single‐crystal structure analysis was carried out and the quenching free luminescence is explained on the basis of the crystal structure. A detailed photoluminescence characterization was carried out using excitation and emission studies, decay analysis, and CIE coordinate and colour purity evaluation. The various spectroscopic parameters were evaluated by Judd–Ofelt theoretical analysis and the results are discussed on the basis of the crystal structure analysis.     

Static and dynamic effects of confinement on self-diffusion

Expressions for second and fourth sum rules of velocity autocorrelation function have been derived for fluid confined to a rectangular nanotube. Expressions obtained for these sum rules involve density profiles which vary with distance from walls of the tube. These sum rules, incorporating the effect of static changes made due to confinement, and the model which involves dynamical effect have been coupled to study the self-diffusion coefficient. By considering model density profiles, it is found that the self-diffusion coefficient in a direction perpendicular to the wall behaves differently from that in a direction parallel to the wall. The perpendicular diffusion coefficient is found to be more strongly dependent on the width of the tube than the parallel diffusion. It is found that dynamical effects are more in the region that is near to the confining wall than the static effects which track density profile.     

Determination of the lifetime of singlet oxygen with the kinetics of quenching of its luminescence after a laser flash in films of amorphous polymers

Conclusions The lifetime of singlet oxygen is 22, 34, and 35 usec in polystyrene, polycarbonate, and polymethyl methacrylate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1484–1488, July, 1987.We would like to thank V. Ya. Shlyapintokh for his valuable comments in discussing the results.     

Microtiterplate phosphate assay based on luminescence quenching of a terbium complex amenable to decay time detection

We describe a terbium-ligand complex (TbL) for a microtiterplate assay for phosphate (P) in the 0.3-100 μmol L⁻¹ range based on luminescence quenching. As the pH optimum is at neutral pH (7.4) the probe is quenched by both, primary (H₂PO₄⁻) and secondary phosphate (HPO₄²⁻). The LOD is 110 nmol L⁻¹. A Stern-Volmer study revealed that quenching is mostly static. Due to the ms-decay time of TbL, the first luminescence lifetime assay for phosphate could also be developed. The lifetime-based calibration plot is linear between 0.5 and 5 μmol L⁻¹ of P. The effect of various surfactants on assay performance and a study on interferents are presented. The probe was successfully applied to determination of P in commercial plant fertilizers and validated against the molybdenum blue test. The probe is the most sensitive lanthanide-based probe for phosphate.     

Regiodependent luminescence quenching of biotinylated N-sulfonyl-acridinium-9-carboxamides by avidin

[reaction: see text] Biotin was conjugated to chemiluminescent N-sulfonylacridinium-9-carboxamides at the N-10 or 9-position carboxamide. Upon binding to avidin, the light output of the N-10 derivative (8) was quenched up to 92% upon triggering with basic peroxide, while the 9-position carboxamide conjugate (9) was quenched only 33%. The utility of this effect was demonstrated in a model homogeneous chemiluminescence assay.     

Electronic confinement effects on the reaction field type calculations of solvent effects

We analyze some procedures to introduce the effect of confining the electrons of the hydrogen atoms in cavitation spheres like those used in the self‐consistent reaction field models for studying the solvent influence on molecular properties [as polarizable continuum model (PCM), or conductor screening model (COSMO)]. We have found that the boundary conditions to be applied have an important effect on the system energy that by no means should be neglected in this type of calculations. We have found as well that “‐nG” expansion technique could be applicable in this kind of calculations (even at the very simple “‐3G” level) and lead us to a relatively simple form of applying the theory. Moreover, we have found a way to define the cavitation radius of PCM calculations, by minimizing the system energy with respect to this parameter, which could be a more satisfactory procedure—at least from a theoretical point of view—than the use of empirical values characteristic of most of the PCM or COSMO standard calculations. © 2013 Wiley Periodicals, Inc.     

Rapid exchange luminescence: nitroxide quenching and implications for sensor applications

The quenching of terbium emission in the sensitized complex Tb3+-cs124-DTPA by nitroxide radical TEMPO derivatives in aqueous solutions has been studied with time-averaged and time-resolved methods. The time-resolved results show more quenching than the time-averaged values, opposite to the behavior expected for static quenching. A rapid exchange model with a slightly fluorescent fluorophore/quencher complex is proposed. Due to the long time scale of Tb3+ emission, dynamical averaging must be considered in the interpretation of experiments. The rapid exchange limit is shown to be consistent with the present results. The utility of these observations in the design of sensors that are not limited by a background level is noted.     

Solvent and temperature effects on positronium annihilation parameters and on its quenching reactions with the free radical HTEMPO

Positron annihilation lifetime spectroscopy (LS) and the Doppler broadening of the annihilation radiation lineshape (DBARL) technique have been used in conjunction to study solvent and temperature effects on both the positronium (Ps) quenching reactions with the free-radical HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl) and the annihilation parameters. A change in the nature of the quenching reaction is observed from spin conversion in benzene (Bz),N,N-dimethylacetamide (NDMA), andN-methylformamide (NMFA) to Ps oxidation inmeta cresol (m-C); it is attributed to a modification of the electron density distribution in the quenching molecule due to hydrogen bonding with them-C molecules. The data also indicate that the full-width at half-maximum of the momentum distribution associated to para-positronium (p-Ps) resulting from the spin conversion reaction is smaller by a factor of 2 than that forp-Ps directly formed in the positron spur. The ortho-positronium (o-Ps) pickoff lifetime and momentum distribution are shown to give access to physicochemical and structural properties of the solvents.     

Chiroptical properties of an optically pure dicopper(I) trefoil knot and its enantioselectivity in luminescence quenching reactions

Chiroptical spectroscopy is used to investigate the properties of an optically pure dinuclear copper(I) trefoil knot. For the metal-to-ligand charge tranfer (MLCT) transition in the visible region (520 nm), the electric and magnetic transition dipole moments are determined from absorption and circular dichroism spectra: 2.8 Debye and 0.5 Bohr magneton (muB). Circular polarization in the luminescence (CPL) of the knot is determined and this allows the electric and magnetic transition dipole moments in emission to be calculated: 0.02 Debye and 0.003 muB. The large difference between the moments in absorption and emission shows that the emission observed does not originate directly from the 1MLCT state. Given the low probability for radiative decay we assign the long-lived emitting excited state to a 3MLCT state. The copper(I) trefoil knot is found to quench the emission from TbIII and EuIII(dpa)3(3)-(dpa = pyridine-2,6-dicarboxylate) with a bimolecular rate constant of 3.2 and 3.3 x 10(7)M(-1)S(-1), respectively, at room temperature in water-acetonitrile (1:1 by volume). Experimental results indicate that the (lambda)-knot preferentially quenches the lambda enantiomer of the lanthanide complex with an enantioselectivity (ratio of quenching rate constants for lambda and lambda: kqlambda/kqdelta) of 1.012+/-0.002 for EuIII and 1.0180+/-0.003 for TbIII.     

Reversible surface oxidation and efficient luminescence quenching in semiconductor single-wall carbon nanotubes

We have investigated reversible single-wall carbon nanotube (SWNT) oxidation by quantitative analysis of the oxide-induced absorption bleaching and luminescence quenching at low pH. These data, in combination with DFT structure calculations, suggest that the nanotube oxide is a 1,4-endoperoxide. At low pH, the endoperoxide protonates to create a hydroperoxide carbocation, introducing a hole in the SWNT valence band. Nanotube luminescence is extremely sensitive to quenching by hole-doping, while the absorption is relatively robust.     

Size Effects on the Luminescence Properties of Polymer Nanowires简

Poly（3-（2-methoxyphenyl）thiophene） （PMP-Th） nanowires were fabricated using porous anodic alumina （PAA） as template through electrochemical polymerization by cyclic voltammetry. The control on the size of nanowires was confirmed by electron microscopy. The results indicated that the luminescence spectra of PMP-Th nanowires in PAA nanochannels were blue-shifted and emission intensity was enhanced compared to the emission of the PMP-Th film. Moreover, the luminescent spectra of PMP-Th nanowires were size dependent, which may result from the change in the degree of confinement of nanowires in PAA. F6rster energy transfer from PAA to PMP-Th molecules is considered to be responsible for the enhancement of luminescence from PMP-Th nanowires in PAA. The results show that the emission properties of polymers with nanostructures can be tuned by controlling their size.     

Theoretical explanation of the quenching of luminescence in cerium‐doped ytterbium oxyorthosilicate

A remarkable result in applied solid‐state physics is that whereas Ce‐doped yttrium oxyorthosilicate, Y₂(SiO₄)O:Ce, is an excellent scintillator, the related Ce‐doped ytterbium oxyorthosilicate, Yb₂(SiO₄)O:Ce, does not scintillate at all at room temperature. These compounds, Y and Yb, besides possessing the same crystal structure, both are trivalent and yield almost identical ionic radii. In order to understand the difference between the luminescent properties of these materials, we have performed an ab initio calculation to investigate the charge‐transfer mechanism involving their first excited states. By using a representative cluster model, a crossing is found between the ground and the excited state of the ytterbium compound, though not so in the yttrium compound. This suggests that in the solid state, the luminiscence quenching can occur via a nonradiative transition, although luminescence at low temperature might thus be feasible. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 198–203, 2000     

A microscopic theory of nonlinear luminescence quenching at high levels of pumping

A microscopic theory of the exciton annihilation based on the superposition approximation for a three-particle density matrix is proposed. A new effect of the enhancement of luminescence quenching is predicted for excitons with the dispersion law close to one- or two-dimensional.     

Static luminescence quenching by oxygen and nitric oxide for phenanthrene in glassy matrices

Steady-state and pulsed methods have been applied to static phosphorescence and fluorescence quenching for phenanthrene caused by oxygen and nitric oxide. The characteristic fluorescence quenching distances have been determined for oxygen (8.7±0.5 Å) and nitric oxide (8.9±0,5 Å); the phosphorescence quenching involves an exchange mechanism, and measurements have been made on the characteristic quenching distances R₀ and exchange-interaction attenuation parameters L. Estimates have been made on the rate constants for dynamic quenching of the triplet excited states of phenanthrene in low-viscosity liquids, which agree well with the measured values for hexane.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 667–672, November–December, 1988.     

Lanthanide luminescence quenching as a detection method in ion chromatography. Chromate in surface and drinking water

Dynamic quenching of Eu(III) and Tb(III) luminescence by inorganic anions as a detection method in ion chromatography was investigated. To obtain a high luminescence intensity, lanthanide(III) complexes are formed with ligands which make indirect excitation of the ions possible. Only a few anions (e.g., nitrite, chromate) induce efficient dynamic luminescence quenching. Chromate is an efficient quencher of Tb-acac luminescence. Samples of tap water and surface water, spiked with chromate, were injected into a high-performance liquid chromatographic system with post-column addition of the luminescent complex. In this way, a detection limit of 1.1 . 10(-7) M (13 ppb) of chromate could be obtained.