Emission Rate Constants Research Articles

Bright and long-lasting aqueous peroxyoxalate chemiluminescence in cellulose microspheres.

Water decreases the brightness of the peroxyoxalate chemiluminescence partially due to the hydrolysis of the oxalate reagent. Here, we show that encapsulation of an oxalate ester and the fluorescent activator in microspheres of cellulose esters increases the emission intensity 30 times compared to the same reaction in water without encapsulation, whereas the emission intensity decay rate constants are considerably lower. Emission intensities, rate constants and chemiluminescence quantum yields increase with increasing hydrogen peroxide concentrations. These results expand the potential of application of chemiluminescence, contributing for the development of ultrasensitive analytical methods.

Charge Transfer-Promoted Excited State of a Heavy-Atom-Free Photosensitizer for Efficient Application of Mitochondria-Targeted Fluorescence Imaging and Hypoxia Photodynamic Therapy.

Conventional photosensitizers (PSs) used in photodynamic therapy (PDT) have shown preliminary success; however, they are often associated with several limitations including potential dark toxicity in healthy tissues, limited efficacy under acidic and hypoxic conditions, suboptimal fluorescence imaging capabilities, and nonspecific targeting during treatment. In response to these challenges, we developed a heavy-atom-free PS, denoted as Cz-SB, by incorporating ethyl carbazole into a thiophene-fused BODIPY core. A comprehensive investigation into the photophysical properties of Cz-SB was conducted through a synergistic approach involving experimental and computational investigations. The enhancement of intersystem crossing (kISC) and fluorescence emission (kfl) rate constants was achieved through a donor-acceptor pair-mediated charge transfer mechanism. Consequently, Cz-SB demonstrated remarkable efficiency in generating reactive oxygen species (ROS) under acidic and low-oxygen conditions, making it particularly effective for hypoxic cancer PDT. Furthermore, Cz-SB exhibited good biocompatibility, fluorescence imaging capabilities, and a high degree of localization within the mitochondria of living cells. We posit that Cz-SB holds substantial prospects as a versatile PS with innovative molecular design, representing a potential "one-for-all" solution in the realm of cancer phototheranostics.

A Quantitative Method to Measure the Kinetics of Elemental Mercury Emissions From Black Shale (Nova Scotia, Canada).

A controlled chamber method using continuous gold trap atomic fluorescence spectroscopy (AFS) (Tekran 2537X) for the analysis of Hg(0) emissions from moderate mass rock samples was developed and tested. A series of black shale and other bedrock samples from Nova Scotia, Canada, were used to test the method and its reproducibility. Hg(0) emissions at 170°C were measured to quantify both free surficial Hg(0) and Hg(0) that had penetrated the rock structure. High volumes of chamber air (45 L) were sampled using 30min collection times to achieve detectable elemental mercury (Hg(0)) emissions. We found higher percentage masses of Hg(0) were released (1.1%-4.1% of total Hg mass present) in black shale samples as compared to granite and basalt samples from the same region (0.0%-0.3% released) over 350h of continuous analysis time. The pseudo first order emission rate constants ranged from 0.015-0.245h-1 (mean 0.063h-1, standard deviation (SD) 0.102) for the black shale samples analyzed and was 0.004h-1 for the granite sample. The 24-h zero-order emission rate constants ranged between 0.41 and 3.54ngh-1 (mean 1.4ngh-1, SD 1.3) for the black shale samples analyzed and were ~ 0.01ngh-1 for the granite and basalt samples. This technique has useful implications for examining rock properties and Hg(0) emission rates.

Temperature Dependence of Fundamental Photophysical Properties of [Eu(MeOH-d4)9]3+ Solvates and [Eu·DOTA(MeOH-d4)]- Complexes.

The trivalent lanthanide ions show optical transitions between energy levels within the 4f shell. All these transitions are formally forbidden according to the quantum mechanical selection rules used in molecular photophysics. Nevertheless, highly luminescent complexes can be achieved, and terbium(III) and europium(III) ions are particularly efficient emitters. This report started when an apparent lack of data in the literature led us to revisit the fundamental photophysics of europium(III). The photophysical properties of two complexes-[Eu·DOTA(MeOH-d4)]- and [Eu(MeOH-d4)9]3+-were investigated in deuterated methanol at five different temperatures. Absorption spectra showed decreased absorbance as the temperature was increased. Luminescence spectra and time-resolved emission decay profiles showed a decrease in intensity and lifetime as the temperature was increased. Having corrected the emission spectra for the actual number of absorbed photons and differences in the non-radiative pathways, the relative emission probability was revealed. These were found to increase with increasing temperature. The transition probability for luminescence was shown to increase with temperature, while the transition probability for light absorption decreased. The changes in transition probabilities were correlated with a change in the symmetry of the absorber or emitter, with an average increase in symmetry lowering absorbance and access to more asymmetric structures increasing the emission rate constant. Determining luminescence quantum yields and the Einstein coefficient for spontaneous emission allowed us to conclude that lowering symmetry increases both. Furthermore, it was found that collisional self-quenching is an issue for lanthanide luminescence, when high concentrations are used. Finally, detailed analysis revealed results that show the so-called "Werts' method" for calculating radiative lifetimes and intrinsic quantum yields is based on assumptions that do not hold for the two systems investigated here. We conclude that we are lacking a good theoretical description of the intraconfigurational f-f transitions, and that there are still aspects of fundamental lanthanide photophysics to be explored.

Influence of thermal radiation on hot cluster decay rates and abundances

The influence of radiative cooling on the unimolecular decay rates of free, hot clusters and molecules with unspecified excitation energies is quantified. Two different regimes, defined by the magnitude of the energy of the photons emitted, are identified and the boundary between them is given. The boundary is determined in terms of the photon emission rate constants and thermal properties of the particles. Also the abundance spectra are calculated for the continuous cooling case, corresponding to small photon energies. The two regimes correspond to continuous cooling and single photon quenching of the unimolecular decay. The radiative effect can be parametrized by a redefinition of the time each individual cluster has available to undergo evaporation, expressed by an effective radiative time constant.

Radiative cooling of cationic carbon clusters, CN+, N = 8, 10, 13-16.

The radiative cooling of highly excited carbon cluster cations of sizes N = 8, 10, 13-16 has been studied in an electrostatic storage ring. The cooling rate constants vary with cluster size from a maximum at N = 8 of 2.6 × 104 s-1 and a minimum at N = 13 of 4.4 × 103 s-1. The high rates indicate that photon emission takes place from electronically excited ions, providing a strong stabilizing cooling of the molecules.

Phosphorescence Kinetics of Singlet Oxygen Produced by Photosensitization in Spherical Nanoparticles. Part I. Theory.

The singlet oxygen produced by energy transfer between an excited photosensitizer (pts) and ground-state oxygen molecules plays a key role in photodynamic therapy. Different nanocarrier systems are extensively studied to promote targeted pts delivery in a host body. The phosphorescence kinetics of the singlet oxygen produced by the short laser pulse photosensitization of pts inside nanoparticles is influenced by singlet oxygen diffusion from the particles to the surrounding medium. Two theoretical models are presented in this work: a more complex numerical one and a simple analytical one. Both the models predict the time course of singlet oxygen concentration inside and outside of the spherical particles following short-pulse excitation of pts. On the basis of the comparison of the numerical and analytical results, a semiempirical analytical formula is derived to calculate the characteristic diffusion time of singlet oxygen from the nanoparticles to the surrounding solvent. The phosphorescence intensity of singlet oxygen produced in pts-loaded nanocarrier systems can be calculated as a linear combination of the two concentrations (inside and outside the particles), taking the different phosphorescence emission rate constants into account.

Benzazasiline combined with triphenylborane-based cores for constructing deep-blue donor-acceptor-donor TADF emitters

We performed a first-principles systematic study on the fitness of two tricyclic donors (acridine and benzazasiline) interacting with five acceptors (triazine or triphenylborane-based) within the donor-acceptor-donor (D-A-D) framework for the potential application in organic light-emitting diodes (OLEDs) as thermally activated delayed fluorescence (TADF) emitters. Three types of compounds (D1-A-D1 (I), D2-A-D2 (II), and D1-A-D2 (III) were thus constructed to investigate the substitution pattern which can exhibit good TADF performance. We found that: by incorporating into the D-A-D frameworks and adopting an appropriate donor/acceptor combination, the studied compounds can bear rather small singlet-triplet gaps of ∼0.02 eV, and the emission energy can span a large space in (deep-)blue region (2.62∼3.13 eV); the molecular symmetry, in addition to the character of donors, control the properties of excited states, and acridine is more easily to be excited compared to benzazasiline. The symmetric setup (types I and II) is more suitable than asymmetric counterpart (type III) for optimal optoelectric properties. Accompanied with estimation of emission energy and rate constant, this study suggests that benzazasiline donor can serve as a versatile structural unit to combine with triphenylborane-based acceptor cores for constructing deep-blue D-A-D TADF emitters.

Rate constants for collision-induced emission of O2(a1Δg) with He, Ne, Ar, Kr, N2, CO2 and SF6 as collisional partners.

Rate constants for singlet oxygen collision induced emission of the a1Δg-X3Σ-g transition at 1.27 μm were measured for CO2, N2, SF6, and rare gases as collisional partners. Photolysis of ozone by 266 nm laser radiation produced singlet oxygen. We performed direct measurements of pressure dependences of the 1.27 μm emission intensity for partner gases. The measured rate constants kMa-X in the units of 10-24 cm3 s-1 are as follows: CO2 - 10 ± 2; N2 - 3.2 ± 0.6; SF6 - 7 ± 1; He - 1.1 ± 0.3; Ne - 1.3 ± 0.3; Ar - 2.8 ± 0.6; Kr - 6 ± 1. The measured values of kMa-X are close to the values calculated from absorption measurements. Considering the known rate constants kMb-a for the b1Σg+-a1Δg transition in the gas phase we found that the ratio kMa-X/kMb-a was constant and independent of a collisional partner according to the "spin-orbit based" mechanism of intensity borrowing proposed by Minaev (THEOCHEM, 1989, 183, 207). However, this ratio amounted to (1.3 ± 0.2) × 10-4, which is considerably lower than the theoretically predicted value of (3-6) × 10-4.

Models for nearly every occasion: Part III – One box decreasing emission models

ABSTRACTNew one box “well-mixed room” decreasing emission (DE) models are introduced that allow for local exhaust or local exhaust with filtered return, as well the recirculation of a filtered (or cleaned) portion of the general room ventilation. For each control device scenario, a steady state and transient model is presented.The transient equations predict the concentration at any time t after the application of a known mass of a volatile substance to a surface, and can be used to predict the task exposure profile, the average task exposure, as well as peak and short-term exposures. The steady state equations can be used to predict the “average concentration per application” that is reached whenever the substance is repeatedly applied. Whenever the beginning and end concentrations are expected to be zero (or near zero) the steady state equations can also be used to predict the average concentration for a single task with multiple applications during the task, or even a series of such tasks. The transient equations should be used whenever these criteria cannot be met.A structured calibration procedure is proposed that utilizes a mass balance approach. Depending upon the DE model selected, one or more calibration measurements are collected. Using rearranged versions of the steady state equations, estimates of the model variables—e.g., the mass of the substance applied during each application, local exhaust capture efficiency, and the various cleaning or filtration efficiencies—can be calculated. A new procedure is proposed for estimating the emission rate constant.

Control over the Emission Properties of [5]Helicenes Based on the Symmetry and Energy Levels of Their Molecular Orbitals.

The effect of different substituents on the fluorescence properties of [5]helicene derivatives was investigated in terms of molecular orbital symmetry. Unsubstituted [5]helicene is nonemissive due to the symmetry-forbidden S1 → S0 transition. However, the fluorescence emission rate constant (kf) of [5]helicenes is efficiently increased by removing the orbital degeneracy involved in the S1 → S0 transition. As a result, we achieved a [5]helicene derivative exhibiting a high fluorescence quantum yield (Φf = 0.23) and short emission lifetime (⟨τf⟩ = 1.5 ns), which is in marked contrast to unsubstituted [5]helicene (Φf = 0.04 and ⟨τf⟩ = 26 ns).

Gold Cluster Electronic Radiative Cooling and Abundances

The effect on abundances of radiative cooling of gold clusters is analyzed quantitatively for cluster sizes n = 8–20 based on known dissociation energies, radiative time constants and the monomer unimolecular decay frequency factor, and an assumed dimer loss frequency factor. Radiative cooling is observed to quench the temporal development of the abundance spectra and, in general, to produce larger size-to-size contrasts than observed in the absence of radiation. Also, the emission of photons with large and small energies was compared quantitatively. For small photon energies, the radiative time constant is not given by the photon emission rate constant. An alternative expression for this regime was found to be very accurate. Strong radiative cooling will have consequences both for the interpretation of mass abundance spectra and potentially also for the production of specific mass selected nanoparticles. The present work supplies the conceptual framework for such applications.

Factors that influence the spectroscopic properties of 1,3-bis[p-substituted-(phenylamino)]squaraines

The spectroscopic characteristics of a series of ten aminosquaraine dyes that differ in the type of chemical substituent at the p-position of the phenyl ring were investigated. The effect of solvent on the properties of the dyes in their ground and excited state is described. The absorption and emission properties, fluorescence lifetime and rate constants for radiative and non-radiative deactivation processes are also presented. The dyes displayed very short fluorescence lifetimes (about 3 ns) and dependence of the radiative deactivation process on the solvent viscosity.

Relaxation of vibrationally excited reaction products in a crystal lattice

The relaxation of vibrationally excited nitrogen molecules in the matrix of silver azide is studied. The effective rate constants for the interaction of an excited nitrogen molecule with free charge carriers (1.7 × 10–10 cm3 s–1) and for the generation a hole from the level of the produced defect at the expense of the vibrational energy of the molecule (3 × 1010 s–1) are estimated. An associative–dissociative mechanism of the deactivation is proposed, which consists in the capture of an electron onto the level of the produced defect with the subsequent emission of an electron into the conduction band at the expense of the vibrational energy of the excited molecule. The effective rate constants for electron emission from the excited level of a hydrogen-like defect at values of the principal quantum number of 3 and 4 are estimated as 1.8 × 109 and 2.8 × 109 s–1, respectively. Based on the processes considered, an expression for the probability of chain propagation is obtained.

Luminescence of the (O2(a(1)Δ(g)))2 collisional complex in the temperature range of 90-315 K: Experiment and theory.

Experimental and theoretical studies of collision induced emission of singlet oxygen molecules O2(a(1)Δg) in the visible range have been performed. The rate constants, half-widths, and position of peaks for the emission bands of the (O2(a(1)Δg))2 collisional complex centered around 634 nm (2) and 703 nm (3) have been measured in the temperature range of 90-315 K using a flow-tube apparatus that utilized a gas-liquid chemical singlet oxygen generator. The absolute values of the spontaneous emission rate constants k2 and k3 are found to be similar, with the k3/k2 ratio monotonically decreasing from 1.1 at 300 K to 0.96 at 90 K. k2 slowly decreases with decreasing temperature but a sharp increase in its values is measured below 100 K. The experimental results were rationalized in terms of ab initio calculations of the ground and excited potential energy and transition dipole moment surfaces of singlet electronic states of the (O2)2 dimole, which were utilized to compute rate constants k2 and k3 within a statistical model. The best theoretical results reproduced experimental rate constants with the accuracy of under 40% and correctly described the observed temperature dependence. The main contribution to emission process (2), which does not involve vibrational excitation of O2 molecules at the ground electronic level, comes from the spin- and symmetry-allowed 1(1)Ag←(1)B3u transition in the rectangular H configuration of the dimole. Alternatively, emission process (3), in which one of the monomers becomes vibrationally excited in the ground electronic state, is found to be predominantly due to the vibronically allowed 1(1)Ag←2(1)Ag transition induced by the asymmetric O-O stretch vibration in the collisional complex. The strong vibronic coupling between nearly degenerate excited singlet states of the dimole makes the intensities of vibronically and symmetry-allowed transitions comparable and hence the rate constants k2 and k3 close to one another.

Acclimation of isoprene emission and photosynthesis to growth temperature in hybrid aspen: resolving structural and physiological controls.

Acclimation of foliage to growth temperature involves both structural and physiological modifications, but the relative importance of these two mechanisms of acclimation is poorly known, especially for isoprene emission responses. We grew hybrid aspen (Populus tremula x P. tremuloides) under control (day/night temperature of 25/20 °C) and high temperature conditions (35/27 °C) to gain insight into the structural and physiological acclimation controls. Growth at high temperature resulted in larger and thinner leaves with smaller and more densely packed chloroplasts and with lower leaf dry mass per area (MA). High growth temperature also led to lower photosynthetic and respiration rates, isoprene emission rate and leaf pigment content and isoprene substrate dimethylallyl diphosphate pool size per unit area, but to greater stomatal conductance. However, all physiological characteristics were similar when expressed per unit dry mass, indicating that the area-based differences were primarily driven by MA. Acclimation to high temperature further increased heat stability of photosynthesis and increased activation energies for isoprene emission and isoprene synthase rate constant. This study demonstrates that temperature acclimation of photosynthetic and isoprene emission characteristics per unit leaf area were primarily driven by structural modifications, and we argue that future studies investigating acclimation to growth temperature must consider structural modifications.

승용차 냉방장치로부터의 온실가스 냉매인 HFC-134a 탈루배출모델에 대한 연구

The objective of this research was to develop fugitive emission models of HFC-134a (Hydrofluorocarbon-134a) at the operation and disposal stages of passenger cars. It is essential to estimate the emission of HFC-134a from mobile air conditioner (MAC) due to its high Global Warming Potential (GWP) and extensive use as a refrigerant in MAC. The first-order emission model was introduced and the emission rate constant was assumed to be unvaried with time. A commercial recovery station of refrigerants was used to recover the HFC-134a from the MAC. Average emission rate constant and annual emission rate during the operation period of vehicle are estimated to be <TEX>$0.0538{\pm}0.0092$</TEX> (n=21) <TEX>$yr^{-1}$</TEX> and <TEX>$5.2{\pm}0.6%$</TEX>, respectively within a confidence interval of 95%. According to the model results, about 50% of HFC-134a would be emitted from the MAC during the 10 years operation of passenger cars. On the other hand, average remaining portion of HFC-134a in the MACs of scrap cars is <TEX>$58.2{\pm}4.8%$</TEX> (n=50) within a confidence interval of 95%, suggesting that over 40% of the initially charged amount could be released fugitively after disposal provided that the HFC-134a would not be properly treated or recycled.

Direct estimation of functional PSII reaction center concentration and PSII electron flux on a volume basis: a new approach to the analysis of Fast Repetition Rate fluorometry (FRRf) data

Phytoplankton primary productivity is most commonly measured by 14C assimilation although less direct methods, such as O2 exchange, have also been employed. These methods are invasive, requiring bottle incubation for up to 24 h. As an alternative, Fast Repetition Rate fluorometry (FRRf) has been used, on wide temporal and spatial scales within aquatic systems, to estimate photosystem II (PSII) electron flux per unit volume (JVPSII), which generally correlates well with photosynthetic O2 evolution. A major limitation of using FRRf arises from the need to employ an independent method to determine the concentration of functional photosystem II reaction centers ([RCII]); a requirement that has prevented FRR fluorometers being used, as stand‐alone instruments, for the estimation of electron transport. Within this study, we have taken a new approach to the analysis of FRRf data, based on a simple hypothesis; that under a given set of environmental conditions, the ratio of rate constants for RCII fluorescence emission and photochemistry falls within a narrow range, for all groups of phytoplankton. We present a simple equation, derived from the established FRRf algorithm, for determining [RCII] from dark FRRf data alone. We also describe an entirely new algorithm for estimating JVPSII, which does not require determination of [RCII] and is valid for a heterogeneous model of connectivity among RCIIs. Empirical supporting evidence is presented. These data are derived from FRR measurements across a diverse range of microalgae, in parallel with independent measurements of [RCII]. Possible sources of error, particularly under nutrient stress conditions, are discussed.

Self‐Assembly and Aggregate‐Induced Enhanced Emission of Amphiphilic Fluorescence Dyes in Water and in the Solid State

1-Cyano-1,2-bis(biphenyl)ethene (CNBE) derivatives with a hexa(ethylene glycol) group as an amphiphilic side chain were synthesized and the self-assembling character and fluorescence behavior were investigated. The amphiphilic derivatives showed aggregate-induced enhanced emission (AIEE) in water and in the solid state. The fluorescence quantum yield increased as the rigidity of the aggregates increased (i.e., in ethyl acetate<in water<in the solid state). As determined from measurements of fluorescence spectra, fluorescence quantum yields, and fluorescence lifetimes, a key factor for the enhanced emission is suppression of the nonradiative decay process arising from restricted molecular motion. Additionally, the difference in the emission rate constant is not negligible and can be used to interpret the difference in fluorescence quantum yield in water and in the solid state.

The temperature dependence of the spectral width of singlet oxygen dimole emission

In the temperature range of T = 150–400 K, the dependence of spectral widths (cm−1) on temperature, 182 + 0.38(±0.01)T and 217 + 0.48(±0.01)T, respectively, has been obtained for dimole emission of O2(a, 0) + O2(a, 0) → O2(X, 1) + O2(X, 0) + hν (λ = 703 nm) and O2(a, 0) + O2(a, 0) → O2(X, 0) + O2(X, 0) + hν (λ = 634 nm). It was shown that the ratio of dimole emission rate constants does not depend on temperature in the range of 150–400 K and is 1.06 ± 0.01.