Showing papers on "Flash photolysis published in 2011"
TL;DR: It is proposed that the photo enhancement should be a general phenomenon in gold catalysis for those reaction mechanisms involving positive and/or negative gold species.
Abstract: Laser flash photolysis of supported gold nanopar-ticles exciting at the surface plasmon band (532 nm) has allowed in the case of Au/CeO2 and Au/OH-npD (OH-npD: Fenton-treated diamond nanoparticles) detection of transients decaying in the microsecond time scale that have been attributed as indicating photoinduced electron ejection from gold based on N2O quenching and the observation of the generation of methyl viologen radical cations. This photochemical behavior has led us to hypothesize that there could be assistance to the catalytic activity of these materials by irradiation in those cases wherein the mechanism involves electron transfer to or from a substrate to the gold. This hypothesis has been confirmed by observing that the catalytic activity of Au/OH-npD for the Fenton degradation of phenol with hydrogen peroxide can be increased over 1 order of magnitude by irradiation at 532 nm. Moreover, there is a linear relationship between the initial reaction rate and the incident photon flux. This photoenh...
228 citations
TL;DR: In this paper, a new concept based on the photoredox catalysis is proposed for the design of a photoinitiating system able to efficiently generate, in a single catalytic cycle, both a radical and a cation as initiating species.
167 citations
TL;DR: In this paper, the photocatalytic bromination of aromatic hydrocarbons by molecular oxygen with hydrogen bromide occurs efficiently to produce monobrominated products selectively using 9-mesityl-10-methylacridinium ion (Acr+−Mes) as a photocatalyst under visible light irradiation.
Abstract: Photocatalytic bromination of aromatic hydrocarbons by molecular oxygen with hydrogen bromide occurs efficiently to produce monobrominated products selectively using 9-mesityl-10-methylacridinium ion (Acr+–Mes) as a photocatalyst under visible light irradiation. Both the product yield and selectivity for the bromination of 1,3,5-trimethoxybenzene were 100% with a quantum yield of 4.8%. The photocatalytic turnover number is 900 based on the initial concentration of Acr+–Mes. The reactive radical intermediates involved in the photocatalytic cycle have been successfully detected by laser flash photolysis measurements. The photocatalytic bromination is initiated by photoinduced electron transfer from the mesitylene moiety to the singlet excited state of acridinium ion, which results in formation of the electron-transfer state of Acr+–Mes (Acr˙–Mes˙+), followed by electron transfer from aromatic hydrocarbons to the mesitylene radical cation moiety and electron transfer from the acridinyl radical moiety to O2. The resulting radical cations of aromatic hydrocarbons react with Br− to produce the corresponding monobrominated products selectively.
155 citations
TL;DR: Sorbic acid (trans,trans-hexadienoic acid) was developed as a probe for the quantification of the formation rate, overall solution scavenging rate and steady-state concentrations of triplet-excited states of organic compounds.
148 citations
TL;DR: The photostability and fluorescence properties of 1,3-diphenylisobenzofuran (DPBF), a popular singlet oxygen (1O2 or 1Δg) trapping agent used in various solvents, are examined by UV-vis absorption, steady-state and time-resolved fluorescence techniques, as well as laser flash photolysis.
107 citations
TL;DR: In this article, photoinduced electron transfer (PET) within the nano assembly is revealed by laser flash photolysis, time resolved and steady state fluorescence, as well as UV-vis absorption techniques.
85 citations
TL;DR: The appearance of pH-dependent decreases in the efficiency of formation of TiO(2)-Ru(3+) and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH- dependent back electron transfer processes on both the sub-nanosecond and millisecond-microsecond time scales could be significant in limiting long-term storage of multiple redox equivalents.
Abstract: Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru(bpy)2(4,4'-(PO3H2)2bpy)]2+ surface-bound to TiO2 (TiO2-RuII). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, , were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO2(e-)-Ru3+→TiO2-Ru2+. The appearance of pH-dependent decreases in the efficiency of formation of TiO2-Ru3+ and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond–microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.
71 citations
TL;DR: The primary processes in the photochemistry of Fe(III) complexes with carboxylic acids (glyoxalic, tartaric, pyruvic and lactic) were studied by means of laser flash photolysis and the main channel was proposed to be the formation of a long-lived radical complex.
Abstract: The primary processes in the photochemistry of Fe(III) complexes with carboxylic acids (glyoxalic, tartaric, pyruvic and lactic) were studied by means of laser flash photolysis. The inner-sphere electron transfer with the formation of Fe(II) complex and an escape of an organic radical to the solution bulk was shown to be a minor channel of the photolysis. The main channel was proposed to be the formation of a long-lived radical complex [FeII⋯˙OOC-R]2+. Spectral and kinetic parameters of the radical complexes are determined.
67 citations
TL;DR: In this article, eight N-heterocyclic carbene-borane (NHC-boranes) are proposed as new efficient co-initiators for acrylate photopolymerization reactions.
62 citations
TL;DR: In this paper, the authors investigated the use of [(Ru(bpy)2(4,4′-(PO3H2)2bpy)]2+ attached to TiO2 nanoparticle films, which were used in a dye-sensitized photoelectrosynthesis cell for H2 production.
Abstract: Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [(Ru(bpy)2(4,4′-(PO3H2)2bpy)]2+ attached to TiO2 nanoparticle films, TiO2−RuII, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H2 production. In these experiments, laser flash excitation of TiO2−RuII and rapid injection lead to TiO2(e−)−RuIII with subsequent TiO2(e−)−RuIII → TiO2−RuII back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA4−) as irreversible electron transfer donors. With added TEOA or EDTA4−, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H2 production in the photoelectrosynthesis cell. Reduction of TiO2(e−)−RuIII by both TEOA and EDTA4− occurs with kD ∼ 106 M−1 s−1. EDTA4− is a more efficient scavenger by a factor of ∼3 because of a more favorable partition equilibrium between the film and the externa...
57 citations
TL;DR: Evidence suggests that reaction at the OH site is significant at the authors' higher temperatures: 47-53% at 865 K, and estimates were made for k(1.1) and the fractional production of CH(2)CH(2).
Abstract: The rate coefficients for reactions of OH with ethanol and partially deuterated ethanols have been measured by laser flash photolysis/laser-induced fluorescence over the temperature range 298−523 K and 5−100 Torr of helium bath gas. The rate coefficient, k1.1, for reaction of OH with C2H5OH is given by the expression k1.1 = 1.06 × 10−22T3.58 exp(1126/T) cm3 molecule−1 s−1, and the values are in good agreement with previous literature. Site-specific rate coefficients were determined from the measured kinetic isotope effects. Over the temperature region 298−523 K abstraction from the hydroxyl site is a minor channel. The reaction is dominated by abstraction of the α hydrogens (92 ± 8)% at 298 K decreasing to (76 ± 9)% with the balance being abstraction at the β position where the errors are 2σ. At higher temperatures decomposition of the CH2CH2OH product from β abstraction complicates the kinetics. From 575 to 650 K, biexponential decays were observed, allowing estimates to be made for k1.1 and the fraction...
TL;DR: The photophysics of N,N'-bis(salicylidene)-p-phenylenediamine (BSP) is analyzed both theoretically and experimentally and shows a very fast (less than 100 fs) photoinduced single proton transfer process leading to a phototautomer where asingle proton has moved.
Abstract: The photophysics of N,N'-bis(salicylidene)-p-phenylenediamine (BSP) is analyzed both theoretically and experimentally. The alternative intramolecular proton-transfer reactions lead to three different tautomers. We performed DFT and TDDFT calculations to analyze the topography of the reactions connecting the three tautomers. Deactivation paths through a Conical Intersection (CI) region are also analyzed to explain the low fluorescence quantum yield of the phototautomers. The complex molecular structure of BSP provides a large number of deactivation paths, almost all of them energetically available following the initial photoexcitation. Femtosecond (fs) time-resolved emission studies in solution and flash photolysis experiments (nano to millisecond regime) were performed to get detailed information on the time domain of the full photocycle. The picture that emerges by combining theoretical and experimental results shows a very fast (less than 100 fs) photoinduced single proton transfer process leading to a phototautomer where a single proton has moved. This species may deactivate through a low-energy CI leading in about 20 ps to a rotameric form in the ground state that has a lifetime of several tens of microseconds in solution. This process competes with another deactivation path taking place prior to the proton-transfer reaction which involves a low-energy CI leading to a rotamer of the enol structure. In the flash photolysis studies, the rotamer of the enol structure was directly identified by the positive transient absorption band in the 250-260 nm and its lifetime in n-hexane (10 ms) is almost 3 orders of magnitude longer than the lifetime of the photochrome (around 40 μs). Our findings do not exclude a double proton transfer reaction in the excited enol form to give a tautomer in less than 100 fs during the first (impulsive) phase of the reaction which reverts back to the photoproducts of the simple proton transfer in 1-3 ps.
TL;DR: In this article, a one-component visible photoinitiator based on 9-(2-Morpholine-4yl-acetyl)-5-thia-napthasen-12-one (TX-MPM) was used as an initiator for the polymerization of methyl methacrylate (MMA).
Abstract: Thioxanthone-based 9-(2-Morpholine-4yl-acetyl)-5- thia-napthasen-12-one (TX-MPM) was synthesized and charac- terized as a one-component novel visible photoinitiator. Its capability to act as an initiator for the polymerization of methyl methacrylate (MMA) was examined in photoreactor and also daylight. Photophysical properties: fluorescence and phospho- rescence emission spectra and fluorescence quantum yield of TX-MPM (Uf ¼ 0.29) were determined. The phosphorescence lifetime was found 131 ms for TX-MPM and 110 ms for initia- tor-attached polymer (PMMA) at 77 K, indicated a p!p* nature of the lowest triplet state. A model compound, morpholino acetonapthone was used as quencher for the triplet states of TX- MPM and the quenching rate constant was determined (kq ¼ 1.26 � 10 9 M � 1 s � 1 ). According to laser flash photolysis studies, intermolecular hydrogen abstraction process was more domi- nant path to the formation of the initiating radicals. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4037-4043, 2011
TL;DR: The obtained results demonstrate that the quality of the secondary UV filters is inferior compared to the primary ones, which may result in a higher susceptibility of old lenses to UV light, and might be an important factor for the development of the age-related cataract.
Abstract: PURPOSE. To compare the photochemical properties of UV filter molecules present in the human lens (kynurenine, KN; 3-hy- droxykynurenine, 3OHKN; 3-hydroxykynurenine O-gluco- side, 3OHKG; 4-(2-aminophenyl)-4-oxobutanoic acid, AHA; and glutathionyl-kynurenine, GSH-KN) with the use of the following parameters: excited singlet lifetime, fluorescence quantum yield, triplet quantum yield, photodecomposition quantum yield. METHODS. The excited singlet lifetimes were measured with the use of fluorescence upconversion (time resolution, 210 fs) and pump-probe transient absorption (time resolution, 200 fs) methods. The fluorescence quantum yields were determined relative to an aqueous solution of quinine bisulfate. The triplet quantum yields were measured with the use of nanosecond laser flash photolysis. The photodecomposition quantum yields were determined by steady state photolysis followed by the high-performance liquid chromatography analysis. RESULTS. The secondary UV filters—AHA and GSH-KN are better photosensitizers than the primary ones -KN, 3OHKN and 3OHKG: the singlet state lifetimes of the secondary UV filters are longer, and the quantum yields of fluorescence and triplet state formation are higher. CONCLUSIONS. With aging, the ratio primary/secondary UV filters in the human lens decreases from approximately 10:1 to 2:1. The obtained results demonstrate that the quality of the secondary UV filters is inferior compared to the primary ones, which may result in a higher susceptibility of old lenses to UV light. That might be an important factor for the development of the age-related cataract.
TL;DR: Owing to the NIs redox and recognition properties, these results represent the first step toward new molecular devices capable of both biological target recognition and photoreleasing of QMs as alkylating species, under physiological conditions.
Abstract: Photochemical activation of water-soluble 1,8-naphthalimide derivatives (NIs) as alkylating agents has been achieved by irradiation at 310 and 355 nm in aqueous acetonitrile. Reactivity in aqueous and neat acetonitrile has been extensively investigated by laser flash photolysis (LFP) at 355 nm, as well as by steady-state preparative irradiation at 310 nm in the presence of water, amines, thiols, and ethyl vinyl ether. Product distribution analysis revealed fairly efficient benzylation of the amines, hydration reaction, and 2-ethoxychromane generation, in the presence of ethyl vinyl ether, resulting from a [4 + 2] cycloaddition onto a transient quinone methide. Remarkably, we found that the reactivity was dramatically suppressed under the presence of oxygen and radical scavengers, such as thiols, which was usually associated with side product formation. In order to unravel the mechanism responsible for the photoreactivity of these NI-based molecules, a detailed LFP study has been carried out with the aim t...
TL;DR: In this paper, the photopolymerization process of acrylate coat-ings initiated by visible light (k > 380 nm) and performed in air was studied in the presence of zirconium complexes.
Abstract: The photopolymerization process of acrylate coat- ings initiated by visible light (k > 380 nm) and performed in air was studied in the presence of zirconium complexes. Depth profiling experiments were performed using confocal Raman microscopy showing that the conversion, which is low at the surface of the sample, increases with increasing depth and reaches a full conversion close to the substrate. RT-FTIR spectroscopy corroborates Raman results in evidencing the efficiency of some zirconium compounds to reduce oxygen in- hibition. Finally, laser flash photolysis experiments revealed that the beneficial effect in air is attributable to the reaction of the zirconium complex on the peroxyl radicals formed from the reaction of oxygen with radicals. Therefore, the oxygen present in the medium is depleted, allowing a better effi- ciency of the photopolymerization process. V C 2011 Wiley Peri- odicals, Inc. J Polym Sci Part A: Polym Chem 49: 5169-5175, 2011
TL;DR: The calculations show that the triplet exciton of chromophores with electron-withdrawing substituents is localized away from the central platinum atom, red-shifting the spectra and increasing the tripleT-state lifetime.
Abstract: To explore spectroscopic structure−property relationships in platinum acetylides, we synthesized a series of complexes having the molecular formula trans-bis(tributylphosphine)-bis(4-((9,9-diethyl-7-ethynyl-9H-fluoren-2-yl)ethynyl)-R)-platinum. The substituent, R = NH2, OCH3, N(phenyl)2, t-butyl, CH3, H, F, benzothiazole, CF3, CN, and NO2, was chosen for a systematic variation in electron-donating and -withdrawing properties as described by the Hammett parameter σp. UV/vis, fluorescence, and phosphorescence spectra, transient absorption spectra on the fs−ps time scale, and longer time scale flash photolysis on the ns time scale were collected. DFT and TDDFT calculations of the T1 and S1 energies were performed. The ES and ET values measured from linear spectra correlate well with the calculated results, giving evidence for the delocalized MLCT character of the S1 state and confinement of the T1 exciton on one ligand. The calculated T1 state dipole moment ranges from 0.5 to 14 D, showing the polar, charge-...
TL;DR: The rate constants of their reactions with nucleophiles provide the first direct comparison of the electrophilicities of iminium ions derived from MacMillan's first- and second-generation catalysts.
Abstract: Two at a time: α,β-Unsaturated iminium ions can be generated by laser flash photolysis of enaminophosphonium ions. The rate constants of their reactions with nucleophiles provide the first direct comparison of the electrophilicities of iminium ions derived from MacMillan's first- and second-generation catalysts.
TL;DR: The high potential of this reaction is evidenced here when using a decatungstate/silane/diphenyl iodonium salt combination as an initiating system for the ring opening photopolymerization of epoxides.
Abstract: The use of decatungstate (W10O32(4-)) in combination with silanes to generate silyl radicals under green fluorescence bulb irradiation as well as sunlight exposure is described. The mechanisms are investigated by ESR and laser flash photolysis experiments. The high potential of this reaction is evidenced here when using a decatungstate/silane/diphenyl iodonium salt combination as an initiating system for the ring opening photopolymerization of epoxides.
TL;DR: The calculations show that 3 has significant 1,3-carbon iminyl biradical character, which explains why 3 reacts efficiently with oxygen and decays by intersystem crossing to the singlet surface.
Abstract: The photoreactivity of (3-methyl-2H-azirin-2-yl)-phenylmethanone, 1, is wavelength-dependent (Singh et al. J. Am. Chem. Soc. 1972, 94, 1199−1206). Irradiation at short wavelengths yields 2P, whereas longer wavelengths produce 3P. Laser flash photolysis of 1 in acetonitrile using a 355 nm laser forms its triplet ketone (T1K, broad absorption with λmax ∼ 390–410 nm, τ ∼ 90 ns), which cleaves and yields triplet vinylnitrene 3 (broad absorption with λmax ∼ 380–400 nm, τ = 2 μs). Calculations (B3LYP/6-31+G(d)) reveal that T1K of 1 is located 67 kcal/mol above its ground state (S0) and has a long C–N bond (1.58 A), and the calculated transition state to form 3 is only 1 kcal/mol higher in energy than T1K of 1. The calculations show that 3 has significant 1,3-carbon iminyl biradical character, which explains why 3 reacts efficiently with oxygen and decays by intersystem crossing to the singlet surface. Photolysis of 1 in argon matrixes at 14 K produced ketene imine 7, which presumably is formed from 3 intersyste...
TL;DR: The photophysical behavior of acridine shows a facilitated water assisted protonation equilibrium between its deprotonated and protonated forms within a confined environment of sodium dodecyl sulphate micelles above the critical micellar concentration of 8 mM.
Abstract: The photophysical behavior of acridine (Acr) shows a facilitated water assisted protonation equilibrium between its deprotonated (Acr* ∼ 3.4 ns) and protonated forms (AcrH+* ∼ 33 ns) within a confined environment of sodium dodecyl sulphate (SDS) micelles above the critical micellar concentration of 8 mM. The acidic interface of the micelles is capable of protonating Acr whereas deprotonated Acr is partitioned into the hydrophobic core. The time-resolved-area-normalized-emission spectra confirm the presence of both Acr* and AcrH+*, while time-resolved-emission spectra depict time evolution between them. Quenching of AcrH+* with triethylamine (TEA) results in a linear Stern–Volmer (S–V) plot, whereas non-linearity arises with N,N-dimethylaniline (DMA). Both steady-state and time-resolved quenching results with TEA are explained on the basis of excited state proton transfer (ESPT), however the reasons behind the quenching of excited Acr with DMA are proposed as ESPT followed by a photoinduced electron transfer. Partitioning of DMA at the interface makes it accessible for both Acr* and AcrH+* in hydrophobic and hydrophilic regions of micelles respectively. The rate of electron transfer at the interface is found to be slower compared to that in the hydrophobic core. Characterization of transient intermediates formed during ESPT and PET between Acr and amines by laser-flash photolysis also supports the observation obtained during fluorescence studies. The mode of interactions between Acr and amines inside micelles is controlled by the localization of the proton/electron donors and acceptors in different hydrophobic or hydrophilic regions of such nano-confined environments.
TL;DR: In this paper, the photocyclization reaction of 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT) in methanol was studied by using nanosecond laser flash photolysis at 296 K.
Abstract: Photocyclization reaction of 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT) in methanol was studied by using nanosecond laser flash photolysis at 296 K. When xanthone was used as a trip...
TL;DR: BBT's high solubility in common solvents combined with its measured enhanced optoelectronic properties make it a candidate as a universal fluorophore reference and smart material for both polymeric and solution studies.
Abstract: The photophysics of 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT) were investigated for assessing its limitations for use as a universal fluorophore and as a viable sensor for both polymeric and solution studies. This is of importance given the limitations of currently used materials. BBT’s steady-state and time-resolved fluorescence were additionally investigated to correlate its solid-state features, observed by fluorescence spectroscopy when mixed in poly(1,4-butylene succinate) (PBS) films, with its single crystal characteristics. The conjugated fluorophore was found to be highly fluorescent, with absolute quantum yields of (Φfl) ≥ 0.60. The Φfl values were high, regardless of solvent polarity and proticity and whether alone or in polymeric films. The major competitive fluorescence quenching pathway was found to occur by intersystem crossing to the triplet state. This was confirmed by laser flash photolysis in which the BBT triplet absorbed at 500 nm. The triplet transient was confirmed by quen...
TL;DR: In aqueous media, photochemical excitation of hydroxyadamantyl, diphenylhydroxymethyl, and hydroxypropyl derivatives of 4-phenylphenol 5-9 leads to solvent-assisted deprotonation of the phenol OH, and protonations of the benzyl alcohol coupled with dehydration, that delivers quinone methides (QMs) 14-18.
Abstract: In aqueous media, photochemical excitation (S1) of hydroxyadamantyl, diphenylhydroxymethyl, and hydroxypropyl derivatives of 4-phenylphenol 5–9 leads to solvent-assisted deprotonation of the phenol OH, and protonation of the benzyl alcohol coupled with dehydration, that delivers quinone methides (QMs) 14–18. The QMs react with CH3OH converting them in high quantum yields to the photosolvolysis products (overall Φ ∼ 0.1–0.5). QMs were characterized by laser flash photolysis in CH3CN–H2O and TFE. In TFE, the zwitterionic QM 15 has a lifetime of 250 ns, whereas para QMs 16 and 17 have lifetimes of 500 μs and 1.1 s, respectively. Introduction of the steric hindrance to the parent QM structure (with the adamantyl moiety), or additional stabilization by two phenyl rings, results in an increase of QM lifetimes and selectivity in the reactions with nucleophiles. In vitro studies of the antiproliferative activity of photochemically generated QMs 15–17 were carried out on one human cancer cell line. Irradiation of cells incubated with 7 showed enhanced antiproliferative activity compared to cells that were not irradiated, in accordance with the activity being due to the formation of QM 16.
TL;DR: The feasibility of an electron transfer imino-Diels-Alder reaction between N-benzylideneaniline and arylalkenes in the presence of a pyrylium salt as a photosensitizer has been demonstrated by a combination of product studies, laser flash photolysis (LFP), and DFT theoretical calculations.
TL;DR: The triplet quantum yield of SiPc unit in the supra-molecule is unexpectedly high, and the predominant spectral signal in microsecond-scale is triplet-triplet (T(1)-T(n)) absorption.
Abstract: Silicon phthalocyanine (SiPc) with two axially attached morpholine (MP) units was prepared, and its photophysics was studied by laser flash photolysis, steady state and time-resolved fluorescence m...
TL;DR: The kinetics of the OH reaction in an industrial sample of octofluoro-2-propene (a mixture of the cis- and trans-isomers of CF(3)CF═CFCF(3)) was studied and the "effective" reaction rate constant for the typically industrial mixture was studied.
Abstract: The rate constants for the reactions of OH radicals with fully fluorinated alkenes containing different numbers of −CF3 groups next to olefinic carbon, CF2═CF2, CF2═CFCF3, CF3CF═CFCF3, and (CF3)2C═CFC2F5, were measured between 230 and 480 K using the flash photolysis resonance fluorescence technique to give the following expressions: kC2F4(250−480 K) = 1.32 × 10−12 × (T/298 K)0.9 × exp(+600 K/T) cm3 molecule−1 s−1, kC3F6(230−480 K) = 9.75 ×10−14 × (T/298 K)1.94 × exp(+922 K/T) cm3 molecule−1 s−1, ktrans-C4F8(230−370 K) = 7.50 × 10−14 × (T/298 K)1.68 × exp(+612 K/T) cm3 molecule−1 s−1, kcis-C4F8(230−370 K) = 2.99 × 10−14 × (T/298 K)2.61 × exp(+760 K/T) cm3 molecule−1 s−1, and kC6F12(250−480 K) = 2.17 × 10−15 × (T/298 K)3.90 × exp(+1044 K/T) cm3 molecule−1 s−1. The kinetics of the OH reaction in an industrial sample of octofluoro-2-propene (a mixture of the cis- and trans-isomers of CF3CF═CFCF3) was studied to determine the “effective” reaction rate constant for the typically industrial mixture: k⟨C4F8⟩(230...
TL;DR: In this paper, the triplet state of the cationic dye phenosafranine covalently attached to the polymer chain was investigated using laser flash excitation, which revealed the existence of an intermediate structure akin to a micellar segment in PMAA prior to the formation of elongated linear chain.
TL;DR: In this paper, a laser flash photolysis with magnetic field (MF ∼0.08 T) has been used to study interaction between Acridine (Acr) and Triethylamine (TEA) in reverse micelles with w 0 ǫ = 2.5 −40.
TL;DR: Detailed kinetic and mechanistic studies were performed on the reversible binding of NO to FeCl(2) dissolved in the IL 1-ethyl-3-methylimidazolium dicyanamide as a solvent, and it was concluded that its electronic structure is best described by the presence of a high-spin Fe(III) center antiferromagnetically coupled to NO(-) (S = 1), yielding the observed spin quartet ground state.
Abstract: To elucidate the applicability and properties of ionic liquids (ILs) to serve as chemical reaction media for the activation of small molecules by transition-metal complexes, detailed kinetic and mechanistic studies were performed on the reversible binding of NO to FeCl2 dissolved in the IL 1-ethyl-3-methylimidazolium dicyanamide ([emim][dca]) as a solvent. We report, for the first time, the application of laser flash photolysis at ambient and high pressure to study the kinetics of this reaction in an IL. The kinetic data and activation parameters for the “on” and “off” reactions suggest that both processes follow a limiting dissociative (D) ligand substitution mechanism, in contrast to that reported for the same reaction in aqueous solution, where this well-known “brown-ring” reaction follows an interchange dissociative (Id) ligand substitution mechanism. The observed difference apparently arises from the participation of the IL anion as a N-donor ligand, as evidenced by the formation of polymeric [Fe(dca...