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Yancheng Liu - One of the best experts on this subject based on the ideXlab platform.
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laser Flash Photolysis mechanism of anthraquinone 2 sodium sulfonate in pyridine ionic liquid water mixed system
Chinese Journal of Chemical Physics, 2016Co-Authors: Guanglai Zhu, Yancheng Liu, Liangwei Zhang, Zhifeng CuiAbstract:The photochemical reaction process of anthraquinone-2-sodium sulfonate (AQS) in the mixture of water (H2O) and N-butylpyridinium tetrafluoroborate ([BPy][BF4]) was studied using the laser Flash Photolysis technique. Experimental results show that the excited triplet of AQS (3AQS*) could react rapidly with H2O and the transient absorption spectra greatly changed by increasing the volume fraction of the ionic liquid (VIL) in [BPy][BF4]/H2O mixtures. The absorbance at 510 nm increased gradually with increasing VIL when 0 0.1. Otherwise, the absorbance of the band near 380 nm steadily increased. The apparent kinetic parameters of transient species B and 3AQS* are obtained approximately. 3AQS* abstracting hydrogen from [BPy]+ was also explored. It was deduced that the 350–420 nm band was the superposition of the peaks of 3AQS* and AQSH·. The two reactions of 3AQS* with [BPy][BF4] and H2O are a pair of competitive reactions. We also conclud...
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laser Flash Photolysis mechanism of anthraquinone 2 sodium sulfonate in pyridine ionic liquid water mixed system
Chinese Journal of Chemical Physics, 2016Co-Authors: Guanglai Zhu, Yancheng Liu, Liangwei Zhang, Zhifeng CuiAbstract:The photochemical reaction process of anthraquinone-2-sodium sulfonate (AQS) in the mixture of water (H2O) and N-butylpyridinium tetrafluoroborate ([BPy][BF4]) was studied using the laser Flash Photolysis technique. Experimental results show that the excited triplet of AQS (3AQS*) could react rapidly with H2O and the transient absorption spectra greatly changed by increasing the volume fraction of the ionic liquid (VIL) in [BPy][BF4]/H2O mixtures. The absorbance at 510 nm increased gradually with increasing VIL when 0 0.1. Otherwise, the absorbance of the band near 380 nm steadily increased. The apparent kinetic parameters of transient species B and 3AQS* are obtained approximately. 3AQS* abstracting hydrogen from [BPy]+ was also explored. It was deduced that the 350–420 nm band was the superposition of the peaks of 3AQS* and AQSH·. The two reactions of 3AQS* with [BPy][BF4] and H2O are a pair of competitive reactions. We also concluded that the entire reaction processes slow down in the case of high [BPy][BF4] concentrations.
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photochemical properties of gemifloxacin a laser Flash Photolysis study
Journal of Photochemistry and Photobiology B-biology, 2015Co-Authors: Yancheng Liu, Peng Zhang, Jianfeng Zhao, Wenfeng WangAbstract:The photochemical properties of gemifloxacin (GEFX), a fluoroquinolone antibacterial drug that exhibits phototoxicity toward biological substrates, were studied in aqueous solutions by laser Flash Photolysis (LFP) and pulse radiolysis. GEFX triplet state ((3)GEFX*) absorption spectra showed maximum absorption at 510 nm. (3)GEFX* was quenched by naproxen (NAP) via energy transfer with a rate constant of 1.2 x 10(8) dm(3) mol(-1) s(-1). The energy of (3)GEFX* was 266 kJ mol(-1) and the transient absorption spectra showed direct evidence of electron transfer from 2'-deoxyguanosine-5'-monophosphate, N,N,N',N'-tetramethyl-p-phenylenediamine, and tryptophan to (3)GEFX* with bimolecular reaction rate constants of 4.1 x 10(6), 2.0 x 10(7), and 2.2 x 10(7) dm(3) mo1(-1) s(-1), respectively. The rate constants for reactions of GEFX with 'OH, ea, were found to be 1.5 x 10(10) and 1.4 x 10(10) dm(3) mol(-1) s(-1), respectively. The mechanisms and products of the photosensitive damage of lysozyme were related to the GEFX concentration, irradiation time, and ambient conditions. (C) 2014 Elsevier B.V. All rights reserved.
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photosensitized oxidation of tryptophan and tyrosine by aromatic ketones a laser Flash Photolysis study
Science China-chemistry, 2012Co-Authors: Ruizhi Tang, Peng Zhang, Yancheng Liu, Wenfeng WangAbstract:Photochemical processes of benzophenone (BP) and xanthone (XT) with tryptophan (TrpH) and tyrosine (TyrOH) were studied using the laser Flash Photolysis technique. It has been observed that the triplet state of BP and XT reacted with TrpH and TyrOH by hydrogen transfer with the formation of BP and XT ketyl radicals and oxidized radicals of Trp· and TyrO·. The related rate constants of these reactions were determined in this paper. The free energy changes (ΔG) of these reactions suggested that the proposed hydrogen transfer mechanism was thermodynamically feasible. These results provide theoretical foundation for further studying structural effects on the photochemical behaviors of proteins with triplet state BP and XT.
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photophysical properties of gatifloxacin in aqueous solution by laser Flash Photolysis and pulse radiolysis
Radiation Physics and Chemistry, 2012Co-Authors: Peng Zhang, Side Yao, Ruizhi Tang, Yancheng Liu, Zhaoguo Xing, Wenfeng WangAbstract:Abstract GFX in water, at pH 7.0, shows intense absorption bands with peaks at 284 and 333 nm, ( e =24,670 and 12,670 M −1 cm −1 ). Both the absorption and emission properties of GFX were pH-dependent; the p K a values for the protonation equilibria of the ground state (5.7 and 8.9) and excited singlet state (3.6 and 7.5) of GFX were determined spectroscopically. GFX fluoresces weakly, with a maximum quantum yield for fluorescence emission (0.06) at pH 4.7. A series of experiments were performed to characterize the transient species of GFX in aqueous solution using laser Flash Photolysis and pulse radiolysis. GFX undergoes monophotonic photoionization with a quantum yield of 0.16 on a 355 nm laser excitation. This process leads to the formation of a long-lived cation radical with a maximum absorption at 380 nm. Triplet–triplet absorption had maximum absorption at 510 nm. The reaction of GFX with one-electron oxidant N 3 • was investigated and the bimolecular rate constant was determined to be 3.1×10 9 M −1 s −1 .
Hermenegildo García - One of the best experts on this subject based on the ideXlab platform.
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laser Flash Photolysis of dioxo iron phthalocyanine intercalated in hydrotalcite and its use as a photocatalyst
Journal of Photochemistry and Photobiology A-chemistry, 2009Co-Authors: Luca Maretti, Juan C. Scaiano, Mercedes Alvaro, Esther Carbonell, Hermenegildo GarcíaAbstract:Abstract Dioxo iron phthalocyanine tetrasulphonate (FeO2Pc) has been incorporated inside the intergallery space of a layered double oxide (LDH). Evidence for the inclusion of the FeO2Pc inside the intergallery spaces of LDH was obtained from the expansion of the basal layer distance of the host. The resulting material (0.10–0.13 mmol FeO2Pc × g−1) exhibits the optical spectrum characteristic of isolated metal phthalocyanine. Laser Flash Photolysis of the solid allows detecting the triplet excited state of the metal complex as a long-lived transient species whose decay is not complete in 2 ms. The solid is able to act as an effective photocatalyst for the degradation of aqueous phenol.
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laser Flash Photolysis of metal oxide supported vanadyl catalysts spectroscopic evidence for the ligand to metal charge transfer state
Journal of Materials Chemistry, 2006Co-Authors: Hermenegildo García, Emilio Palomares, Jose Manuel Lopeznieto, Heinz D Roth, Benjamin SolsonaAbstract:A series of vanadyl containing samples supported on metal oxides (SiO2, Al2O3, K-doped Al2O3, TiO2, MgO and ZnO) have been studied by laser Flash Photolysis. Excitation at 266 or 308 nm generated transients (300 nm < λmax < 500 nm) with lifetimes on the microsecond time scale. These were assigned to the ligand-to-metal charge-transfer triplet excited state. The absorption maximum varied with the nature of the support. Samples having higher vanadium loading showed additional transients attributed to vanadyl aggregates.
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an organically modified single wall carbon nanotube containing a pyrene chromophore fluorescence and diffuse reflectance laser Flash Photolysis study
Chemical Physics Letters, 2004Co-Authors: Mercedes Alvaro, Pedro Atienzar, Jose L Bourdelande, Hermenegildo GarcíaAbstract:Abstract SWNT was functionalized with N -(1-pyrenylmethyl)-1,5-diaminopentane and the resulting PY ∝ SWNT sample characterized by optical and IR spectroscopy. The photochemical properties of PY ∝ SWNT were studied by dispersing the insoluble solid in silica and applying diffuse reflectance techniques. From the emission decay kinetics (quenching of pyrenyl singlet excited state by the SWNT walls) and laser Flash Photolysis (detection of pyrenyl radical cation) evidence in support of occurrence of an intramolecular quenching from pyrenyl singlet excited state to the SWNT walls has been obtained.
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Laser Flash Photolysis Study of Jacobsen Catalyst and Related Manganese(III) Salen Complexes. Relevance to Catalysis
Journal of the American Chemical Society, 2001Co-Authors: María J. Sabater, Mercedes Alvaro, Hermenegildo García, Emilio Palomares, Juan C. ScaianoAbstract:The laser Flash Photolysis and emission properties of a set of five-coordinate manganese(III) Schiff-base complexes have been examined. In contrast to the intramolecular electron transfer between Mn3+ and the equatorial salen ligand reported to occur in the absence of axial coordination, our laser Flash Photolysis study has shown that the reactivity of the respective excited states is appreciably influenced by the electron donor strength of the apical ligand at the metal center. In fact, homolytic and heterolytic photocleavage of the metal-ligand apical bond can be the most important processes upon laser excitation, their relative contribution being influenced by medium effects and the sigma-charge donation of the axial ligand. On the other hand, the detection of reactive intermediates such as the oxomanganese(V) salen complex (lambda(max) 530 nm) by laser Flash Photolysis opens the way to apply this fast detection technique to the study of reaction mechanisms in catalysis by metallic complexes. As a matter of fact, quenching of oxomanganese(V) salen by simple alkenes has been observed by laser Flash.
Francisco Bosca - One of the best experts on this subject based on the ideXlab platform.
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seeking the mechanism responsible for fluoroquinolone photomutagenicity a pulse radiolysis steady state and laser Flash Photolysis study
Free Radical Biology and Medicine, 2014Co-Authors: Sonia Soldevila, Consuelo M Cuquerella, Virginie Lhiaubetvallet, Ruth Edge, Francisco BoscaAbstract:Abstract The mechanism responsible for the remarkable photomutagenicity of fluoroquinolone (FQ) antibiotics remains unknown. For this reason, it was considered worthwhile to study in detail the interactions between DNA and a dihalogenated FQ such as lomefloxacin (LFX; one of the most photomutagenic FQs) and its N -acetyl derivative ALFX. Studies of photosensitized DNA damage by (A)LFX, such as formation of DNA single-strand breaks (SSBs), together with pulse radiolysis, laser Flash Photolysis, and absorption and fluorescence measurements, have shown the important effects of the cationic character of the piperazinyl ring on the affinity of this type of drug for DNA. Hence, the formation of SSBs was detected for LFX, whereas ALFX and ciprofloxacin (a monofluorated FQ) needed a considerably larger dose of light to produce some damage. In this context, it was determined that the association constant ( K a ) for the binding of LFX to DNA is ca. 2×10 3 M −1 , whereas in the case of ALFX it is only ca. 0.5×10 3 M −1 . This important difference is attributed to an association between the cationic peripheral ring of LFX and the phosphate moieties of DNA and justifies the DNA SSB results. The analysis of the transient species detected and the photomixtures has allowed us to establish the intermolecular processes involved in the Photolysis of FQ in the presence of DNA and 2'-deoxyguanosine (dGuo). Interestingly, although a covalent binding of the dihalogenated FQ to dGuo occurs, the photodegradation of FQ…DNA complexes did not reveal any significant covalent attachment. Another remarkable outcome of this study was that (A)LFX radical anions, intermediates required for the onset of DNA damage, were detected by pulse radiolysis but not by laser Flash Photolysis.
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a laser Flash Photolysis and pulse radiolysis study of primary photochemical processes of flumequine
Photochemistry and Photobiology, 2000Co-Authors: Maela Bazin, M L Marin, Francisco Bosca, Miguel A Miranda, L. K. Patterson, René SantusAbstract:Abstract The 355 nm laser Flash Photolysis of argon-saturated pH 8 phosphate buffer solutions of the fluoroquinolone antibiotic flumequine produces a transient triplet state with a maximum absorbance at 575 nm where the molar absorptivity is 14 000 M−1 cm−1. The quantum yield of triplet formation is 0.9. The transient triplet state is quenched by various Type-1 photodynamic substrates such as tryptophan (TrpH), tyrosine, N-acetylcysteine and 2-deoxyguanosine leading to the formation of the semireduced flumequine species. This semireduced form has been readily identified by pulse radiolysis of argon-saturated pH 8 buffered aqueous solutions by reaction of the hydrated electrons and the CO2·− radicals with flumequine. The absorption maximum of the transient semireduced species is found at 570 nm with a molar absorptivity of 2500 M−1 cm−1. In argon-saturated buffered solutions, the semireduced flumequine species formed by the reaction of the flumequine triplet with TrpH stoichiometrically reduces ferricytoch...
Matthew S. Platz - One of the best experts on this subject based on the ideXlab platform.
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Photochemistry of Tetrasulfur Tetranitride: Laser Flash Photolysis and Quantum Chemical Study.
ChemInform, 2012Co-Authors: Elena A. Pritchina, Matthew S. Platz, Daria S Terpilovskaya, Yuri P Tsentalovich, Nina P GritsanAbstract:The photochemistry of S4N4 with a highly symmetric cage structure is studied by laser Flash Photolysis and B3LYP quantum chemical computations.
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direct detection of a transient oxenium ion in water generated by laser Flash Photolysis
Journal of the American Chemical Society, 2007Co-Authors: Yueting Wang, Matthew S. Platz, Jin Wang, Michael NovakAbstract:Laser Flash Photolysis of the quinol ester 2b in O2-saturated aqueous phosphate buffer at pH 7.1 with excitation at 266 nm generates a transient intermediate with λmax 460 nm that decays in a first-order manner with an aqueous solution lifetime of (170 ± 10) ns at 22 °C. This intermediate is not affected by O2, but reacts rapidly with N3- with an apparently diffusion-limited rate constant of (6.6 ± 0.2) × 109 M-1 s-1. Steady state Photolysis of 2b yields the quinol 3b as a major reaction product with a yield of ca. 30−35% after correction for photolytic decomposition of 3b. This is the same product that is quantitatively produced by hydrolysis of 2b in the dark. Photolysis of 2b in the presence of 40 mM N3- completely suppresses the yield of 3b The photolytic intermediate is identified as the aryloxenium ion 1b, that was previously indirectly detected by N3--trapping during the hydrolysis of 2b, based on the chemical behavior of the transient and the quantitative agreement of the N3-/solvent selectivity r...
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on the electrophilicity of hydroxyl radical a laser Flash Photolysis and computational study
Journal of the American Chemical Society, 2005Co-Authors: Matthew P Dematteo, Christopher M Hadad, James S Poole, Xiaofeng Shi, Rakesh Sachdeva, Patrick G Hatcher, Matthew S. PlatzAbstract:The rate coefficients for reactions of hydroxyl radical with aromatic hydrocarbons were measured in acetonitrile using a novel laser Flash Photolysis method. Comparison of kinetic data obtained in acetonitrile with those obtained in aqueous solution demonstrates an unexpected solvent effect on the reactivity of hydroxyl radical. In particular, reactions of hydroxyl radical with benzene were faster in water than in acetonitrile, and by a significant factor of 65. Computational studies, at the B3LYP and CBS-QB3 levels, have confirmed the rate enhancement of hydroxyl radical addition to benzene via calculation of the transition states in the presence of explicit solvent molecules as well as a continuum dielectric field. The origin of the rate enhancement lies entirely in the structures of the transition states and not in the pre-reactive complexes. The calculations reveal that the hydroxyl radical moiety becomes more anionic in the transition state and, therefore, looks more like hydroxide anion. In the tran...
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reaction of hydroxyl radical with aromatic hydrocarbons in nonaqueous solutions a laser Flash Photolysis study in acetonitrile
Journal of Physical Chemistry A, 2005Co-Authors: James S Poole, Christopher M Hadad, Xiaofeng Shi, Matthew S. PlatzAbstract:Laser Flash Photolysis (LFP) of acetonitrile solutions of N-hydroxypyridin-2-thione in the presence of trans-stilbene generates a transient absorbance at 392 nm, attributed to the addition of hydroxyl radical to stilbene. The observed transient absorbance was used in competitive LFP experiments to determine relative rates of reaction for hydroxyl radical with a range of aromatic hydrocarbons in acetonitrile. Structure−reactivity relationships for the reaction of hydroxyl radical with arenes are derived. With these aromatic hydrocarbons, we observe a good correlation between the rates of hydroxyl-radical reaction and the ionization potential of the arene. Kinetic isotope effects are consistent with hydroxyl-radical addition being the dominant reaction pathway with the arene.
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laser Flash Photolysis study of methyl derivatives of phenyl azide
Journal of Physical Chemistry A, 1999Co-Authors: Nina P Gritsan, Anna D Gudmundsdottir, Dean Tigelaar, Matthew S. PlatzAbstract:Laser Flash Photolysis (Nd:YAG, 35 ps, 266 nm, 10 mJ; KrF excimer, 249 nm, 12 ns, 70 mJ; XeCl excimer, 308 nm, 17 ns, 50 mJ) of methyl substituted phenyl azides produces the corresponding singlet nitrenes. The singlet nitrenes were detected directly, and their decay was analyzed to yield the observed rate constant kOBS. The observed rate constant is the sum of kR + kISC where kR is the absolute rate constant of rearrangement to an azirine and kISC is the absolute rate constant of intersystem crossing. Values of kOBS were measured as a function of temperature and dissected assuming that kISC is temperature-independent. It was shown that kISC is independent of temperature for 2,6-dimethyl- and 2,4,6-trimethylphenyl singlet nitrenes. The barriers to rearrangement of singlet phenylnitrene, p-methylphenylnitrene, o-methylphenylnitrene, 2,6-dimethylphenylnitrene, and 2,4,6-trimethylphenylnitrene in hydrocarbon solvents are found to be 5.6, 5.8, 5.3, 7.0, and 7.3 ± 0.4 kcal/mol, respectively. The data demonstrat...
Nina P Gritsan - One of the best experts on this subject based on the ideXlab platform.
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Photochemistry of Tetrasulfur Tetranitride: Laser Flash Photolysis and Quantum Chemical Study.
ChemInform, 2012Co-Authors: Elena A. Pritchina, Matthew S. Platz, Daria S Terpilovskaya, Yuri P Tsentalovich, Nina P GritsanAbstract:The photochemistry of S4N4 with a highly symmetric cage structure is studied by laser Flash Photolysis and B3LYP quantum chemical computations.
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photochemistry of tetrasulfur tetranitride laser Flash Photolysis and quantum chemical study
Inorganic Chemistry, 2012Co-Authors: Elena A. Pritchina, Daria S Terpilovskaya, Yuri P Tsentalovich, Nina P GritsanAbstract:The photochemistry of tetrasulfur tetranitride (1) was studied in hexane solution by the laser Flash Photolysis technique (LFP). The experimental findings were interpreted using the results of previous matrix isolation studies (Pritchina, E.A.; Gritsan, N.P.; Bally, T.; Zibarev, A.V. Inorg. Chem.2009, 48, 4075) and high-level quantum chemical calculations. LFP produces two primary intermediates, one of which is the boat-shaped 8-membered cyclic compound (2) and the other is the 6-membered S3N3 cyclic compound carrying an exocyclic (S)–N═S group (3). The primary products 2 and 3 absorb a second photon and undergo transformation to the 6-membered S3N3 cycle carrying an exocyclic (N)–S≡N group (4), which is very unstable and converts back to intermediate 3. The quantum yield of the primary product formation is close to unity even though the quantum yield of photodegradation of 1 is low (∼0.01). Thus, 1 is a photochromic compound undergoing in solution the thermally reversible photochemical isomerization. The...
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Photochemistry of Tetrasulfur Tetranitride: Laser Flash Photolysis and Quantum Chemical Study
2012Co-Authors: Elena A. Pritchina, Daria S Terpilovskaya, Yuri P Tsentalovich, Nina P GritsanAbstract:The photochemistry of tetrasulfur tetranitride (1) was studied in hexane solution by the laser Flash Photolysis technique (LFP). The experimental findings were interpreted using the results of previous matrix isolation studies (Pritchina, E.A.; Gritsan, N.P.; Bally, T.; Zibarev, A.V. Inorg. Chem. 2009, 48, 4075) and high-level quantum chemical calculations. LFP produces two primary intermediates, one of which is the boat-shaped 8-membered cyclic compound (2) and the other is the 6-membered S3N3 cyclic compound carrying an exocyclic (S)–NS group (3). The primary products 2 and 3 absorb a second photon and undergo transformation to the 6-membered S3N3 cycle carrying an exocyclic (N)–SN group (4), which is very unstable and converts back to intermediate 3. The quantum yield of the primary product formation is close to unity even though the quantum yield of photodegradation of 1 is low (∼0.01). Thus, 1 is a photochromic compound undergoing in solution the thermally reversible photochemical isomerization. The mechanism of the photochromic process was established, and the rate constants of the elementary reactions were measured
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laser Flash Photolysis study of methyl derivatives of phenyl azide
Journal of Physical Chemistry A, 1999Co-Authors: Nina P Gritsan, Anna D Gudmundsdottir, Dean Tigelaar, Matthew S. PlatzAbstract:Laser Flash Photolysis (Nd:YAG, 35 ps, 266 nm, 10 mJ; KrF excimer, 249 nm, 12 ns, 70 mJ; XeCl excimer, 308 nm, 17 ns, 50 mJ) of methyl substituted phenyl azides produces the corresponding singlet nitrenes. The singlet nitrenes were detected directly, and their decay was analyzed to yield the observed rate constant kOBS. The observed rate constant is the sum of kR + kISC where kR is the absolute rate constant of rearrangement to an azirine and kISC is the absolute rate constant of intersystem crossing. Values of kOBS were measured as a function of temperature and dissected assuming that kISC is temperature-independent. It was shown that kISC is independent of temperature for 2,6-dimethyl- and 2,4,6-trimethylphenyl singlet nitrenes. The barriers to rearrangement of singlet phenylnitrene, p-methylphenylnitrene, o-methylphenylnitrene, 2,6-dimethylphenylnitrene, and 2,4,6-trimethylphenylnitrene in hydrocarbon solvents are found to be 5.6, 5.8, 5.3, 7.0, and 7.3 ± 0.4 kcal/mol, respectively. The data demonstrat...
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laser Flash Photolysis and computational study of singlet phenylnitrene
Journal of the American Chemical Society, 1999Co-Authors: Nina P Gritsan, Zhendong Zhu, Christopher M Hadad, Matthew S. PlatzAbstract:Laser Flash Photolysis (LFP, Nd:YAG laser, 35 ps, 266 nm, 10 mJ) of phenyl azide (PA) releases open-shell singlet phenylnitrene (1PN). 1PN has a sharp absorption band at 350 nm and a very weak absorption band at 540 nm. These bands are assigned as nz−ny and a mixture of 52% π−nx and 28% nx−π* transitions, respectively, on the basis of CASSCF and CASPT2 calculations. A CASPT2 calculation of the spectrum of triplet phenylnitrene (3PN) is in very good agreement with the experimental spectrum. A sharp absorption band of 3PN at 308 nm and a broad, structured band at 370 nm are assigned as nz−ny and π−π transitions on the basis of CASSCF and CASPT2 calculations. The low intensity, long wavelength band of 3PN tailing to 500 nm is assigned as a mixture of π−nx, nx−π* transitions. The decay of 1PN in pentane was measured as a function of temperature to obtain observed rate constants of disappearance, kobs. The rate constant kobs is equal to kR + kISC, where kR is the absolute rate constant of rearrangement of 1PN ...