Final Photolysis Products Research Articles

Photochemistry of IrCl<sub>6</sub><sup>3–</sup> complex in aqueous solutions

The photochemistry of the [IrIIICl6]3- complex in aqueous solutions was studied by the methods of stationary and laser flash photolysis. As the result of a light quantum absorption, parallel processes of photoaquatation and photoionization occur. The aquated electron ea–q, which is formed with a quantum yield of 0.12 (excitation at 266 nm), is predominantly decayed in reactions with the initial complex and dissolved oxygen. The rate constant of ea–q capture by the [IrIIICl6]3- complex was measured. The main final photolysis products are Ir(III) complexes with different compositions of ligands, as well as several percents of Ir(IV) complexes. The formation of final products occurs in the time range from milliseconds to seconds.

Studying manganese carbonyl photochemistry in a permanently porous metal-organic framework.

Mn(diimine)(CO)3X (X = halide) complexes are critical components of chromophores, photo- and electrocatalysts, and photoactive CO-releasing molecules (photoCORMs). While these entities have been incorporated into metal-organic frameworks (MOFs), a detailed understanding of the photochemical and chemical processes that occur in a permanently porous support is lacking. Here we site-isolate and study the photochemistry of a Mn(diimine)(CO)3Br moiety anchored within a permanently porous MOF support, allowing for not only the photo-liberation of CO from the metal but also its escape from the MOF crystals. In addition, the high crystallinity and structural flexibility of the MOF allows crystallographic snapshots of the photolysis products to be obtained. We report these photo-crystallographic studies in the presence of coordinating solvents, THF and acetonitrile, showing the changing coordination environment of the Mn species as CO loss proceeds. Using time resolved experiments, we report complementary spectroscopic studies of the photolysis chemistry and characterize the final photolysis product as a possible Mn(ii) entity. These studies inform the chemistry that occurs in MOF-based photoCORMs and where these moieties are employed as catalysts.

A facile synthesis of Cu(II) diethyldithiocarbamate from monovalent copper-cysteamine and disulfiram

An efficient, atom-economic synthesis of Cu(II) diethyldithiocarbamate from a monovalent copper-cysteamine and disulfiram was developed. • An efficient and atom-economic synthesis of Cu(DDC)2 from DSF and monovalent copper cysteamine (CuCy) is reported. • The chemical structure, proposed reaction mechanism and the optimal reaction conditions were investigated. • The photochemical reactions of Cu(DDC) 2 in five solvents and the possible reaction mechanism were discussed. The copper(II) diethyldithiocarbamate (Cu(DDC) 2 ) complex prepared from disulfiram and Cu(II) species has shown excellent anticancer activity. However, general synthetic methods largely rely on tedious procedures and limited reaction types with undesirable by-products. In this paper, we reported an efficient and atom-economic synthesis of Cu(DDC) 2 from disulfiram and monovalent copper cysteamine (Cu(I)Cy) via a one-step oxidation–reduction reaction. Cu(DDC) 2 was fully characterized by nuclear magnetic resonance (NMR), mass spectrometry (MS), infrared spectroscopy (IR), scanning electron microscope (SEM), X-ray diffraction (XRD), ultraviolet and visible (UV–Vis) spectrophotometry, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and single crystal X-ray diffraction. The proposed reaction mechanism and the effect of reaction conditions on the Cu(DDC) 2 synthesis were investigated. The photochemical reactions of Cu(DDC) 2 was studied in acetone, DMF, toluene, CCl 4 , CHCl 3 under 254, 365 nm alone or combined 254 & 365 nm irradiation based on UV–vis and EPR measurements. The photolysis rate followed in this order: CCl 4 > CHCl 3 > DMF > toluene > acetone. The final photolysis products in CHCl 3 were DSF and Cu 2 (DDC) 2 Cl 2 .

Elementary Stages of Photochemical Reactions of Substituted 2,6-Diphenyl-para-benzoquinones with Thiols

Using the effects of chemical polarization of nuclei, mechanism and elementary stages of photochemical reduction of 2,6-diphenyl-1,4-benzoquinone with thiols have been elucidated. The studied quinone is reduced with ethanethiol in two stages (transfer of electron followed by proton transfer). The final photolysis product is a derivative of dibenzofuran.

Photolysis of Carbon Disulfide by Interior Microwave Discharge Electrodeless Iodine Lamps

AbstractThis study presents interior microwave discharge electrodeless iodine lamps (IMDEL-I2) that assist the photodegradation of CS2 at room temperature and atmospheric pressure. The investigation examined the photolysis efficiency of CS2, the absolute removal amount (ARA), and the energy yield (EY) under different gas residence times and input powers and also included an analysis of the photodegradation products of CS2. The experimental results indicated that the IMDEL-I2 was capable of emitting ultraviolet (UV) radiation in bands of 206.2, 250–350, and 385–400 nm, and vacuum ultraviolet (VUV) light at 178.3, 180.1, 183, 184.4, and 187.6 nm. The photodegradation rate of CS2 in the IMDEL-I2 system was 93.4%, with ARA of 18.1 mg/s and EY of 82.5 mg/kWh at the gas retention time of 1.98 s, an input power of 796 W, and an initial concentration of 85.6 mg/m3. The final photolysis products of CS2 were identified to be SO2, CO2, CO, and COS in the gaseous phase, and (CS)n, SO42−, and sulfur in the solid phase.

Photochemical reactivity of the iron(III) complex of a mixed-donor, α-hydroxy acid-containing chelate and its biological relevance to photoactive marine siderophores.

The trimeric clusters [Fe(III)3(X-Sal-AHA)3(μ3-OCH3)](-), where X-Sal-AHA is a tetradentate chelate incorporating an α-hydroxy acid moiety (AHA) and a salicylidene moiety (X-Sal with X being 5-NO2, 3,5-diCl, all-H, 3-OCH3, or 3,5-di-t-Bu substituents on the phenolate ring), undergo a photochemical reaction resulting in reduction of two Fe(III) to Fe(II) for each AHA group that is oxidatively cleaved. However, photolysis of structurally analogous mixed Fe/Ga clusters demonstrate that a similar photolysis reaction will occur with only a single Fe(III) in the cluster. Quantum yields of iron reduction for the series of [Fe(III)3(X-Sal-AHA)3(μ3-OCH3)](-) complexes measured by monitoring Fe(II) production are twice those for ligand oxidation, measured by loss of the CD signal for the complex due to cleavage of the chiral AHA group.The quantum yields, 2-13% in the UVA and UVB ranges, are higher for complexes with electron-withdrawing X groups than for those with electron-donating X groups [corrected]. The observed final photolysis product of the chelate is different if irradiation is done in the air than if it is done under Ar. The first observed photochemical product is the aldehyde resulting from decarboxylation of the AHA. This is the final product under anaerobic conditions. In air, this is followed by an Fe- and O2-dependent reaction oxidizing the aldehyde to the corresponding carboxylate, then a second Fe- and light-dependent decarboxylation reaction giving a product that is two carbons smaller than the initial ligand. These reactivity studies have important biological implications for the photoactive marine siderophores. They suggest that different types of photochemical products for different siderophore structure types do not result from different initial photochemical steps, but rather from different susceptibility of the initial photochemical product to air oxidation.

Generation of oxidative species from ultraviolet light induced photolysis of fructose

Fructose has shown significant reactivity during ultraviolet light (UV, 254nm) processing of fruit juices that can adversely affect product quality. The present study demonstrates that this reactivity of fructose is due to the oxidative nature of products formed from UV induced photolysis of fructose. This was accomplished using fluorescein, a fluorescent dye that loses fluorescence intensity upon reaction with oxidative species. Fructose caused a concentration dependent decay of fluorescence from fluorescein only in presence of UV, indicating oxidative nature of photolysis products of fructose. The transient oxidative species including free radicals and not one of the final photolysis products, furan, were responsible for fluorescence decay. Addition of an antioxidant and removal of oxygen from solution lowered the rate of fluorescence decay, suggesting strategies that can be employed to lower the deleterious effects of fructose on products. The understanding developed can be used to optimise UV processing of juices.

Rules governing the formation of photolysis products in the lead azide-copper(I) oxide system

It was found that, along with a decrease in the rate of photolysis and photocurrent in the region of lead azide intrinsic absorption, the addition of copper(I) oxide broadened the range of spectral sensitivity, and preliminary treatment of the PbN6(Ab)-Cu2O system with light (λ = 365 nm) increased the rate of photolysis. The rate constants for photolysis were estimated. An analysis of the results of current-voltage characteristic, contact potential difference, and contact photo-electromotive force measurements was used to construct a diagram of energy zones and suggest a model of the photolysis of the PbN6(Ab)-Cu2O system including stages of the generation, recombination, and redistribution of nonequilibrium carriers in a contact field, formation of microheterogeneous PbN6(Ab)-Pb (photolysis product) systems, and formation of final photolysis products.

Photochemical decarboxylation and deacetylation of the cobalt(III) aminocarboxylate complexes: The crystal structure of the [Co(CH2CH2CH2NH2)(En)2)]Br2 and [Co(Bipy)(Cl)(Edma)]Cl · 2H2O photoproducts (En is Ethylenediamine, Bipy is 2,2′-bipyridine, and Edma is ethylenediaminemonoacetate)

The crystals of [Co(CH2CH2CH2NH2)(En)2]Br2 (I) and [Co(Bipy)(Cl)(Edma)]Cl · 2H2O (IIa) (IIa) are studied by X-ray diffraction analysis. Compound I is synthesized by the crystallization of the [Co(En)2(Amb)]2+ primary photolysis products. Compound IIa is synthesized from the [Co(Bipy)(Edda)]+ final photolysis products (En is ethylenediamine; Bipy is 2,2′-bipyridine; Edma and Edda are the anions of ethylenediaminemonoacetic and ethylenediamine-N,N′-diacetic acids, respectively; Amb is the 4-aminobutyrate ion). The crystal structure of complex I indicates the contraction of the seven-membered aminobutyrate CoO2CCH2CH2CH2NH2 ring to the five-membered CoCH2CH2CH2NH2 ring by the photoelimination of the CO2 molecule. The formation of the Co(III) complexes with the Edma ligands upon the photolysis of [Co(Bipy)(Edda)]+ is due to successive reactions of contraction of the five-membered aminoacetate rings and hydrolysis of the Co-C bond.

Different reaction mechanisms of diphenylether and 4-bromodiphenylether with nitrous acid in the 355 nm laser flash photolysis of mixed aqueous solution

The microscopic reaction mechanisms of diphenylether (DPE) and 4-bromodiphenylether (4-BrDPE) with nitrous acid (HNO 2) in the absence of O 2 have been explored by the 355 nm laser flash photolysis. It was proposed that OH radical, from the photolysis of HNO 2, added to DPE forms the C 12H 10O–OH adduct while added to 4-BrDPE forms the 4-BrDPE–OH and 4-BrOH–DPE adducts. The first-order decay rate constants of the C 12H 10O–OH adduct, 4-BrDPE–OH adduct and 4-BrOH–DPE adduct were measured to be (1.86 ± 0.14) × 10 5 s −1, (2.19 ± 0.04) × 10 5 s −1 and (1.56 ± 0.03) × 10 5 s −1, respectively. The final photolysis products of DPE and HNO 2 identified by GC/MS analysis were phenol, o-hydroxydiphenylether, p-hydroxydiphenylether and p-nitrodiphenylether, while the final photolysis product of 4-BrDPE and HNO 2 identified by LC/MS analysis was mainly the dimer.

UV photostability of metal phthalocyanines in organic solvents.

Kinetic studies of photochemical reactions induced by UV radiation in solutions of metal phthalocyanines have been carried out to determine the factors which might have influenced the stability of photosensitized phthalocyanines. Complexes of the molecular type Mpc, M'(2)pc, and Lnpc(2) (where M = Li, Mg, Fe, Co, Zn, Pb; M'= Tl; Ln = rare earth; pc = phthalocyanine ligand, C(32)H(16)N(8)(2-)) were investigated in DMF, DMSO, and pyridine. Progressive decay of the phthalocyanine macrocycle due to absorption of UV light was observed. Phthalimide found in the final photolysis product may indicate some chemically bonded oxygen involved in the solid phthalocyanine material. Fluorescence lifetimes determined for the studied compounds (2.91-5.98 ns) have shown no particular relation to the stability of the excited macrocyclic system. The bonding strength of the photosensitized phthalocyanine moiety appears to rely on typical chemical factors, rather than on the properties of the excited states. Kinetics of the degradation process has proved to depend on the molecular structure of the complex and seems to be controlled by interactions of the macrocycle bridging nitrogen atoms with the solvent molecules. The use of electron acceptor solvents such as DMSO may enhance the molecular stability of phthalocyanines excited by UV radiation. Sandwich-type rare earth diphthalocyanines dissolved in DMSO displayed the highest photostability.

Photochemistry of fac-Pt(NO 2) 3Cl 32− complexes in water solutions

The photochemical transformation of fac-Pt(NO 2) 3Cl 3 2− complex in water solutions and frozen matrices has been studied by laser flash photolysis, optical, ESR, and NMR spectroscopies. Upon steady-state photolysis of liquid water solutions, the fac-Pt(NO 2) 3Cl 3 2− absorption bands disappear in the optical spectrum with both the preservation of isosbestic point at 43 620 cm −1 and the appearance of a new absorption band with a maximum at 48 000 cm −1, belonging to Pt(II) complexes. Applying the NMR method to nuclei 195 Pt and 14 N , we have shown that the final photolysis products are mainly complexes [PtCl 3(NO 2)] 2−, Pt(NO 2) 2(H 2O) 2, and [Pt(NO 2) 6] 2−. The photolysis of frozen (H 2O+LiCl or H 2O+MgClO 4) matrices containing the fac-Pt(NO 2) 3Cl 3 2− complex yields a new wide absorption band with a maximum in a region of 30 000 cm −1 which belongs to the [PtCl 3(NO 2) 2(ONO)] 2− nitrito-isomer of the initial complex. A longer irradiation causes photodissociation of nitrito-isomer into a complex of trivalent platinum [PtCl 3(NO 2) 2] 2− and free NO 2 radical whose characteristic lines are manifested in the ESR spectrum. The laser flash photolysis shows that in solution at room temperature, the [PtCl 3(NO 2) 2(ONO)] 2− nitrito-isomer thermally dissociates in about 300 ns with an activation energy of 48.6±1.7 kJ mol −1. The [PtCl 3(NO 2) 2] 2− complex dissociates in about 7 μs giving the second free NO 2 radical and a [PtCl 3(NO 2)] 2− complex. This reaction has an activation energy of 37.6±1.5 kJ mol −1. It is shown that dissociation of the [PtCl 3(NO 2) 2] 2− complex is reversible and the NO 2 radical coordinates again with the [PtCl 3(NO 2)] 2− ion with a rate constant 4.2×10 9 M −1 s −1. In addition to the repeated coordination, the NO 2 radical also disappears in a reversible reaction of recombination (2 k rec=1.8×10 9 M −1 s −1) to give N 2O 4 molecule.

ArF laser dissociation of trisilane

The laser photolysis of trisilane at 193 nm was studied. The final photolysis products were monosilane, disilane and tetrasilanes. The results were indicative of the participation in the photolysis process of at least two different dissociation pathways which account for about 80% of the total parent molecule dissociation. ArF laser multiphoton dissociation of Si 3H 8 in a free jet expansion was also studied. Photofragment fluorescence from SiH(A 2Δ) and several singlet and triplet excited states of the silicon atom was observed. The rovibrational population distributions in SiH(A 2Δ) were obtained by spectral simulation. The rotational distributions can be characterized by near-Boltzmann distributions. The average rotational energies in ν = 0 and ν = 1 are 1550 and 1140 cm −1 respectively and the average vibrational energy in the observed vibrational levels ( ν = 0–2) is 800 cm −1.

Photoredox chemistry of p-nitrophenylalanine and p-nitrophenethyl amine in basic aqueous solution: formation of an observable long-lived intermediate

The photochemistry of p-nitrophenylalanine ( 1), an artificial amino acid, and p-nitrophenethyl amine ( 2) was studied in aqueous solution over a range of pH. Irradiation of these two compounds in basic solution results in the development of a highly visible orange—red colour which decays slowly over 24 h, indicative of the formation of a long-lived intermediate. Sunlight is effective in inducing this colour change with the more reactive p-nitrophenylalanine. From the structure of the final photolysis product ( p-aminobenzaldehyde ( 5)) and UV—visible and proton nuclear magnetic resonance ( 1H NMR) (360 MHz) studies of the photoreaction, a mechanism is proposed which involves initial electron transfer from the amino group of 1 and 2 to the nitrophenyl triplet excited state, followed by a complex reaction pathway resulting in overall intramolecular redox chemistry.

IR Laser Chemistry of Dimethylnitramine and Diethylnitramine

The infrared multiphoton decomposition of dimethylnitramine and diethylnitramine in the gas phase under almost collisionless conditions has been studied with a tunable CO2 laser. The steady state rate coefficient for their unimolecular decomposition were found to be kDENA(st) = 105.5 ± 0.1(I/MW cm–2) s–1, and kDENA(st) = 105.2 ± 0.1(I/MW cm–2) s–1, for laser intensities in the range 3–15 MW cm –2. The dependence of rate constants and product yields on laser fluence have indicated that the unimolecular dissociation of both nitramines occurs via scission of the N‐NO2 bond, and the main secondary reaction leading to the final photolysis products (nitrosamine and nitroxide) is the oxidation reaction of nascent dialkylamino radical with parent nitramine or NO2 product.

The photochemistry of the aliphatic nitrocompounds

1. The photochemical breakdown of theα-polynitroalkylsulfides (I) andα-polynitroalkylsulfones (II) proceeds largely through homolytic\(C_{NO_2 } - S\) bond rupture with the formation of radicals. 2. The extent of breakdown of (I) and (II) is determined by the molecular structure, being almost completely unaffected by the nature of the solvent. The ratio of the final photolysis products is determined by secondary reactions between the radicals and between the radicals and the solvent.