Solid-state Photolysis Research Articles

Photoinduced transformation of (Bu4N)2[Pt(NO3)6] complex in the solid state

The solid state photolysis of (Bu4N)2[Pt(NO3)6] salt, accompanied by sharp changing of the colour from light-yellow to brown and green is investigated by a combination of techniques such as electronic paramagnetic resonance, infrared spectroscopy, Raman spectroscopy, and diffuse reflectance spectroscopy. A paramagnetic Pt(III) complex [Pt(NO3)5] 2− is shown to be a product of photolysis at 455 nm and shorter wavelength sources generated due to reduction of Pt(IV) centres with the elimination of the reactive nitrate-radical. Prolonged irradiation or aging in the dark results in the formation of mixed-valence Pt(III)-Pt(IV) species from trapped [Pt(NO3)5] 2− and [Pt(NO3)6]2− anions of the host structure. The obtained experimental results are supplemented and compared with the data of density functional theory (DFT) calculations, which allows suggesting a possible mechanism of the studied process.

Photo release of nitrous oxide from the hyponitrite ion studied by infrared spectroscopy. Evidence for the generation of a cobalt-N2O complex. Experimental and DFT calculations

The solid state photolysis of sodium, silver and thallium hyponitrite (M2N2O2, M=Na, Ag, Tl) salts and a binuclear complex of cobalt bridged by hyponitrite ([Co(NH3)5-N(O)-NO-Co(NH3)5]4+) were studied by irradiation with visible and UV light in the electronic absorption region. The UV–visible spectra for free hyponitrite ion and binuclear complex of cobalt were interpreted in terms of Density Functional Theory calculations in order to explain photolysis behavior.The photolysis of each compound depends selectively on the irradiation wavelength. Irradiation with 340–460nm light and with the 488nm laser line generates photolysis only in silver and thallium hyponitrite salts, while 253.7nm light photolyzed all the studied compounds.Infrared spectroscopy was used to follow the photolysis process and to identify the generated products. Remarkably, gaseous N2O was detected after photolysis in the infrared spectra of sodium, silver, and thallium hyponitrite KBr pellets. The spectra for [Co(NH3)5-N(O)-NO-Co(NH3)5]4+ suggest that one cobalt ion remains bonded to N2O from which the generation of a [(NH3)5CoNNO]+3 complex is inferred. Density Functional Theory (DFT) based calculations confirm the stability of this last complex and provide the theoretical data which are used in the interpretation of the electronic spectra of the hyponitrite ion and the cobalt binuclear complex and thus in the elucidation of their photolysis behavior.Carbonate ion is also detected after photolysis in all studied compounds, presumably due to the reaction of atmospheric CO2 with the microcrystal surface reaction products. Kinetic measurements for the photolysis of the binuclear complex suggest a first order law for the intensity decay of the hyponitrite IR bands and for the intensity increase in the N2O generation. Predicted and experimental data are in very good agreement.

Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

Surface processes and radical chemistry within interstellar ices are increasingly suspected to play an important role in the formation of complex organic molecules (COMs) observed in several astrophysical regions and cometary environments. We present new laboratory experiments on the low-temperature solid state formation of complex organic molecules – glycolaldehyde, ethylene glycol, and polyoxymethylene – through radical-induced reactivity from VUV photolysis of formaldehyde in water-free and water-dominated ices. Radical reactivity and endogenous formation of COMs were monitored in situ via infrared spectroscopy in the solid state and post photolysis with temperature programmed desorption (TPD) using a quadripole mass spectrometer. We show the ability of free radicals to be stored when formed at low temperature in water-dominated ices, and to react with other radicals or on double bonds of unsaturated molecules when the temperature increases. It experimentally confirms the role of thermal diffusion in radical reactivity. We propose a new pathway for formaldehyde polymerisation induced by HCO radicals that might explain some observations made by the Ptolemy instrument on board the Rosetta lander Philae. In addition, our results seem to indicate that H-atom additions on H2 CO proceed preferentially through CH2 OH intermediate radicals rather than the CH3 O radical.

The chromatographic approach to kinetic studies of tebipenem pivoxil.

A validated high-performance liquid chromatography-diode array detector (HPLC-DAD) method for stability studies of tebipenem pivoxil was developed. The separation of tebipenem pivoxil in the presence of main degradation product—tebipenem—was achieved by using a LiChrospher C-18 column (5 µm, 250 × 4.6 mm) with the mobile phase containing a mixture of 50 mmol L(-1) ammonium acetate-acetonitrile-triethylamine (68 : 30 : 2, v/v/v) adjusted to pH 3.5 with concentrated phosphoric acid (V). The column effluent was monitored by a photodiode array detector at 330 nm. The flow rate was 0.8 mL min(-1). Tebipenem pivoxil was subjected to degradation in aqueous solutions (acid-base hydrolysis, oxidation) and in the solid state (photolysis, thermolysis at an increased relative humidity and in dry air). The validated HPLC method was successfully applied to investigate the kinetics of conversion of tebipenem pivoxil to tebipenem (main metabolite). The other degradation products of tebipenem pivoxil were also monitored.

Tebipenem pivoxyl. Derivative spectroscopy study of stability of the first oral carbapenem

A simple and selective derivative spectrophotometric method was developed for the quantitative determination of tebipenem and its pivoxyl ester in the presence of degradation products formed during degradation in aqueous solutions (hydrolysis, oxidation, phosphate buffer pH ∼6.0) and in the solid state (photolysis, thermolysis in dry air and at an increased relative air humidity). The method was based on zero-crossing first-derivative spectrophotometry (λ=341nm for tebipenem pivoxyl and λ=320nm for tebipenem), which eliminated the overlapping caused by various degradation products. The selectivity of the method for determination of tebipenem pivoxyl and tepipenem during stability studies was an effect of lack of substituents containing π-bond system chromophores in degradation products. It was also confirmed by comparison of the experimental spectra sample with the theoretical UV spectra and their first derivatives which were obtained by using the density functional theory with the B3LYP hybrid functional and 6-31G(d,p) basis set. The method were linear in the concentration range 16.70–220.0μgmL−1 for tebipenem (λ=320nm; r=0.9989) and 10.70–160.0μgmL−1 for tebipenem pivoxyl (λ=341nm, r=0.9990). The limits of detection and quantitation were 4.72 and 15.60μgmL−1 for tebipenem and 2.54 and 8.40μgmL−1 for tebipenem pivoxyl, respectively. The method had a good intra-day precision (RSD from 0.12% to 0.62%) and inter-day precision (RSD from 0.22% to 2.13%). The recovery of tebipenem and tebipenem pivoxyl ranged from 99.61% to 99.86% and from 99.38% to 99.87%, respectively. First-derivative spectrophotometry was used for a routine analysis of tebipenem and its ester as well as to monitor the conversion of tebipenem pivoxyl to tebipenem and to predict their degradation pathways.

Crystal structures and photoreactivity of trans- and cis-valerophenone diperoxides

AbstractThe crystal structures of valerophenone diperoxides trans-1 and cis-1 were elucidated by X-ray crystallographic analysis. The 1,2,4,5-tetraoxane rings of both compounds adopt chair conformations. Intermolecular CH···O hydrogen bond, π–π, and CH/π interactions exist in cis-1, whereas only CH/π interactions exist in trans-1. In the asymmetric unit of the crystal, a half molecule exists for trans-1, while one molecule for cis-1 which shows whole-molecule disorder. Solid-state photolysis (at 254 nm) or solution-state thermolysis (at 150 °C) of trans-1 and cis-1 produced valerophenone (2) and butyl benzoate (3). Rationalization of the solid-state photoreactivity of the diperoxides by their crystal structures was attempted.Index abstractThe crystal structure of cis-valerophenone diperoxide (cis-1) shows whole molecule disorder. Its lower photoreactivity in the solid state is explained by the locally narrow and rigid reaction cavity due to the Ph–Ph π–π overlap.[IMAGE]

ChemInform Abstract: Solid State Photolysis of Triazene 1-Oxides with Naphthols. Synthesis of Azo Dyes.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Controllable Selective Functionalization of a Cavitand via Solid State Photolysis of an Encapsulated Phenyl Azide

Phenyl azide (1) has been encapsulated within cavitand 2 to form a 1:1 complex of 1@2 in the solid state. Subsequent irradiation affords two diastereomeric nitrene addition products 5 and 7. The ratio of 5 and 7 can be reversed by thermally induced valence isomerization to 1H-azepine 8 followed by photolysis. In sharp contrast, phenylnitrene generation by photolysis of the corresponding 1.5:1 complex results mainly in the regioselective formation of C-H insertion product 4. The supramolecular approach to phenylnitrene chemistry provides good yields, in contrast to the generally low yield reactions of this species in solution.

Chlorine Photoelimination from a Diplatinum Core: Circumventing the Back Reaction

The d(9)...d(9) Pt(2)(I,I)(tfepma)(2)Cl(2) (1) compound (tfepma = ((CF(3)CH(2)O)(2)P)(2)NCH(3)), d(7)-d(9) Pt(2)(I,III)(tfepma)(2)Cl(4) (2) and d(7)-d(7) Pt(2)(III,III)(tfepma)(2)Cl(6) (3), homologous suite of compounds have been prepared. Irradiation of 3 with visible light generates 2 in solution in the presence of 2,3-dimethyl-1,3-butadiene with a quantum efficiency of approximately 38%. The evolution of Cl(2) upon solid-state photolysis of 3 represents the first example of the thermodynamically unfavorable halogen elimination without the use of a chemical trap.

Photocyclization of 2,4,6-triethylbenzophenones in the solid state

Photocyclization of 2,4,6-triethylbenzophenones (TEBPs) into ( E)- or ( Z)-benzocyclobutenols (( E)- or ( Z)-CBs) is E-selective in solution. By contrast, upon solid-state photolysis, TEBP-3,4-diCl and especially TEBP-4- t-Bu gave ( Z)-CB relative to ( E)-CB with a much higher proportion than that in solution. For TEBP-4- t-Bu, the most major product in the solid state is an indanol derivative (Inol) ( E/ Z/Inol=1:3.9:10.3 at 9% conversion). On the basis of the X-ray crystallographic analysis, Inol and ( Z)-CB are both topochemical products. Notably, the relative proportion of ( E)-CB increased with increased conversion, namely with increased disruption of the crystal lattice. The DFT calculation of highly hindered 2,6-diisopropylbenzophenone (DIBP) was also conducted. These results in conjunction with the previous results on 2,4,6-triisopropylbenzophenones (TIBPs) indicate that CB is formed either via trans-enol followed by its conrotatory ring-closure (paths a and d) or through direct cyclization of biradical (BR) (path b) as shown in Scheme 1. Normally the former route is faster. However, in the crystalline state or in the case of sterically hindered phenyl ketones, path b tends to be adopted.

Orbital-Overlap Control in the Solid-State Reactivity of β-Azido-Propiophenones: Selective Formation ofcis-Azo-Dimers

Solid-state photolysis of 1a,b yields selectively cis-3a,b. X-ray analysis of 1a,b reveals the molecules adopt an extended structure and as such the crystal packing arrangement consists of planar, pi-stacked molecules. The shortest intermolecular distance between adjacent N-atoms is approximately 3.76 A and would lead to formation of trans-3a,b, whereas cis-3a,b is formed by dimerization between N-atoms that are approximately 3.9 A apart. We propose that the molecular orbital alignment of the adjacent nitrenes controls the solid-state reactivity.

Direct and sensitised photolysis of dispersed photoacid generators to formulate water-borne photopolymers

Casting a photopolymer solution to form a film, followed by image-wise photoirradiation and subsequent wet development, leads to photolithography. Whereas the wet development is achievable with aqueous alkali, the emission of an organic solvent as a volatile organic compound (VOC) is usually inevitable during the film casting because ingredients of common photopolymers are insoluble in water. This work proposes water-borne photopolymers cast and developed solely with neutral water by incorporating mechanically milled sub-micron particles of poorly water-soluble photoacid generators (PAGs), which undergo direct and sensitised solid-state photolysis to make a poly(vinyl alcohol) film insoluble in water with the aid of acid-sensitive crosslinkers. The sensitised solid-state photolysis of onium-type PAGs in the solid state was studied in detail to extend the spectral sensitivity of this kind of photopolymer. Fluorescence quenching measurements revealed that the solid-state sensitisation occurs through singlet exciton migration in sensitiser particles followed by electron transfer to PAG particles at the solid–solid boundary region. Three-component photopolymers comprised of an aqueous dispersion of PAG in the absence or in the presence of a co-milled sensitiser, poly(vinyl alcohol) and a water-soluble diepoxy were formulated to display photosensitivity of 17 mJ cm−2 by the direct photolysis of a dispersed sulfonium salt and that of ca. 120 mJ cm−2, for instance, by the photolysis of an iodonium salt sensitised with co-milled 9,10-dipropoxyanthracene.

Norrish Type I vs. Norrish-Yang Type II in the Solid State Photochemistry of CIS-2,6-DI(1-Cyclohexenyl)-Cyclohexanone: A Computational Study

A computational study of the reaction mechanism for the solid state photolysis of cis-2,6-di(1-cyclohexenyl)cyclohexanone ( 1 ) was carried out using density functional theory. Compound 1 was designed to explore the competition between several possible pathways, but mainly to discern from α-cleavage/decarbonylation (Norrish type I), and γ-hydrogen abstraction followed by cyclization (Norrish type II- Yang). The triplet state reaction coordinates for the type I and II photochemistry were obtained computationally. While calculations predict that the type I reaction should be predominant in the triplet state due to lower barrier heights for the process, the observed reactivity in the solid state favored the type II process. By correlating the results from calculations and experiments with singlet/triplet sensitizers/quenchers, it was found that the observed reactivity takes place along the singlet manifold.

Solid-State Photolysis of α-Azidoacetophenones

Solid-state photolysis of 1 yields 2 in a crystal-to-crystal reaction. The reaction takes place by alpha-cleavage to form a benzoyl and an azido alkyl radical pair. The azido alkyl radicals rearrange into iminyl radicals and N2. The iminyl and benzoyl radicals are held in close proximity within the crystal lattice, which allows them to combine and form 2. X-ray structure analysis, molecular modeling and trapping studies support this mechanism.

Solid-state diphotocyclization of iso- and terephthalaldehydes via dihalogen substitution.

The supramolecular nonbonded C-H...X interactions between formyl hydrogens and ortho-halogen atoms (Br/Cl) have been exploited to achieve conformational control in the solid state of dimethyl-substituted iso- and terephthaladehydes (1-3) for unprecedented diphotocyclization. It is shown that the dihalogen substitution also contributes to the stability of the benzocyclobutenols relative to their precursor photoenols, so that the solid-state photolysis of dialdehydes 2b, 2c, and 3b leads to diphotocyclization to afford respectable yields of bis-benzocyclobutenols.

Intermediate reactions in solid-state photolysis

Photodissociation of impurity-doped solids involving chemical reactions with host atoms is experimentally studied. We demonstrate that the formation of intermediate molecules (HKrCl) plays a central role in the photodissociation of HCl in solid Kr, developing considerably the general understanding of solid-state photolysis dynamics. In addition, these experiments provide a quantitative test for the ab initio calculations of IR absorption intensities of novel rare-gas molecules. The measured UV absorption spectrum of HKrCl is valuable for characterizing the electronically excited states of rare-gas containing species, which is a significant challenge to theory.

Solid-state photochromism and photoreactivity of o- and p-anisaldehydes. Remarkable stabilization of o-xylylenols.

[reaction: see text] All of the crystalline o-anisaldehyde derivatives 1 and 3 change to brick-red color upon brief exposure to UV-vis radiation. The red color, attributed to (E)-xylylenol, is remarkably persistent for hours (ca. 10 h) in the case of 1c; such a long lifetime for the reactive o-xylylenols is unprecedented. In contrast, the p-anisaldehydes 2 undergo cyclization. Solid-state photolysis of 2b affords the benzocyclobutenol 7b regioselectively, which is not accessible from solution-phase photolysis.

Solid-state photolysis of sterically congested cis-1,2-dibenzoylalkenes: isolation and characterization of vinylketenes

Hitherto non-isolable vinylketenes from the solid state photolysis of cis-1,2-dibenzoylalkene compounds have been isolated and characterized and their stabilities were found to be enhanced with the extent of steric congestion in the molecules.

Solid-State Photolysis of Anthracene-Linked Ammonium Salts: The Search for Topochemical Anthracene Photodimerizations

The reaction of 9-N,N-dimethylaminomethylanthracene 1 with aromatic carboxylic acids gave crystalline salts (2a, 2b, 3a and 3b), which were irradiated in the solid state. Whereas salt 3a was selectively transformed to the dimer 4a, the other salts were photoinert. The results were rationalized on the basis of X-ray structure analysis. In the presence of oxygen, solid-state irrradiation of anthracene salt 3b leads to selective photooxygenation. The selectivity of both solid-state photoreactions was not observed in solution.

Formation and characterization of neutral krypton and xenon hydrides in low-temperature matrices

A family of rare-gas-containing hydrides HXY (where X=Kr or Xe, and Y is an electronegative fragment) is described. These molecules are experimentally prepared in low-temperature matrices by photodissociation of a hydrogen-containing HY precursor and thermal mobilization of the photodetached hydrogen atoms. The neutral HXY molecules are formed in a concerted reaction H+Y→HXY. Experimental evidence for the formation of these species is essentially based on strong infrared absorption bands that appear after annealing of the photolyzed matrices and are assigned to the H-X stretch of the HXY molecules. Computationally, the formation of these HXY molecules decreases the H-X distance by a factor of ⩾2 from its van der Waals value, which emphasizes their true chemical bonding, possessing both covalent and ionic contributions. The estimated dissociation energies vary from 0.4 to 1.4 eV and hold promise for forthcoming observation of these molecules in the gas phase. The experiments with the HXY molecules widen our knowledge on solid-state photolysis dynamics of hydrogen-containing species. In particular, the photolysis of small HY hydrides in solid Xe seems to be a quite local process, and the accompanying losses of H atoms play a minor role.