Anthracene In Solution Research Articles

Transient absorption spectra of aromatic radical cations in hydrocarbon solutions

Hydrocarbon solutions of toluene, naphthalene, acenaphthene, anthracene and pyrene were studied by 248 and 308 nm laser flash photolysis at room temperature. Time profiles of optical absorption and conductivity signals were taken and assigned to the formation and decay of transient radical cations. Biphotonic ionization was observed for all substrates by d.c. conductivity measurements. The overall quantum yields of free ions for the aromatic molecules studied measured by d.c. conductivity (for 248 nm laser flash photolysis) are in the range 1 X 10 −3 to 5 X 10 −3. Absorption spectra of transient radical cations were observed in all cases with the exception of toluene, where strong absorption from the excited singlet state of toluene completely obscured the radical cation signal. Similarly, the absorption of the excited singlet state of naphthalene interferes with the observation of its radical cation.

Basic studies of deactivation of hydrotreating catalysts with anthracene

A sulfided commercial Ni-Mo-P/alumina catalyst was coked in an autoclave reactor at 375°C with solutions of anthracene in mineral oil to give catalysts containing 2–12% C. After extraction and resulfiding, physical properties and catalytic activities using a mixture of model compounds were measured. It was found that the coke was evenly distributed throughout the catalyst particles. All physical properties decreased with increasing coke content. Only a small fraction of pores was blocked by coke. Diffusivity measurements indicated internal pore mouths were constricted by coke. Catalytic activities for hydrodesulfurization (HDS), hydrogenation (HYD) and hydrodenitrogenation (HDN) all decreased with increasing coke content, but not to the same extent, the order of deactivation being: HDS > HYD > HDN. The results are interpreted in terms of a porewedge model of coke deposits.

Study of angular correlation by N.M.R. of magnetically aligned molecules

A theoretical description of angular correlation in N.M.R. of diamagnetically aligned molecules is presented. High field deuterium N.M.R. is employed to study solutions of benzene, naphthalene and anthracene in binary mixtures of cyclohexane and hexafluorobenzene. Strong orientational cross correlation between the aromatic hydrocarbons and hexafluorobenzene is detected.

Microsphere distribution in normal and tumor-bearing (DMBA-induced carcinogenesis) hamster cheek pouch.

This study evaluates, for the first time by direct visualization, the microvascular distribution of microspheres in normal hamster cheek pouch and in hamster cheek pouch bearing tumor induced by 7, 12 Dimethylbenz (A) Anthracene solution (DMBA). In contrast to the results of the previously used open-chest technique, this carotid injection technique does not lead to irregular distribution of 15-mu carbonized microspheres, chain, or impaction phenomena. It is concluded that methodology differences may account for different results.

Raman scattering tensor elements for some ag modes of anthracene

AbstractThe intensities of the Raman lines of anthracene in solution and in the pure crystal at room temperature have been measured using several excitation frequencies (ν0) in the pre‐resonance region. The data were used to derive molecular scattering elements αii at each νo for a number of ag fundamentals. While the values of αxx and αyy are constant over the restricted range of excitation used, αzz shows an enhancement as νo moves towards resonance with the first absorption system (I). Overlap factors were determined from the fluorescence spectrum of anthracene in a biphenyl matrix, and these values were used to calculate the contribution αzz(I) due to scattering off the first excited electronic state. Working beyond the oriented‐gas assumption improved the fit between calculated and observed enhancement. There is a measurable background contribution to αzz due to scattering off higher excited states and this has an opposite algebraic sign from αzz(I) for all ag fundamentals except possibly for the 394 cm−1 mode.

Reactions of cyclododecyl radicals in the pulse radiolysis of solutions of naphthalene and anthracene in liquid cyclododecane

1. It was established by the method of pulse radiolysis of solutions of naphthalene and anthracene in liquid cyclododecane with optical recording of the intermediate particles formed that cyclododecyl radicals form adducts ArH...R (in the absence of oxygen) and ArH...O2...R (in the presence of oxygen) with naphthalene and anthracene, respectively. 2. The rate constants of the formation of adducts ArH...R, their conversion to more stable particles in first-order reactions, as well as the destruction of the adducts ArH...O2...R in second-order reactions, were determined.

Singlet oxygen quenching by stable nitroxy radicals

The quenching mechanism of singlet oxygen luminescence at 1.27 μm by different aliphatic and aromatic nitroxy radicals has been studied. The 1O 2 was generated in solutions of anthracene or protoporphyrin IX by excitation with a 347 nm laser flash. The luminescence quenching rate constants have been found to be about 10 5 – 10 6 M −1 s −1 for aliphatic radicals and about 10 6 – 10 7 M −1 s −1 for aromatic radicals and are weakly dependent upon the nature of the solvent. The maximum value k q = 1.6 × 10 7 M −7 s −1 was obtained for di- tert-butyldiphenyl nitroxide which is characterized by a considerable delocalization of the unpaired electron over the molecular fragment and a lower steric screening of the ▪ centre in comparison with other radicals. From an analysis of the experimental data it has been concluded that 1O 2 quenching by radicals occurs exclusively via the electron exchange interaction in collision complexes.

Exciplex type emission from anthracene doped aggregates of phenanthrene formed in n-hexane frozen solutions

Fluorescence, absorption and fluorescence excitation spectra of concentrated (3 × 10 −4 M) solutions of phenanthrene in frozen n-hexane in the presence of anthracene have been investigated at 77 and 4 K. Decay time analysis of the anthracene sensitized emission reveals the existence of at least two types of superposed emissions. One emission (τ M ≈ 9 ns) is similar to that from solid solutions of anthracene in phenanthrene crystal while the other is structureless and anthracene-concentration dependent (τ M ≈ 30–65 ns). The latter has been assigned to an exciplex type emission from particular anthracene-phenanthrene configurations which occur in very small size phenanthrene pseudocrystallites, imbedded in an n-alkane matrix.

Spectral shifts in the fluorescence spectrum of anthracene under the influence of laser driven shock compression

We report spectral shifts in the fluorescence emission of a solution of anthracene in benzene under the influence of laser driven shock compression. Red-shifts of up to 800 cm −1 are observed in the peak of the 0–1 vibronic band of anthracene corresponding to maximum pressures of =10 kbar. These results are in agreement with literature values of spectral shifts obtained under conditions of high static pressure. Laser driven shock provides an attractive alternative to conventional shock generation schemes when used in conjunction with optical spectroscopy as a probe of molecular level changes.

Solute-Induced Photo-Ionization of Nonpolar Liquids

Transient dc conductivity measurements of anthracene solutions in cyclohexane have provided evidence for solvent ionization following irradiation with 248 nm excimer laser pulses. A mechanism resulting in a cyclohexane cation and an anthracene anion as near neighbors can explain the experimental observations: a high mobility species, 7 to 8 absorbed photons per solute molecule, intensity dependence, and absence of enhanced hydrogen generation. The nature of the high-mobility species is discussed and the contribution of geminate ions to transient dc conductivity measurements is analyzed. A photo-ionization apparatus with 20 ps time resolution is being developed to observe the transient ions spectroscopically. Such a system may enable observation of solute-induced ionization in solvents having normal mobility cations.

Reactivity of Anthracene in Liquid SbCl3 ‐ AlCl3 ‐ N ‐ ( 1 ‐ Butyl ) Pyridinium Chloride Mixtures

Mixtures of and N‐(1‐butyl)pyridinium chloride (BPCl) containing and mixtures containing and were found to be liquid at 25°C. Dilute solutions of anthracene were stable in ternary mixtures containing , but in mixtures containing , anthracene reacted under the influence of the solvent, which behaved as both oxidant and H‐transfer catalyst. The oxidized product was protonated anthracene, which was stable in this melt. The source of protons was provided by hydrogen liberating Scholl condensations combined with the reduction of Sb(III). A part of the hydrogen from Scholl reactions reacted with anthracene to form 9,10‐dihydroanthracene. By contrast, a liquid mixture without , (2:1 mole ratio) proved to be a much less active H‐transfer catalyst than the liquids even though it is a stronger Lewis acid, and it did not induce protonation beyond a trace attributable to protic impurities. The role of impurities in these mixtures was investigated with results that are relevant to earlier investigations of liquid mixtures. An improved procedure for purifying BPCl is described.

β-induced fluorescence spectra of some polynuclear aromatic hydrocarbons

High resolution fluorescence spectra from dilute solutions of anthracene, acenaphthene, chrysene and perylene excited by β particle radiation from a promethium-147 source are reported.

Linear isotherms in multicomponent adsorption onto activated carbon from water and from organic solvents

The linearity and independence of multiple trace components in the presence of a dominant adsorbate, which was previously found for trace liquids on activated carbon in water solution, is also found for solid adsorbates and in organic solvents. This linearity suggests a general method for the determination of multiple trace adsorbates on activated carbon by adsorptive displacement. Systems studied comprise: 2,5-dichlorophenol, 3,5-dichlorophenol, and phenol in aqueous p-nitrophenol; p-nitrotoluene, o-dichlorobenzene, 1,3-dibromopropane, 1-bromohexane, and 2-bromobutane in p-nitrophenol-methanol; and l-chloro-3-nitrobenzene, p-dichlorobenzene, naphthalene, and 1-chloronaphthalene in a cyclohexane solution of anthracene. Isotherms are reported for one, two, and three components.

Kinetics and selectivity of oxidation of saturated hydrocarbons in sulphuric acid media containing anthracene and cyclohexane oligomers

o1.Solutions of anthracene and cyclohexene in 93% sulphuric acid are sources of fairly stable species, which oxidize tertiary and secondary C−H bonds of saturated hydrocarbons at 90°C. A study was made of kinetics and selectivity of the first stage of oxidation of paraffins in these systems.2.The selectivity, isotope effect and kinetics of oxidation of the anthracene-H2SO4 system and oligomers of cyclohexene-H2SO4 are similar and approximate to the oxidizing agent-sulphuric acid systems, previously examined.3.Based on this analogy a mechanism was proposed for the oxidative homolysis of C-H bonds for the first stage of oxidation of saturated hydrocarbons in anthracene-sulphuric acid and cyclohexene-sulphuric acid systems. Solutions of anthracene and cyclohexene in 93% sulphuric acid are sources of fairly stable species, which oxidize tertiary and secondary C−H bonds of saturated hydrocarbons at 90°C. A study was made of kinetics and selectivity of the first stage of oxidation of paraffins in these systems. The selectivity, isotope effect and kinetics of oxidation of the anthracene-H2SO4 system and oligomers of cyclohexene-H2SO4 are similar and approximate to the oxidizing agent-sulphuric acid systems, previously examined. Based on this analogy a mechanism was proposed for the oxidative homolysis of C-H bonds for the first stage of oxidation of saturated hydrocarbons in anthracene-sulphuric acid and cyclohexene-sulphuric acid systems.

Dc onductivity signals observed following pulsed photoionization of solutions of anthracene in dielectric liquids

dc conductivity in several hydrocarbon liquids containing anthraccne (2 × 10 −6 M) and higher concentrations of efficient electron scavengers is measured following an 18 ns pulse of 248 nm light. With cyclohexane as the solvent, an initial conductivity signal, the origin of which is uncertain, decays over ≈1μs and is initially more than an order of magnitude greater than the much longer lived free-ion signal. Strong effects of the solvent on this initial signal are observed.

Laser system and data analysis techniques for absorbing and non-absorbing excited transients

A comprehensive system for the study of nanosecond kinetics of transient absorbing species is described. It incorporates optical fibre cables facilitating 1.8-180 ns delay between the pump and probe beams. To test the system data were obtained for aerated solutions of anthracene in ethanol and cyclohexane. The build-up of the excited triplet population over approximately 10 ns was observed directly. The possibility of detecting short-lived intermediate states which neither absorb nor fluoresce is discussed.

Two-photon spectroscopy of dipole-forbidden transitions: The low-lying singlet states of anthracene

The two-photon excitation spectrum of anthracene in solution is reported from 29000 to 47000 cm −1. Two-photon al- lowed transitions to 1B 3g(35800 cm −1), 2A g (38000 cm −1) and 3A g (43000 cm −1) are assigned by polarization measure- ments. These results, with those from one-photon spectroscopy, agree with calculations. Theoretical data suggest assignment of a B 3g state to a shoulder at 39000 cm −1 in the two-photon spectrum.

Time-Resolved Reabsorption Effect on the Fluorescence Decay of Anthracene Crystal and Solution

The wavelength dependence of the fluorescence decay time for an anthracene crystal, is discussed with reference to a time dependent reabsorption model, and the time dependence of the reabsorption is shown to be related to the distribution of excitons. From the time-resolved analysis of the temperature dependence of the fluorescence decay, the reabsorption effect is shown to increase over the whole decay period. In order to analyze the concentration dependence of the fluorescence decay in a solution, the Stern-Volmer type equation is applied to the experimental data with two new parameters being introduced. Optimum values of the parameters are obtained from the calculated curves which agree fairly well with the experimental data. The reabsorption effect in the solution increases during a certain time period, but afterwards it decreases.

The photoexcitation of trapped electrons produced in the photoionization of anthracene in liquid n-hexane

The increase in free ions generated by 347 nm light pulses in an n-hexane solution of anthracene by additional excitation at 694 nm is measured at 180–300 K. Combined photoexcitation gives up to 40 times more ions at 185 K. The effect is attributed to an increased probability of electron-ion separation by excitation of elections trapped near positive ions.

Quantitation of Phototoxic Hyperemia and Permeability to Protein: II. Inihibition by Histamine (H1 and H2) Receptor Antagonists in Mouse Skin

Exposure of anthracene treated skin to long-wave ultraviolet radiation (UVA) will produce hyperemia, increased vascular permeability, burning and itching. This photosensitized inflammation was produced in the skin of hairless mice by the topical application of a 0.025% (w/v) solution of anthracene followed by exposure to UVA. The resultant hyperemia was quantified by the increase in 51Cr-erythrocyte content (cpm/wet weight) of skin. After 1000 sec (1.3 x 10(4)J/M2) of UVA, the blood content of the skin had increased nine-fold. Pyrilamine (H1 antagonist), administered orally, did not inhibit the hyperemia in response to anthracene-UVA, whereas cimetidine (H2 antagonist) increased the blood content of the skin. However, a combination of pyrilamine and cimetidine significantly inhibited the hyperemia, indicating that histamine may mediate the anthracene-UVA hyperemia via H1 and H2 receptors on dermal vessels. Since neither antagonist alone blocked the response, the mechanism of histamine action in this response may involve histamine receptors on other dermal components in addition to the blood vessels. In particular, the exacerbation of this photosensitized inflammation by cimetidine lends support to the concept of H2 receptors on mast cells which negatively modulate histamine release.