Fluorescence with benzene

Figure 5.16. Plot of data for the external heavy-atom quenching of pyrene fluorescence in benzene at 20°C. Polaro-graphic half-wave reduction potentials Ein are used as a measure of the electron affinity of the quencher containing chlorine (O), bromine ( ), or iodine (3). From Thomaz and Stevens<148) with permission of W. A. Benjamin, New York.

Carbon disulfide quenches the fluorescence of anthracene quite efficiently,145,149 but seems to have little effect on its triplet lifetime.147 Diphenylanthracene in benzene fluoresces with a quantum yield of 0.8 and shows a high sensitivity to the oxygen concentration in photooxygenation reactions. With about 1 vol% of CS2 present, AC>2 is practically independent of [02] (> 10"5 mole/liter). In jjoth cases, where carbon disulfide was either used as solvent or was added to an otherwise strongly fluorescent solution, the quantum yields of photooxygenation followed... 

In presence of dissolved oxygen, photooxidation may also occur. Bowen and Williams (19) carried out some early experiments with benzene, some of its methyl derivatives, and certain other aromatic hydrocarbons in hexane solutions illuminated with light at 2537 A. They found low values for the quantum yields of fluorescence and of oxygen take-up the sum of these quantities being less than unity. At higher temperatures (>50°C.) chain propagation by a radical mechanism... 

Another example is found with benzene vapor at room temperature. The emission yield (fluorescence only) is about 0.20 0.04 and essentially independent of pressure100,101. There are products formed, although there is some disagreement on this subject and the yields in the gas phase have not been determined. Also there is a crossover from the singlet to the triplet state so that all or nearly all of the primarily excited singlet state molecules either fluoresce or cross over to the triplet state. Nevertheless, in the vapor phase at room temperature, about 80 per cent of the molecules which absorb neither react chemically nor emit radiation100, 101. 

The alkenes, which give emitting exciplexes with benzene, quench its fluorescence at nearly diffusion-controlled rates. For 1,4-dioxene, 2,2-dimethyl-... 

The tissue, plasma, brain or serum was extracted with benzene following basification with a carbonate/bicarbonate buffer at pH 10.5 An ethanol-ized cellulose column was used with a stationary phase of 0.1 M HC1 and a mobile phase cyclohexane 1-pentanol (6 0 followed by extraction into 0.1 M phosphoric acid for fluorescence measurements. 

Benzene is photoreduced by primary, secondary and tertiary amines (Bellas, et al., 1977) and the various products have been identified. The reaction with tertiary amines is accelerated by the addition of small amounts of protic solvents and use of CH3OD leads to deuterium incorporation. These findings are strongly indicative of the participation of radical ions. Primary and secondary amines quench the fluorescence of benzene but whether or not this leads to radical ions is not known. Product studies have been made of the... 

The free acid shows an anomalous Stokes shift only in proton-accepting solvents (acetone, acetonitrile) or mixtures such as toluene/pyridine (36,35), whereas in benzene only normal fluorescence with its maximum near 23,700 cm" is observed. The system 3-hydroxy-2-naphthoic acid in toluene plus small amounts of pyridine has been studied in some detail by Hirota (36) and Ware... 

Sams reported the determination of reserpine in plasma by ion-pair chromatography. To obtain high specifity and to increase the sensitivity reserpine - after extraction from plasma with benzene - was oxidized to 3-dehydroreserpine with vanadium pentoxide in concentrated phosphoric acid, to which 9 ml methanol were added. The fluorescent compound was subsequently analyzed on an octadecyl column with methanol - 0.001 M heptanesulfonate in water (65 35) as mobile phase. Reserpine and rescinnamine could not be distinguished by this method. 

PBO fluoresces with an emission wavelength of -345 nm when osdtcd at 28B nm (Schreiber-Deturmcny eta ., 1993). To determine the structural characteristics responsible for the fluorescence, the fluorescence ot the compounds shown in Table 10.1 was determined. This shows that the fluorescent characteristic is a result of an intact melhylcnedioxy benzene double ring structure. 

Acridone in benzene emits fluorescence with two vibrational peaks at 25200 and 24100 cm". In protic solvents... 

Acridine in benzene emits the fluorescence with three main vibrational bands. The most intense vibronic band is at 24500 cm . The fluorescence band of acridine in ethanol is shifted to the red by 500 cm compared with that in benzene. In an acidic solution, acridine shows a broad emission band which was assigned to the fluorescence of acridinium cation (6). The peak wavenumber of the band is 20700 cm . ... 

The viscosity dependence of emission from the charge-transfer complexes of tetracyanoethylene with benzene and a number of alkylbenzenes has been studied. At high viscosities the fluorescence spectra of alkylbenzenes have a double-band character and the two sub-bands change in different ways with changing viscosity. These observations and the dependence of the excitation spectrum on observation wavelength are discussed in terms of different orientational isomers of the ground-state charge-transfer complexes.1 7... 

Poly(vinyl-1-pyrene). Only exclmer emission Is observed In poly(l-vlnylpyrene) In benzene solution at ambient temperature, and thus the quantum yield of exclmer formation must approach unity. The quantum yield of exclmer fluorescence In benzene solution Is 0.44 (60), and the rate constant kyo was estimated as 8.6 X 10 sec, with kRu equal to 1.0 x lO sec l. 

Microsomal Metabolism of Trp-P-2 Trp-P-2 and AAF were metabolized by the 3-MC rat-liver microsomes in vitro. The extracts with benzene, diethyl ether, ethyl acetate and ethylene chloride were dried before injection onto a reverse-phase yBondapak C-18 column. The HPLC profiles of the metabolites of Trp-P-2 and AAF are very similar(figure 3). These metabolites of Trp-P-2 have the same fluorescence spectra with emission maximum at 332 nm. The UV spectra are identical to that of Trp-P-2, that is, with a maximum at 260 nm. 

We have performed laboratory measurements of rate constants of a few first steps of the tropospheric oxidation mechanism of some monocyclic aromatic hydrocarbons the following reactions have been studied OH radical with benzene or toluene (+M) benzyl radicals (from OH abstraction pathway) with O2, NO and NO2 on the other band, the branching ratios (abstraction/addition + abstraction) have been measured by a direct spectroscopic technique. All these measurements have been achieved thanks to the Discharge Flow (DF) technique with detection of OH by Resonance Fluorescence (RF) and other radicals by Laser Induced Fluorescence (LIF). 

The experimental problems associated with SVL fluorescence are presently severe, and obtaining exciting radiation that is simultaneously tunable, monochromatic, and intense provides the principal challenge. Short-arc xenon arcs coupled with a monochromator have been used with benzene where an exciting bandpass of 15-45 cm has been sufficiently monochromatic to yield SVL fluorescence from a number of states. Narrower bandpasses are needed to extend the list of available levels in the Ba state and to extend this type of experiment to other systems where spectral congestion in absorption is more severe. It is certain that this will be among the important applications of tunable lasers in the near future. 

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