Quenching of the singlet and triplet state of benzene by halogenated alkanes in the vapor phase

1982 ◽  
Vol 60 (13) ◽  
pp. 1767-1774 ◽  
Author(s):  
H. A. Khwaja ◽  
G. P. Semeluk ◽  
I. Unger
Keyword(s):  
Charge Transfer ◽  
Triplet State ◽  
Vapor Phase ◽  
Linear Dependence ◽  
Rate Constants ◽  
Singlet State ◽  
Quenching Rate ◽  
Order Of Magnitude ◽  
Halogenated Alkanes ◽  
Klein’S Model

The second order rate constants (kq) for the quenching of the singlet state of benzene by several halogenated alkanes (viz. CH2Br2, CCl4, CH3CCl3, CHCl3, CHF3, CH3Cl, CH3F, CH2F2, CH2Cl2, CFCl3, CF2Cl2, CF3Cl, CF4) in the vapor phase have been measured. For CCl4, CHCl3, CH2Cl2, and CH3Cl, which were previously studied by Das Gupta and Phillips, there is satisfactory agreement between the kq values obtained in the separate investigations. The linear dependence of the electron affinity of quencher with the corresponding quenching rate constants supports an exciplex mechanism in accordance with Klein's model. Charge transfer occurs from benzene to halogenated alkane and is greater for the chloro alkanes than for mixed fluoro–chloro alkanes. In the case of the triplet state of benzene, whose behaviour was monitored using the sensitized emission of biacetyl technique, quenching effects were at best one order of magnitude smaller and probably involve more than one bimolecular process.

Fluorescence Quenching of Aminodiphenylamines with Chloromethanes

2002 ◽  
Vol 67 (8) ◽  
pp. 1154-1164 ◽  
Author(s):  
Nachiappan Radha ◽  
Meenakshisundaram Swaminathan
Keyword(s):  
Charge Transfer ◽  
Fluorescence Quenching ◽  
Ground State ◽  
Rate Constants ◽  
Quenching Mechanism ◽  
Quenching Rate ◽  
Charge Transfer Interaction ◽  
Electronically Excited ◽  
A Charge

The fluorescence quenching of 2-aminodiphenylamine (2ADPA), 4-aminodiphenylamine (4ADPA) and 4,4'-diaminodiphenylamine (DADPA) with tetrachloromethane, chloroform and dichloromethane have been studied in hexane, dioxane, acetonitrile and methanol as solvents. The quenching rate constants for the process have also been obtained by measuring the lifetimes of the fluorophores. The quenching was found to be dynamic in all cases. For 2ADPA and 4ADPA, the quenching rate constants of CCl4 and CHCl3 depend on the viscosity, whereas in the case of CH2Cl2, kq depends on polarity. The quenching rate constants for DADPA with CCl4 are viscosity-dependent but the quenching with CHCl3 and CH2Cl2 depends on the polarity of the solvents. From the results, the quenching mechanism is explained by the formation of a non-emissive complex involving a charge-transfer interaction between the electronically excited fluorophores and ground-state chloromethanes.

Quenching of the fluorescence of substituted benzenes by halomethanes

1983 ◽  
Vol 61 (9) ◽  
pp. 1952-1956 ◽  
Author(s):  
H. A. Khwaja ◽  
G. P. Semeluk ◽  
I. Unger
Keyword(s):  
Charge Transfer ◽  
Gas Phase ◽  
Singlet State ◽  
Charge Transfer Complex ◽  
Substituted Benzenes ◽  
Exciplex Formation ◽  
Benzene Toluene ◽  
A Charge ◽  
Klein’S Model ◽  
Protonated Molecules

Rate constants, kq, for the quenching of the singlet state of benzene, toluene, p-xylene, fluorobenzene, trifluoromethyl benzene, p-bis(trifluoromethyl)benzene, and aniline by CCl4, CH3CCl3, CHCl3, and CFCl3, in the gas phase have been determined. In each instance the quenching is via a charge-transfer complex with the aromatic acting as donor. There is a linear dependence between ln kq and IP (ionization potential) of the aromatics which supports Klein's model for exciplex formation. The most effective quencher is CCl4 while the least effective is CFCl3. The most effective donor was aniline while the least effective one was p-bis(trifluoromethyl)benzene. In general, fluorinated aromatics are less effective donors than the corresponding protonated molecules.

scholarly journals The role of peroxide in haem degradation. A study of the oxidation of ferrihaems by hydrogen peroxide

1978 ◽  
Vol 174 (3) ◽  
pp. 901-907 ◽  
Author(s):  
S B Brown ◽  
H Hatzikonstantinou ◽  
D G Herries
Keyword(s):  
Hydrogen Peroxide ◽  
Catalytic Activity ◽  
Linear Dependence ◽  
Rate Constants ◽  
Experimental Error ◽  
Ph Dependence ◽  
Monomeric Species ◽  
Order Of Magnitude ◽  
Computer Based

The oxidation of ferrihaems by H2O2 was studied as a model for haem catabolism. Rates of ferrihaem oxidation were evaluated by using a new computer-based method that measures the loss in catalytic activity of the ferrihaem during oxidation. For protoferrihaem, deuteroferrihaem, coproferrihaem and mesoferrihaem, oxidation proceeded via the monomeric species and no dimer contribution was detectable. The pH-dependence of oxidation was studied in the range 6.5–11. Within experimental error, the data were compatible with an inverse linear dependence on [H+]. This was interpreted in terms of attack by HO2- on monomeric ferrihaem. The specific second-order rate constants for oxidation of monomeric species by HO2- were of the same order of magnitude for all the ferrihaems, and were in the sequence coproferrihaem greater than protoferrihaem greater than mesoferrihaem congruent to deuteroferrihaem. A model is suggested involving formation of a ferrihaem monomerperoxide complex, which may either dissociate with the formation of a peroxidatic intermediate or be involved in an intramolecular oxidation of the ferrihaem. Haem catabolism may occur via the same or a similar intermediate.

The primary process in the photolysis of hexafluoroacetone vapour IV. Identification of singlet quenching addends

1968 ◽  
Vol 306 (1487) ◽  
pp. 537-540 ◽  
Keyword(s):  
Excited State ◽  
Fluorescence Spectrum ◽  
Rate Constants ◽  
High Pressures ◽  
Singlet State ◽  
Fluorescence Yield ◽  
Primary Process ◽  
Quantitative Measurements ◽  
Order Of Magnitude ◽  
Emission Study

High pressures of cis -butene-2 interact with an excited state, postulated to be the singlet, of hexafluoroacetone in such a way as to inhibit the decomposition of the ketone but to yield only small, and perhaps negligible, amounts of isomerization (part III). Studies of the undispersed emission support the hypothesis that the singlet state is involved ; when present at high pressures both isobutene and cis -butene-2 reduce the fluorescence yield to zero. The fluorescence spectrum is decreased in intensity, but essentially unchanged in shape, in the presence of moderate amounts of biacetyl. Quantitative measurements of both these effects were made and values for the rate constants for the quenching of the singlet state were derived. An approximate value of the quenching constant obtained from work on the decomposition in the presence of cis -butene-2 agreed as to order of magnitude with that derived from the emission study.

Quenching of Fluorescence of Chloropentafluoroacetone by Saturated Hydrocarbons

1972 ◽  
Vol 50 (9) ◽  
pp. 1429-1432 ◽  
Author(s):  
A. J. Yarwood
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Singlet State ◽  
Fluorescence Yield ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Quenching Rate ◽  
Saturated Hydrocarbons ◽  
Phase Measurements ◽  
Electronically Excited

Saturated hydrocarbons can quench the electronically excited singlet state of a simple ketone in the gas phase. Measurements on the quenching of the fluorescence yield of chloropentafluoroacetone at 23 °C show that different saturated hydrocarbons can deactivate the excited singlet state with varying efficiencies. The quenching rate constants are reported and possible relationships considered.

Fluorescence Lifetime and Quenching Rates for N,N,N′,N′-Tetramethyl-P-Phenylenediamine in the Vapor Phase

1989 ◽  
Vol 43 (8) ◽  
pp. 1406-1409 ◽  
Author(s):  
S. K. Nickle ◽  
L. A. Melton
Keyword(s):  
Vapor Phase ◽  
Fluorescence Lifetime ◽  
Ground State ◽  
Rate Constants ◽  
Quenching Rate ◽  
Electronically Excited ◽  
Visualization Systems ◽  
Fuel Evaporation ◽  
Vapor Liquid

The fluorescence lifetime of N,N,N′,N′-tetramethyl- p-phenyIenediamine (TMPD) in the vapor phase has been determined to be 3.2 ± 0.3 ns for excitation at 337 nm. The rate constants for quenching of electronically excited TMPD by ground-state TMPD, O2, and CO2 have been determined to be <1 × 10−10 cm3/s, (9.9 ± 1.0) × 10−10 cm3/s, and <4 × 10−13 cm3/s, respectively. The rate for TMPD implies that self-quenching is negligible up to pressures of at least 10 Torr. The quenching rate by oxygen is sufficiently high to ensure that use of TMPD as a quantitative marker for fuel evaporation in exciplex-based vapor/liquid visualization systems is probably not possible if significant quantities of oxygen—as would be the case in combustion environments—are present.

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