Time resolved electronic spectroscopy. I. Bimolecular rates for excimer formation

1969 ◽  
Vol 22 (1) ◽  
pp. 9 ◽  
Author(s):  
R Speed ◽  
r Selinge
Keyword(s):  
Time Delay ◽  
Fluorescence Intensity ◽  
Electronic Spectroscopy ◽  
Flash Duration ◽  
Time Resolved ◽  
Excimer Fluorescence ◽  
Low Viscosity ◽  
Diffusion Controlled ◽  
Excimer Formation ◽  
Bimolecular Quenching

The time delay in the build-up of excimer fluorescence for solutions of pyrene affords a means of testing the assumption that bimolecular quenching of fluorescence is diffusion-controlled. It appears that in solvents of low viscosity this is no longer the case. An apparatus is described with which measurements of fluorescence intensity at nanosecond intervals can be made using a simple versatile high- intensity lamp of short flash duration.

'Excimer’ fluorescence II. Lifetime studies of pyrene solutions

1963 ◽  
Vol 275 (1363) ◽  
pp. 575-588 ◽  
Keyword(s):  
Binding Energy ◽  
Light Source ◽  
The Other ◽  
Collision Process ◽  
Excimer Fluorescence ◽  
Diffusion Controlled ◽  
Excimer Formation ◽  
The Difference ◽  
Lifetime Studies ◽  
Modulated Light

Measurements have been made of the concentration dependence of the rise and decay time characteristics of the monomer and excimer fluorescence of deoxygenated solutions of pyrene in cyclohexane at temperatures from 293 to 340 °K. Two independent methods were employed, one using a pulsed light source and a pulse-sampling oscilloscope, and the other a modulated light source and a phase and modulation fluorometer. In conjunction with observations of the monomer and excimer fluorescence quantum efficiencies, the results have been analyzed to determine the six rate parameters which describe the behaviour of the system. Values of 6.8 x 10 -7 and 0.9 x 10 -7 s are obtained for the radiative lifetimes of the monomer and excimer, respectively. Excimer formation is shown to be a diffusion-controlled collision process, in which every collision between excited and unexcited molecules is effective. From the difference in the activation energies for excimer dissociation and formation, the excimer binding energy is found to be 0.34eV.

scholarly journals Unfolding of Helical Poly(L-Glutamic Acid) in N,N-Dimethylformamide Probed by Pyrene Excimer Fluorescence (PEF)

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1690
Author(s):  
Weize Yuan ◽  
Remi Casier ◽  
Jean Duhamel
Keyword(s):  
Glutamic Acid ◽  
Local Density ◽  
Guanidine Hydrochloride ◽  
Racemic Mixture ◽  
Excimer Fluorescence ◽  
Excimer Formation ◽  
Blob Model ◽  
Α Helix ◽  
The Relationship ◽  
Pyrene Excimer Formation

The denaturation undergone by α–helical poly(L-glutamic acid) (PLGA) in N,N-dimethylformamide upon addition of guanidine hydrochloride (GdHCl) was characterized by comparing the fluorescence of a series of PLGA constructs randomly labeled with the dye pyrene (Py-PLGA) to that of a series of Py-PDLGA samples prepared from a racemic mixture of D,L-glutamic acid. The process of pyrene excimer formation (PEF) was taken advantage of to probe changes in the conformation of α–helical Py-PLGA. Fluorescence Blob Model (FBM) analysis of the fluorescence decays of the Py-PLGA and Py-PDLGA constructs yielded the average number (<Nblob>) of glutamic acids located inside a blob, which represented the volume probed by an excited pyrenyl label. <Nblob> remained constant for randomly coiled Py-PDLGA but decreased from ~20 to ~10 glutamic acids for the Py-PLGA samples as GdHCl was added to the solution. The decrease in <Nblob> reflected the decrease in the local density of PLGA as the α–helix unraveled in solution. The changes in <Nblob> with GdHCl concentration was used to determine the change in Gibbs energy required to denature the PLGA α–helix in DMF. The relationship between <Nblob> and the local density of macromolecules can now be applied to characterize the conformation of macromolecules in solution.

In-Situ, Time Resolved, Kinetics of Reactions in Co-Ge thin Films

1991 ◽  
Vol 237 ◽  
Author(s):  
R. M. Walser ◽  
Byung-Hak Lee ◽  
Alaka Valanju ◽  
Winston Win ◽  
M. F. Becker
Keyword(s):  
Depth Profiling ◽  
Laser Interferometry ◽  
Semiconductor Interface ◽  
Time Resolved ◽  
Interface Reactions ◽  
Valuable Adjunct ◽  
Diffusion Controlled ◽  
Sputter Deposited ◽  
Time Required

ABSTRACTWe report the first kinetic study of metal-semiconductor interface reactions using in-situ, time resolved, laser interferometry. Diffusion couples with Co/Ge thicknesses of 1500 Å/1500 Å were sputter deposited on silicon wafers, and vacuum-annealed at temperatures between 300°C-400°C. Under these conditions polycrystalline CoGe was expected to form [1]. Real time laser (HeNe 6328 Å) interferograms for each anneal were recorded in-situ. These data were supplemented by information from AES and X-ray.For temperatures below 400°C the diffusion controlled formation of CoGe was observed. The composition was confirmed by Auger depth profiling that showed uniform Co and Ge concentrations when the reaction went to completion. The well defined interferences fringes were formed by the dissolution of amorphous Ge. The activation energy = 1.6 eV for the formation of CoGe were determined with precision from the temperature dependence of the time required to anneal the fixed λ/4 distance between adjacent minima and maxima of the interferogram. We discuss the evidence for formation of an intermediate Co-rich compound following the initial diffusion of Co into Ge. The results of these experiments indicate that optical interferometry will be a valuable adjunct to other techniques used to study metal-semiconductor interface reactions.

scholarly journals Time-resolved and temperature tuneable measurements of fluorescent intensity using a smartphone fluorimeter

The Analyst ◽  
2017 ◽  
Vol 142 (11) ◽  
pp. 1953-1961 ◽  
Author(s):  
Md Arafat Hossain ◽  
John Canning ◽  
Zhikang Yu ◽  
Sandra Ast ◽  
Peter J. Rutledge ◽  
...  
Keyword(s):  
Steady State ◽  
Fluorescence Intensity ◽  
Time Resolved Fluorescence ◽  
Time Resolved ◽  
Fluorescent Intensity ◽  
Intensity Measurements

A smartphone fluorimeter is demonstrated for steady-state and time-resolved fluorescence intensity measurements at tunable temperatures.

Spectral properties of ionic derivatives of pyrene and their aggregates with anionic surfactant and polyelectrolyte

1995 ◽  
Vol 73 (11) ◽  
pp. 1948-1954 ◽  
Author(s):  
Pavol Hrdlovič ◽  
Lubica Horinová ◽  
Štefan Chmela
Keyword(s):  
Butyric Acid ◽  
Sodium Salt ◽  
Polyacrylic Acid ◽  
Sodium Dodecylsulfate ◽  
Green Emission ◽  
Water Soluble ◽  
Diffusion Controlled ◽  
Packed Structure ◽  
Bimolecular Quenching ◽  
Derivatives Of

A multifunctional probe based on pyrene, the chloride of the 2,2,6,6-tetramethyl-4-hydroxy-piperidinium ester of 4-(1-pyrene)butyric acid, at a concentration of 5 × 10−5 mol dm−3 exhibits excimer-like green emission with the maximum at 480 nm in the presence of sodium dodecylsulfate below its critical micelle concentration. A similar effect has been observed for this probe in the presence of the sodium salt of polyacrylic acid in the same concentration range. 1-Pyrenemethylammonium chloride exhibits a broad green excimer-like emission for sodium dodecylsulfate but not for the sodium salt of polyacrylic acid. The quenching constants of the monomeric and excimer-like emissions were determined for acrylamide, 1-oxo-2,2,6,6-tetramethyl-4-hydroxypiperidine, potassium iodide, and copper(II) sulfate, representing neutral, ionic, and free-radical types of quenchers. The rate constants of quenching for N-oxyl radicals indicate that the monomeric emission from both water-soluble probes is diffusion controlled. For other types of quenchers the rate constant of bimolecular quenching is lower. The quenching of the excimer-like emission of an aggregate of the chloride of the 2,2,6,6-tetramethyl-4-hydroxypiperidinium ester of 4-(1-pyrene)butyric acid is less efficient than in the case of 1-pyrenemethylammonium chloride, which indicates a more packed structure of the former aggregate. Keywords: pyrene, ionic derivative, emission, micelle, aggregation, quenching.

The Scission of Polysulfide Crosslinks in Scrap Rubber Particles through Phase Transfer Catalysis

1982 ◽  
Vol 55 (5) ◽  
pp. 1499-1515 ◽  
Author(s):  
Paul P. Nicholas
Keyword(s):  
Phase Transfer ◽  
Alkylating Agents ◽  
Decomposition Reaction ◽  
Chain Scission ◽  
Model Studies ◽  
Low Viscosity ◽  
Diffusion Controlled ◽  
Onium Salts ◽  
Rubber Particles ◽  
Rate Behavior

Abstract Hydroxide ions transported by onium ions from water into swollen rubber particles rapidly break polysulfide crosslinks with little or no main chain scission. However, methylated monosulfide crosslinks do not cleave under these conditions. The reaction is not truly catalytic because the quaternary ammonium is decomposed. Model studies with N-methyl-N,N,N-tri-n-alkylammonium chlorides and di-2-cyclohexen-1-yl disulfide show that the decomposition reaction involves a highly selective methylation of the thiolate intermediate. However, catalyst decomposition can be inhibited with added alkylating agents. Alkylating agents also improve catalyst efficiency during devulcanization. The Hofmann reaction is yet another route for catalyst decomposition, but the rate is too slow to be competitive. Several onium salts have been examined in this process. In general, those having several large alkyl substituents are the better performers, consistent with the known partitioning/reaction rate behavior of such catalysts in simple, low viscosity solvents. However, with N-methyl-N,N,N-tri-n-alkylammonium chlorides, the rate decreases as the tri-n-alkyl substituents become very large, e.g., C18H37. This may originate from a slow, diffusion-controlled reaction that is peculiar to the network structure of the swollen vulcanizate.

scholarly journals Pattern Formation in Predator-Prey Model with Delay and Cross Diffusion

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Xinze Lian ◽  
Shuling Yan ◽  
Hailing Wang
Keyword(s):  
Time Delay ◽  
Pattern Formation ◽  
Turing Instability ◽  
Predator Prey ◽  
Cross Diffusion ◽  
Predator Prey Model ◽  
Prey Model ◽  
Diffusion Controlled ◽  
The Stability ◽  
Self Replication

We consider the effect of time delay and cross diffusion on the dynamics of a modified Leslie-Gower predator-prey model incorporating a prey refuge. Based on the stability analysis, we demonstrate that delayed feedback may generate Hopf and Turing instability under some conditions, resulting in spatial patterns. One of the most interesting findings is that the model exhibits complex pattern replication: the model dynamics exhibits a delay and diffusion controlled formation growth not only to spots, stripes, and holes, but also to spiral pattern self-replication. The results indicate that time delay and cross diffusion play important roles in pattern formation.

Instantaneous contribution in time-resolved four-wave mixing from GaAs quantum wells near zero time delay

1994 ◽  
Vol 50 (20) ◽  
pp. 15086-15094 ◽  
Author(s):  
D. S. Kim ◽  
J. Shah ◽  
T. C. Damen ◽  
Wilfred Schäfer ◽  
L. N. Pfeiffer ◽  
...  
Keyword(s):  
Time Delay ◽  
Quantum Wells ◽  
Four Wave Mixing ◽  
Wave Mixing ◽  
Time Resolved ◽  
Zero Time

‘Excimer’ fluorescence I. Solution spectra of 1:2-benzanthracene derivatives

1963 ◽  
Vol 274 (1359) ◽  
pp. 552-564 ◽  
Keyword(s):  
Quantum Yield ◽  
Crystal Lattice ◽  
Excited States ◽  
Concentration Dependence ◽  
Fluorescence Spectra ◽  
Excimer Fluorescence ◽  
Relative Quantum Yield ◽  
Relative Quantum ◽  
Different Types ◽  
Excimer Formation

Observations have been made of the concentration dependence of the fluorescence spectra of solutions of 1:2-benzanthracene and fifteen of its hydrocarbon derivatives. All of the compounds, except the 9,10-dim ethyl derivative, exhibit dim er emission at higher concentrations. The lower excited states, 1 L b and 1 L a , satisfy Förster’s conditions for fluorescent dim er formation. The factors determining the relative quantum yield of excimer fluorescence are discussed. The different types of crystal fluorescence spectra shown by the compounds are explained in terms of excimer formation in the crystal lattice.

Resonance energy transfer study of laser dyes LD 489 and LD 473 with rhodamine 6G

2014 ◽  
Vol 92 (4) ◽  
pp. 302-306 ◽  
Author(s):  
H.R. Deepa ◽  
J. Thipperudrappa ◽  
H.M. Suresh Kumar
Keyword(s):  
Energy Transfer ◽  
Rhodamine 6G ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Laser Dyes ◽  
Rate Parameter ◽  
Quenching Rate ◽  
Range Interaction ◽  
Time Resolved ◽  
Bimolecular Quenching

The energy transfer using two laser dyes 6,7,8,9-tetrahydro-6,8,9-trimethyl-4-(trifluoromethyl)-2H-pyrano[2,3-b][1,8]naphthyridin-2-one (LD-489) and 1,2,3,8-tetrahydro-1,2,3,3,8-pentamethyl-5-(trifluoromethyl)-7H-pyrrolo[3,2-g]quinolin-7-one (LD-473) as donors and rhodamine 6G (Rh6G) as acceptor was investigated in methanol using steady state and time resolved fluorescence spectroscopy. The bimolecular quenching rate parameter, kq, and the translation diffusion rate parameter, kd, were calculated and these values indicated that the diffusion process alone does not operate in energy transfer process. The mean diffusion length, d1, is found to be less than the Förster distance, R0, supporting the dominance of long-range interaction. The critical transfer distances determined from both the Förster equation and the half quenching concentration are close to one another, revealing that the Förster mechanism plays an important role in overall energy transfer of the donors.

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