scholarly journals Picosecond Absorption Spectroscopy of Polymethine Cis-Trans Isomerization

1988 ◽  
Vol 8 (1) ◽  
pp. 39-47 ◽  
Author(s):  
K.-H. Feller ◽  
R. Gadonas ◽  
V. Krasauskas
Keyword(s):  
Quantum Yield ◽  
Absorption Spectra ◽  
Time Resolved Fluorescence ◽  
Absorption Region ◽  
Time Resolved ◽  
Fluorescence Kinetics ◽  
Double Exponential ◽  
A Minor ◽  
Cis Isomer ◽  
Polymethine Dye

Results are presented of time resolved fluorescence and absorption investigations of DDEOCI (3,3'-diethyl-6,6'-diphenyl-9-ethyl-oxacarbocyanine iodide) in solvents which differ in polarity and viscosity. The measured picosecond absorption and fluorescence kinetics probed at various wavelengths of the polymethine dye studied can be fitted to a double exponential decay with a minor fast component of lifetime τ1 and a major slower component of lifetime τ2. Furthermore, probing in the S1←S0 absorption region and in the fluorescence region results in a residual with a lifetime of some ns and belonging to the detected red-shifted photoisomer with a low quantum yield (φ < 10%). The lifetime and the preexponential factors of the two components are in methanolic solution uneffected by changes of the anion.The detected two picosecond lifetime components are supposed to belong to two isomeric species (all-trans and mono-cis isomer) with strongly overlapping absorption spectra.

Excited state acid catalysis of the 2 + 2 photocycloaddition of methyl 2-naphthoate and acetylacetone; the interaction of a nonfluorescent exciplex with H2SO4

1994 ◽  
Vol 72 (9) ◽  
pp. 2011-2020 ◽  
Author(s):  
Yuan L. Chow ◽  
Carl I. Johansson
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Fluorescence Quenching ◽  
Analytical Method ◽  
Acid Catalysis ◽  
Time Resolved Fluorescence ◽  
Time Resolved ◽  
Fluorescence Kinetics ◽  
Quenching Analysis ◽  
Potential Acid

In this paper, the striking acid catalysis of the photocycloaddition of methyl 2-naphthoate (2MN) to acetylacetone (AA) to give 1 and 2 was traced to the enhanced conversion of the nonemissive *(2MN–AA) exciplex to 1 and 2 by H2SO4. The partial reversibility of the exciplex in CH3CN and CH3OH was established by extended fluorescence-quenching analysis using oxygen to perturb the system, whereas time-resolved fluorescence kinetics failed to reveal the presence of this exciplex. A similar analytical method demonstrated the interaction of the nonfluorescent *(2MN–AA) exciplex and H2SO4 with the rate constants of kap = (2 ± 1) × 109 M−1 s−1 in CH3CN and (4 ± 1) × 109 M−1 s−1 in CH3OH. The quantum yield of photocycloadducts was significantly enhanced at high 2MN conversions owing to the retardation of the competing excimer *(2MN)2 formation. In the range of low conversion (< 15%) and [H2SO4] ≤ 1 mM, the quantum yield was shown to be proportional to H2SO4 concentration; the slope from such plots was analyzed to give kap values similar to those obtained from the extended fluorescence-quenching analysis. This agreement, along with the elimination of other potential acid catalytic routes, unambiguously proves that the acid catalysis originates from the interaction of the *(2MN–AA) exciplex with H2SO4.

Substituted Phosphorous Triazatetrabenzocorroles: Correlation Between Structure and Excited State Properties

2009 ◽  
Vol 62 (5) ◽  
pp. 434 ◽  
Author(s):  
Xian-Fu Zhang ◽  
Yakuan Chang ◽  
Yanling Peng ◽  
Fushi Zhang
Keyword(s):  
Quantum Yield ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Photophysical Properties ◽  
Laser Flash ◽  
Time Resolved Fluorescence ◽  
Absorption Properties ◽  
Strong Electron ◽  
Time Resolved ◽  
Triplet Formation

The photophysical properties of five novel phthalocyanine analogues, dihydroxy phosphorus(v) triazatetrabenzocorrole (PTBC) substituted with –NO2, –SO3H, OiPr, and –NH2, respectively, were studied by a combination of absorption, steady-state emission, time-resolved fluorescence, and laser flash photolysis. All substituents, even for the strong electron-donating –NH2, cause only a slight red shift of their absorption and emission maxima. These complexes are generally monomeric in organic solution, whereas the sulfonated derivative, PTBC(SO3H)4, slightly aggregates in aqueous buffer. Distinct from phthalocyanines, PTBCs substituted with –NO2 or –NH2 still show high photo activities. The electron-withdrawing –NO2 and –SO3H decrease the fluorescence quantum yield but increase the triplet formation yield to 0.76 and 0.82, respectively. All PTBCs have long triplet lifetimes and hence generate singlet oxygen efficiently with a quantum yield from 0.43 to 0.75. Together with the ground-state absorption properties, the results suggest that these PTBCs may be used as excellent photosensitizers for photodynamic therapy.

Porphyrin−Dendrimer Assemblies Studied by Electronic Absorption Spectra and Time-Resolved Fluorescence

2003 ◽  
Vol 36 (24) ◽  
pp. 9135-9144 ◽  
Author(s):  
Pedro M. R. Paulo ◽  
Roel Gronheid ◽  
Frans C. De Schryver ◽  
Sílvia M. B. Costa
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Time Resolved Fluorescence ◽  
Time Resolved

Time-resolved fluorescence and proton NMR studies of tyrosine and tyrosine analogs: correlation of NMR-determined rotamer populations and fluorescence kinetics

Biochemistry ◽  
1986 ◽  
Vol 25 (3) ◽  
pp. 599-607 ◽  
Author(s):  
William R. Laws ◽  
J. B. Alexander Ross ◽  
Herman R. Wyssbrod ◽  
Joseph M. Beechem ◽  
Ludwig Brand ◽  
...  
Keyword(s):  
Proton Nmr ◽  
Time Resolved Fluorescence ◽  
Nmr Studies ◽  
Time Resolved ◽  
Fluorescence Kinetics
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