Intrinsic Quantum Yield Research Articles

Viscosity dependence of the fluorescence lifetimes of cryptocyanine, pinacyanol and DDI

Viscosity dependence of the fluorescence lifetimes of cryptocyanine, pinacyanol and I, I'-diethyl-2,2'-dicarbocyanine iodide (DDI) has been studied by making relative quantum yield measurements in five solvents. It has also been established. by means of flash kinetic spectroscopy, that, in rigid solvents, φ o F+φ o IC ≈ 1 for all three dyes, where φ o F and φ o IC stand for the intrinsic quantum yields of fluorescence emission and internal conversion, respectively. Values of the intrisic rate constant of internal conversion are also presented.

ChemInform Abstract: NONRADIATIVE TRANSITIONS IN THE FIRST EXCITED SINGLET STATE OF PERFLUOROCYCLOBUTANONE, FLUORESCENCE DECAY TIMES AND FLUORESCENCE EXCITATION SPECTROSCOPY

Chemischer InformationsdienstVolume 6, Issue 3 Physical Organic Chemistry ChemInform Abstract: NONRADIATIVE TRANSITIONS IN THE FIRST EXCITED SINGLET STATE OF PERFLUOROCYCLOBUTANONE, FLUORESCENCE DECAY TIMES AND FLUORESCENCE EXCITATION SPECTROSCOPY ROGER S. LEWIS, ROGER S. LEWISSearch for more papers by this authorEDWARD K. C. LEE, EDWARD K. C. LEESearch for more papers by this author ROGER S. LEWIS, ROGER S. LEWISSearch for more papers by this authorEDWARD K. C. LEE, EDWARD K. C. LEESearch for more papers by this author First published: January 21, 1975 https://doi.org/10.1002/chin.197503064AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue3January 21, 1975 RelatedInformation

Nonradiative transitions in the first excited singlet state of perfluorocyclobutanone: Fluorescence decay times and fluorescence excitation spectroscopy

Fluorescence decay times (τF) of an ``isolated'' molecule of perfluorocyclobutanone (PFCB) in its first excited singlet state (S1) with little vibrational energy content and that of a vibrationally relaxed species are 110±4 nsec; the nonradiative lifetime is 112 nsec and the radiative lifetime is 5.4 μsec. These low energy PFCB (S1) species decay chiefly via the S1↝ T1 intersystem crossing route. The value of τF (λex=3577 Å) at ``low pressure'' is 49 nsec, indicating the probable existence of a new electronic relaxation channel below λex=3800 Å. Fluorescence excitation spectroscopy at ``low pressure'' provides the intrinsic fluorescence quantum yield (φF) as a function of exciting wavelength, and it was found that φF begins to decrease below 3800 Å and it is reduced by a factor of 100 below 3480 Å. Collisional lengthening of the τF values at λex=3577 Å indicates that ≤ 1 kcal/mol is lost per collision with a PFCB (S0). From the overlap of the absorption and emission spectra, the 0–0 band of the first singlet n-π* transition is estimated at 4100 Å.

On the nature of the energy-linked quantum yield change in anilinonaphthalene sulphonate fluorescence in submitochondrial particles

It is shown that the energy-linked uncoupler-sensitive increase in the fluorescence of anilinonaphthalene sulphonate probes in submitochondrial particles has two clearly resolvable components: an energy-dependent change in probe binding, and a quantum yield change. The latter is elicited by addition of substrates (succinate or NADH) to coupled submitochondrial particles and is reversed by the addition of uncouplers. Addition of electron transport inhibitors to energized particles results in a decrease in the amount of probe bound but not in the quantum yield, while energization without electron transport enhances binding but not the intrinsic quantum yield of the probe. These observations are explained in terms of two membrane states.

Excimer Fluorescence of Benzene and Its Alkyl Derivatives—Concentration and Temperature Dependence

Fluorescence spectra and quantum yields have been obtained for methylcyclohexane solutions of benzene, toluene, ethylbenzene, cumene, p-, m-, o-xylene, and 1,3,5-, 1,2,3-, 1,2,4-trimethylbenzene as a function of aromatic concentration over the temperature range from 25 to −100°C. At low temperatures distinct excimer emissions were observed for all compounds studied. The intrinsic emission quantum yields of monomer φm and of excimer φe have been determined by a simple technique which requires no assumptions regarding the details of the monomer–excimer kinetics. With decreasing temperature, φe is observed to decrease contrary to the behavior of φm, suggesting that the rate constant for the excimer radiative transition decreases strongly as the temperature is lowered. Such temperature dependence is explained as arising from the existence of a substantial vibronic component in the transition moment that is induced by thermal excitation of upper-state vibrational motions (e.g., torsional, tilting, etc.) of one monomer with respect to the other. From analysis of the temperature dependence of the fluorescence, lower bounds on the excimer binding energies Eb have been determined. The difference between this lower bound and Eb is approximately equal to the activation energy for radiative decay of the excimer. An estimate of this activation energy indicates that, for the case of benzene, Eb > 0.36 eV. The probability for association of excited monomer to form excimer and the probability for dissociation of excimer to an excited and unexcited monomer have been determined for benzene at 25 and −78°C from an appropriate analysis of the fluorescence quenching effect of CCl4. Additionally it has been demonstrated that the observed increase in CCl4 quenching efficiency at high benzene concentrations is predominantly due to an energy migration process. The probability per encounter for formation of excimer has been determined for benzene to be ≈1.0 and to decrease with alkyl substitution in a manner consistent with the steric requirements of sandwich-type excimer configurations.

Kinetics and Mechanism of the Photochemical Valence Tautomerization of Hexafluorobenzene

The kinetics of the photoisomerization of hexafluorobenzene to its ``Dewar'' isomer has been investigated in the gas phase at 2652, 2482, 2288, and 2120 Å. The addition of gases capable of removing vibrational excitation enhances the quantum yield of isomerization indicating that the vibrationally ``hot'' isomer is formed in a rapid reaction. The intrinsic quantum yields of the isomerization process, obtained by extrapolating the observed yields to infinite pressure, are 0.0207±0.0013, 0.0463±0.0031, and 0.081±0.014 at 2652, 2482, and 2288 Å, respectively. These results are in qualitative agreement with predictions of the correlation between the symmetry of the excited state and the direction of photochemical isomerization.