Fluorescence différée et émissions photostimulées du carbazole et de la diphénylamine dans une matrice rigide d'éther à 77 °K

1974 ◽  
Vol 52 (22) ◽  
pp. 3707-3715 ◽  
Author(s):  
D. Muller ◽  
M. Ewald ◽  
G. Durocher
Keyword(s):  
Singlet State ◽  
Delayed Fluorescence ◽  
Quantum Yields ◽  
Constant Ratio ◽  
Light Stimulation ◽  
Excited Singlet ◽  
A Value ◽  
Rate Constant Ratio ◽  
Experimental Values ◽  
Triplet Quantum Yields

The isothermal delayed fluorescence along with the visible (6000 Å) photostimulated fluorescence and phosphorescence emissions have been recorded and analyzed in the following systems: diphénylamine (DPA) – ether rigid glass and carbazole (C) – ether rigid glass at 77°K. The electron–cation recombination after visible light stimulation has been analyzed in terms of a kinetic model already described (10). The triplet quantum yields of the DPA and C molecules are calculated and compared to the existing experimental values. The rate constant ratio (β) of populating the first triplet (T1) relative to populating the first excited singlet (S1) after the recombination event has taken place, is equal to about 2 in both systems investigated here. A value of 4.4 was obtained for indole and tryptophan in the same matrix. This difference can only be explained in terms of various singlet state energies for these molecules and also in terms of the stimulating energies used in these experiments.

Isothermal and Photostimulated Emissions of Indole and Tryptophan in Two Polar Matrices at 77 °K

1974 ◽  
Vol 52 (3) ◽  
pp. 407-417 ◽  
Author(s):  
D. Muller ◽  
M. Ewald ◽  
G. Durocher
Keyword(s):  
Kinetic Model ◽  
Ethylene Glycol ◽  
Singlet State ◽  
Delayed Fluorescence ◽  
Glassy Matrix ◽  
Spin Multiplicity ◽  
Light Stimulation ◽  
Excited Singlet ◽  
Recombination Processes ◽  
Fluorescence And Phosphorescence

The isothermal delayed fluorescence along with the visible photostimulated fluorescence and phosphorescence emissions have been recorded and studied for the following systems: a 10−3 M solution of indole in an ether glassy matrix, a 10−3 M solution of indole in an ethylene glycol–water glassy matrix (EG–W) (70–30 by volume), a 10−3M solution of tryptophan in an EG–W glassy matrix (70–30 by volume). All these experiments have been performed at the temperature of liquid nitrogen. It has also become possible to record the action spectra of the photostimulated emissions which give us information about the entities playing an active part in the recombination processes. The electron–cation recombination after visible light stimulation has been analyzed in terms of a kinetic model based on the assumption that upon neutralization an intermediate state is formed from which the molecule decides what its spin multiplicity will be. It was found that in an EG–W glass at 77 °K about 80% of the recombination events lack the energy necessary to reach the first excited singlet state of the amines studied. In an ether glass this percentage decreases to about 28%. This result is qualitatively in accord with the fact that the photostimulated electrons are more stabilized in an EG–W glass by an amount of energy equal to 1.5 eV.

Fluoreszenz -Untersuchungen an Distyrylbenzolen

1988 ◽  
Vol 43 (6) ◽  
pp. 583-590 ◽  
Author(s):  
Dieter Oelkrug ◽  
Klaus Rempfer ◽  
Ellen Prass ◽  
Herbert Meier
Keyword(s):  
Singlet State ◽  
Fluorescence Decay ◽  
Excited Singlet State ◽  
Quantum Yields ◽  
Excited Singlet ◽  
Fluorescence Quantum Yields ◽  
Forbidden Transition ◽  
Decay Times ◽  
Fluorescence Decay Times

Abstract The absorption and fluorescence of three isomeric distyrylbenzenes are investigated as function of temperature. From the fluorescence decay times and fluorescence quantum yields two classes of oligostyrylarenes can be distinguished. A decisive criterion for this classification is, whether the first excited singlet state S1 belongs to an allowed or forbidden transition S0→S1.

Photovoltaic Effect of Acriflavine in Collodion Film

1969 ◽  
Vol 24 (5) ◽  
pp. 520-523 ◽  
Author(s):  
Giiti Tomita
Keyword(s):  
Thin Film ◽  
Singlet State ◽  
Photovoltaic Effect ◽  
Delayed Fluorescence ◽  
Positive Sign ◽  
Excited Singlet ◽  
Photovoltaic Effects ◽  
Reduction And Oxidation ◽  
Collodion Film ◽  
Dye Molecule

The photovoltaic effects of free and bound acriflavine were studied to find the elemenatary processes in photochemical behaviours of the dye. The observed photopotential in aqueous acriflavine solution is positive or negative against the dark electrode, depending on pH. The positive sign implys that the photoreduction of dye is more predominant than the photooxidation. The negative sign is obtained when the photooxidation is the predominant reaction.Using the electrode coated directly or indirectly with a very thin film of acriflavine-dispersed collodion, the contributions from photo-reduction and -oxidation to the photopotential were separated. The spectral sensitivity of photopotentials gives us an useful information about the oxidationreduction mechanism of bound dyes. The photo-ejection of an electron from the excited singlet state of dye molecule, which was considered by LIM and others1 to be responsible for the delayed fluorescence of acriflavine in rigid media, seems to be favourable for understanding of photopotential properties at shorter wavelengths of excitation.

The primary process in the photolysis of hexafluoroacetone vapour III. The efficiency of intersystem crossing

1968 ◽  
Vol 306 (1487) ◽  
pp. 529-536 ◽  
Keyword(s):  
Quantum Yield ◽  
Lower Limit ◽  
Singlet State ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Primary Process ◽  
Excited Singlet ◽  
A Value ◽  
Low Concentrations

The value of k 6 /( k 4 + k 5 + k 6 ) (mechanism of part I) was determined by two techniques, namely the sensitization of the isomerization of cis - to trans -butene-2 and the sensitization of the phosphorescence of biacetyl. Both techniques yielded a value for the ratio of 0⋅9 ± 0⋅1. The value obtained by the isomerization technique is a lower limit because the quantum yield for the isomerization did not attain a value independent of [ cis -butene-2], but reached a maximum at low concentrations of olefine and then decreased. A similar scavenging of the excited singlet state of hexafluoroacetone was observed when biacetyl was present as an addend. However, in both cases the measurements were made with sufficiently low concentrations of addend that the singlet scavenging should have introduced less, than 10% error. It is concluded that reaction (5) of the mechanism cannot be an important mode of disappearance of excited ketone molecules.

Substituenteneffekte im spektroskopischen Verhalten von Maleinsäurederivaten und 4-Cyclopenten-1.3-dionen / Substituent Effects on the Spectroscopic Behavior of Maleic Acid Derivatives and 4-Cyclopentene-1,3-diones

1973 ◽  
Vol 28 (9-10) ◽  
pp. 662-681 ◽  
Author(s):  
Hans-Dieter Scharf ◽  
Hans Leismann
Keyword(s):  
Excited States ◽  
Maleic Acid ◽  
Singlet State ◽  
Substituent Effects ◽  
Quantum Yields ◽  
Mo Calculations ◽  
Excited Singlet ◽  
Inductive Effects ◽  
Phosphorescence Emission ◽  
Spectroscopic Behavior

The lowest excited states of maleic acid- and cyclopentendionderivatives have been investigated by UV-absorption and phosphorescence emission spectroscopy. While the first excited singlet-state S1 is of 1(nπ*)-type in all compounds, the lowest triplet-state T1 was found to be a mixture of 3(nπ*) and 3(ππ*)-configurations. For the emitting derivatives (Ζ ≠ Η) phosphorescence-lifetimes and -quantum yields as well as the probability for intersystem crossing have been determined.Considering the inductive effects of all substituents on the S1 (nπ*) -energy, Coulombpotentials for sulfur and iodine in terms of Huckel-parameters: hs = 0,2 and hj = —0,5 have been derived.The results of Hückel-MO-calculations can be correlated to the measured values of all compounds with the exception of the iodine containing derivatives.

Merostabilization in radical ions, triplets, and biradicals. 6. The excited state behaviour of para-substituted tetraphenylethylenes

1981 ◽  
Vol 59 (21) ◽  
pp. 3061-3075 ◽  
Author(s):  
William J. Leigh ◽  
Donald R. Arnold
Keyword(s):  
Cyclic Voltammetry ◽  
Singlet State ◽  
Quantum Yields ◽  
Qualitative Investigation ◽  
Radical Ions ◽  
Excited Singlet ◽  
Triplet Energy ◽  
Reduction Potentials ◽  
Half Wave ◽  
State Behaviour

The half-wave oxidation and reduction potentials, measured by cyclic voltammetry, of tetraphenylethylene and a series of para-substituted (cyano, methyl, and methoxy) derivatives are found to correlate with σ+ and σ− values respectively. The deviations from these correlations that are observed for one of the derivatives (unsymmetrically substituted) are attributed to merostabilization.The nature of the first excited singlet state of these compounds is investigated by spectroscopic and photochemical means. Quantum yields for the direct cis–trans photoisomerization demonstrate that this provides the dominant pathway for decay of the singlet state. The π,π* triplet energies are estimated from a qualitative investigation of the relative efficiencies of triplet-sensitized cis–trans isomerization as a function of sensitizer triplet energy.

Fluorescence of Trans-4-Cyano-4′-dimethylaminostilbene; No Evidence for a TICT State

1983 ◽  
Vol 38 (8) ◽  
pp. 928-936 ◽  
Author(s):  
Henry Gruen ◽  
Helmut Görner
Keyword(s):  
Charge Transfer ◽  
Double Bond ◽  
Relaxation Process ◽  
Singlet State ◽  
Intramolecular Charge Transfer ◽  
Solvent Polarity ◽  
Quantum Yields ◽  
Excited Singlet ◽  
Dual Emission ◽  
Fluorescence Maximum

AbstractThe fluorescence properties of trans-4-cyano-4′-dimethylaminostilbene (trans-1) and a rigid analogue, in which the dimethylaminophenyl group is replaced by an indoline ring, trans-l-(4-cyanophenyl)-2-(5-[2,3-dihydro]N-methylindolyl)ethylene (trans-2) were studied in 20 solvents. The quantum yields of fluorescence (Φf) and of trans→cis photoisomerization (Φt→c) as well as the fluorescence maximum (ν̃f) and the bandwidth (⊿ν̃f) were examined. The activation energies (range: 3.5-7.8 kcal/mol) obtained from <2>f and <£t_c measurements are nearly the same for 1 and 2 in a given solvent. Φf , ν̃f and ⊿ν̃f as a function of solvent polarity and temperature show similar trends for 1 and 2. No dual emission was observed for either of the cyanostilbenes. These findings indicate that a twisted intramolecular charge transfer (TICT) state is not involved in the relaxation process of the first excited trans singlet state (1t*). The main deactivation pathway of 1t* competing with fluorescence is trans→cis photoisomerization by twisting about the C = C double bond in the first excited singlet state for both.

The structure, photochemical reactivity, and photophysical properties of adamantyl X-substituted aryl ethers and a comparison with the alkyl groups, methyl, tert-butyl, and allyl

2005 ◽  
Vol 83 (9) ◽  
pp. 1237-1252 ◽  
Author(s):  
A L Pincock ◽  
J A Pincock
Keyword(s):  
Excited State ◽  
Rate Constants ◽  
Singlet State ◽  
Bond Cleavage ◽  
Photophysical Properties ◽  
Excited Singlet State ◽  
Quantum Yields ◽  
Aryl Ether ◽  
Excited Singlet ◽  
Aryl Ethers

The structure, photophysical properties, and photochemistry of the adamantyl aryl ethers 1 in both methanol and cyclohexane have been examined. UV absorption spectra, 13C NMR chemical shifts, X-ray structures, and Gaussian calculations (B3LYP/6-31G(d)) indicate that these ethers adopt a 90° conformer in the ground state. In contrast, fluorescence spectra, excited singlet state lifetimes, and calculations (TDDFT) indicated a 0° conformer is preferred in the first excited singlet state S1. Irradiation in either solvent results in the formation of adamantane and the corresponding phenol as the major products, both derived from radical intermediates generated by homolytic cleavage of the ether bond. The 4-cyano substituted ether 1j was the only one to form the ion-derived product, 1-methoxyadamantane (16% yield), on irradiation in methanol. Rate constants of bond cleavage for these ethers from S1 were estimated by two different methods by comparison with the unreactive anisoles 2, but the effect of substituents was too small to determine structure–reactivity correlations. The temperature dependence of the quantum yields of the fluorescence of the unsub stituted, 4-methoxy and 4-cyano derivatives of 1 and 2 were also determined. These results indicated that the activated process for 1 was mainly bond cleavage for the 4-cyano substrate whereas for 2, it was internal conversion and intersystem crossing. Key words: aryl ether photochemistry, fluorescence, excited-state rate constants, excited-state temperature effects.

Activation energy barrier for intersystem crossing in platinum phthalocyanine

1976 ◽  
Vol 54 (6) ◽  
pp. 633-637 ◽  
Author(s):  
Tzer-Hsiang Huang ◽  
Klaus E. Rieckhoff ◽  
Eva-Maria Voigt
Keyword(s):  
Triplet State ◽  
Ground State ◽  
Energy Barrier ◽  
Singlet State ◽  
Quantum Yields ◽  
Intersystem Crossing ◽  
Singlet Ground State ◽  
Activation Energy Barrier ◽  
Excited Singlet ◽  
Platinum Phthalocyanine

Phosphorescence quantum yields and lifetimes of platinum phthalocyanine in α-chloronaphthalene solution are reported for temperatures from 1.3 K to 300 K. Activation energies of intersystem crossing are deduced and found to be Ea = 17 ± 3 cm−1 for crossing from the first excited singlet state to the lowest lying triplet state and Eap = 8 ± 1 cm−1 for crossing from the lowest lying triplet state to the singlet ground state.

Sign in / Sign up

Export Citation Format

Share Document