The photochemistry of ring-substituted cinnamyl acetates

2006 ◽  
Vol 84 (9) ◽  
pp. 1146-1154 ◽  
Author(s):  
S A Fleming ◽  
L Renault ◽  
E C Grundy ◽  
J A Pincock
Keyword(s):  
Triplet State ◽  
Singlet State ◽  
Acetoxy Group ◽  
Excited Singlet State ◽  
Excited Triplet State ◽  
Quantum Yields ◽  
Excited Singlet ◽  
Major Pathway ◽  
Excited Triplet ◽  
Fluorescence Quantum Yields

The photochemistry of the (E)-cinnamyl acetates ((E)-1-aryl-3-propenyl acetates, 8a–8e) with substituents H, 4-CH3O, 3-CH3O, 4-CF3, and 3-CF3, respectively, was examined in both cyclohexane and methanol solvents. Alkene isomerization (E to Z) occurred more efficiently than other reactions and evidence is presented that this process occurs from the excited triplet state. In a slower process, 1,3-migration of the acetoxy group led to the rearranged 3-aryl-3-propenyl acetate isomers (9a–9e) as the major pathway, particularly in cylohexane. In methanol, the isomeric ethers 3-aryl-3-methoxypropene (14) and 1-aryl-3-methoxypropene (15) were formed by reaction of methanol with the photochemically generated cation. The combined yield of 14 and 15 (95% and 5%, respectively) was quantitative for the 4-methoxyphenyl compound (8b). Independent irradiations of the isomers 9a–9c demonstrated that the ethers 14 and 15 were primary photoproducts from 8 and not secondary photoproducts from 9. Fluorescence quantum yields and excited singlet state lifetimes indicated that the reactions, other than the E to Z isomerization, are from the excited singlet state.Key words: cinnamyl acetates, photochemistry, E/Z isomerization, photocleavage, fluorescence.

Kinetic model for the molecular system of Zinc(II)-2,9,16,23-phthalocyanine tetracarboxylate

2015 ◽  
Vol 24 (01) ◽  
pp. 1550005 ◽  
Author(s):  
Saleh Al-Omari
Keyword(s):  
Kinetic Model ◽  
Triplet State ◽  
Kinetic Parameters ◽  
Ground State ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Triplet State ◽  
Initial Population ◽  
Excited Singlet ◽  
Excited Triplet

Using vis absorption, fluorescence spectral experimental data, and time-resolved measurement, we have examined the kinetics of Zinc(II)-2,9,16,23-phthalocyanine tetracarboxylate ( ZnPc ( COONa )4), which is interesting photosensitizer of far red-absorption in water: NaOH solution. The kinetic parameters were measured and/or calculated. The photophysical properties originate principally from the planar macrocycle while the outer substituent and degree of carboxylation seem not to have a considerable influence on the kinetic parameters. The nonradiative rate constants of the first excited state were dominant due to the heavy metal effect. Using the obtained photophysical parameters, the population dynamics were calculated by kinetic model. On nanosecond scale of 15 ns, about 63% population of the first excited-singlet state is retrieved by the ground state. Whereas, the rest of population are deactivated to the first excited-triplet state. Later on, during about 7 μs starting from the initial decay of the first excited singlet state, the first excited singlet state and the first excited triplet state were completely empty, meanwhile the ground state retrieved its initial population. Due to the fact that ZnPc ( COONa )4 has strong absorption, long lifetimes of the first singlet and triplet excited states, and fast intersystem crossing, it may be suitable for nonlinear optical studies.

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.

Photolysis of ketene. I

1968 ◽  
Vol 46 (14) ◽  
pp. 2353-2360 ◽  
Author(s):  
A. N. Strachan ◽  
D. E. Thornton
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Triplet State ◽  
Singlet State ◽  
Inert Gases ◽  
Inert Gas ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Increasing Temperature

Ketene has been photolyzed at 3660 and 3130 Å both alone and in the presence of the inert gases C4F8 and SF6. The quantum yield of carbon monoxide has been determined at both wavelengths as a function of pressure and temperature. At 3660 Å the quantum yield decreases with increasing pressure but increases with increasing temperature. At 3130 Å the quantum yield with ketene alone remains 2.0 at both 37 and 100 °C at pressures up to 250 mm. At higher pressures of ketene or with added inert gas the quantum yield decreases with increasing pressure. The results are interpreted in terms of a mechanism in which intersystem crossing from the excited singlet state to the triplet state occurs at both wavelengths, and collisional deactivation of the excited singlet state by ketene is single stage at 3660 Å but multistage at 3130 Å.

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.

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