Excited state carbon acid dissociation and competing photorearrangements of 5H-dibenzo[a,c]cycloheptene derivatives

1996 ◽  
Vol 74 (8) ◽  
pp. 1447-1464 ◽  
Author(s):  
David. Budac. ◽  
Peter Wan
Keyword(s):  
Excited State ◽  
Fluorescence Quenching ◽  
Singlet State ◽  
Acid Dissociation ◽  
Excited Singlet ◽  
Deuterium Incorporation ◽  
Group A ◽  
Carbon Acids ◽  
Work Structure ◽  
Carbon Acid

The first examples of dissociating excited state carbon acids were reported by our group. A necessary structural feature is the 5H-dibenzocycloheptene ring system where the incipient carbanion is formally an antiaromatic system in S0. In this work, structure–reactivity studies of the excited singlet state carbon acid dissociation and competing formal di-π-methane rearrangement of several 5H-dibenzo[a,c]cycloheptene derivatives have been carried out in order to gain more insights into the photochemistry displayed by these compounds. Photolysis of 7-deuterio-5H-dibenzo[a,c]cycloheptene (9) in aqueous solution showed that the photogenerated carbanion is allylically delocalized. Derivative 7 was found to be less reactive than 3 with respect to carbon acid dissociation whereas 8 was unreactive. Ethanolamine (in CH3CN) was found to be an effective base in catalyzing carbon acid dissociation for 3, 7, and 9, as indicated by higher yields of deuterium incorporation and rates of fluorescence quenching. Binaphthyl derivatives 10 and 11 displayed contrasting photobehaviour. Photolysis of binaphthyl 11 resulted in only efficient (ΦP = 0.47) formal di-π-methane rearrangement under all conditions and no evidence was found for carbon acid dissociation, even in the presence of ethanolamine as base. On the other hand, the formal di-π-methane reaction was very inefficient for binaphthyl 10 (Φp < 0.001). Due to the conformational rigidity inherent in 10, the methylene protons at the 3-position are NMR resolvable as pseudo-axial and pseudo-equatorial protons. Photolysis in the presence of ethanolamine (in D2O–CH3CN) resulted in stereoselective deprotonation of the pseudo-axial proton (Φex ≈ 0.02), as indicated by deuterium exchange studies. The results show that excited state carbon acid dissociation is an observable general reaction of dibenzo and dinaphtho cycloheptenes only if more favourable photochemical pathways are not competing. Key words: excited state carbon acid, di-π-methane rearrangement, carbanion, stereoelectronic effect, fluorescence quenching.

Photochemistry of Nitracrine and its Analogues: Acridine Derivatives as Electron Donors

1984 ◽  
Vol 39 (2) ◽  
pp. 195-200 ◽  
Author(s):  
J. Biedrzycki ◽  
J. Błażejowski ◽  
J. Szychliński ◽  
A. Ledòchowski
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Fluorescence Quenching ◽  
Triplet State ◽  
Uv Radiation ◽  
Electron Acceptor ◽  
Singlet State ◽  
Electron Donors ◽  
Excited Singlet State ◽  
Excited Singlet

Studies on the electron transfer in the excited state from electron donors: acridine, 9- aminoacridine and its derivatives, including nitracrine and its isomers, to CCl4 as a suitable electron acceptor, were undertaken. UV radiation (λ= 366 nm), absorbed only by acridine bases, generates CI- ions. The fluorescence quenching measurements indicate that no interaction appears between molecules of acridine bases in the excited singlet state and CCl4 molecule. A scheme of photochemical processes is proposed which assumes that the triplet state of the base molecule is the reactive one.

Photoconductivity studies of perylene tetracarboxyl-diimides

1985 ◽  
Vol 63 (1) ◽  
pp. 134-139 ◽  
Author(s):  
Zoran D. Popovic ◽  
Rafik O. Loutfy ◽  
Ah-Mee Hor
Keyword(s):  
Fluorescence Quenching ◽  
Electric Field ◽  
Visible Light ◽  
Spectral Range ◽  
Singlet State ◽  
Visible Spectral Range ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Carrier Generation

Photoconductivity of a series of perylene tetracarboxyl-dimides has been studied by delayed-collection-field and electric field induced fluorescence quenching techniques. It has been shown that these materials exhibit both extrinsic (impurity controlled) and intrinsic carrier generation originating from the first excited singlet state. Perylene tetracarboxyl-diimides are photoactive in the visible spectral range and their carrier generation efficiencies compare well with generation efficiencies in the best known organic photoconductors. This makes them suitable for xerographic applications using visible light.

Permanent Dipole Moment and Polarizability of a Gass of Merocyanine Dyes in Their Ground and First Excited Singlet State

1983 ◽  
Vol 38 (9) ◽  
pp. 995-1002 ◽  
Author(s):  
Wolfram Baumann
Keyword(s):  
Dipole Moment ◽  
Excited State ◽  
Electric Field ◽  
Field Model ◽  
Singlet State ◽  
Excited Singlet State ◽  
Permanent Dipole Moment ◽  
Excited Singlet ◽  
Reaction Field ◽  
Merocyanine Dyes

Abstract The permanent dipole moment of a class of merocyanine dyes in their ground and first excited singlet state has been determined studying the influence of an external electric field on the absorption of the compounds in various solvents. Evaluation of the experimental results on the basis of the Onsager reaction field model also gives values for the polarizability in the ground and excited state, the latter approaches the value of a respective conducting ellipsoid with the longer chainlength molecules.

Excited State Properties of Peridinin:  Observation of a Solvent Dependence of the Lowest Excited Singlet State Lifetime and Spectral Behavior Unique among Carotenoids

1999 ◽  
Vol 103 (41) ◽  
pp. 8751-8758 ◽  
Author(s):  
James A. Bautista ◽  
Robert E. Connors ◽  
B. Bangar Raju ◽  
Roger G. Hiller ◽  
Frank P. Sharples ◽  
...  
Keyword(s):  
Excited State ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Spectral Behavior ◽  
Solvent Dependence

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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