Intramolecular electron transfer in the photochemistry of substituted 1-naphthylmethyl esters of benzoic acids

1992 ◽  
Vol 70 (7) ◽  
pp. 1879-1885 ◽  
Author(s):  
D. P. DeCosta ◽  
J. A. Pincock
Keyword(s):  
Electron Transfer ◽  
Singlet State ◽  
Bond Cleavage ◽  
Ion Pair ◽  
Excited Singlet State ◽  
Intramolecular Electron Transfer ◽  
Excited Singlet ◽  
Transfer Rates ◽  
Exciplex Formation ◽  
Direct Excitation

Direct excitation of the esters 5 in methanol solvent leads to rapid intramolecular exciplex formation (kex = 1010 s−1 for X = CH3O, Y = CN) with electron transfer from the naphthalene to the benzoate ring. This process dominates the usual fluorescence and reaction of the excited singlet state. The rate of this process can be varied over 103 by suitable change in the substituents X and Y. The electron-transfer rates can be correlated with the two-parameter Hammett equation: log kex = 8.48 − 1.5σ+ + 0.77σ. For cases where the rate of exciplex formation is slow, the usual homolytic carbon–oxygen bond cleavage occurs from the excited singlet state. The eventual products result from the ion pair since the rate of electron transfer in the radical pair to form the ion pair is considerably faster than the rate of decarboxylation of the benzoyloxy radical.

scholarly journals The photochemistry of 1-naphthylmethyl carbonates and carbamates

1994 ◽  
Vol 72 (5) ◽  
pp. 1254-1261 ◽  
Author(s):  
T. Parman ◽  
J.A. Pincock ◽  
P.J. Wedge
Keyword(s):  
Electron Transfer ◽  
Singlet State ◽  
Radical Pair ◽  
Ion Pair ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Homolytic Cleavage ◽  
Product Yields ◽  
Oxygen Bond

The photochemistry in methanol of 1-naphthylmethyl phenyl carbonate (3) and 1-naphthylmethyl benzyl carbonate (4) has been studied. Products resulting from both the 1-naphthylmethyl cation and the 1-naphthylmethyl radical are obtained for 3, but only from the cation for 4. Similar results were obtained for the corresponding 1-naphthylmethyl derivatives 5 and 6 of N-phenyl and N-benzyl carbamic acids. The product yields for all four compounds can be explained by a mechanism of initial homolytic cleavage of the 1-naphthylmethyl carbon–oxygen bond from the excited singlet state. The radical pair generated then partitions between the two pathways: electron transfer to form the ion pair or decarboxylation. For PhO-CO-O• and PhNH-CO-O•, decarboxylation is rapid and competitive with electron transfer. For PhCH2O-CO-O• and PhCH2NH-CO-O•, decarboxylation is slower, electron transfer dominates, and only products from the ion pair are obtained.

Spin-Polarized Radical Ion Pair Formation Resulting from Two-step Electron Transfer from the Lowest Excited Singlet State of a Fixed-Distance Photosynthetic Model System at 5 K

1991 ◽  
Vol 194 (1) ◽  
pp. 201-207 ◽  
Author(s):  
Michael R. Wasielewski ◽  
George L. Gaines ◽  
Michael P. O'neil ◽  
Walter A. Svec ◽  
Mark P. Niemczyk
Keyword(s):  
Electron Transfer ◽  
Singlet State ◽  
Model System ◽  
Ion Pair ◽  
Pair Formation ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Ion Pair Formation ◽  
Fixed Distance ◽  
Spin Polarized

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.

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.

Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyloxy radicals

1992 ◽  
Vol 70 (3) ◽  
pp. 992-999 ◽  
Author(s):  
James W. Hilborn ◽  
James A. Pincock
Keyword(s):  
Electron Transfer ◽  
Singlet State ◽  
Intramolecular Charge Transfer ◽  
Radical Pair ◽  
Product Distribution ◽  
Intramolecular Electron Transfer ◽  
Naphthalene Ring ◽  
Excited Singlet ◽  
Homolytic Cleavage ◽  
Oxygen Bond

The photolysis of esters 6 and 8 in methanol leads to products resulting from both naphthylmethyl cations and radicals. The product distribution is nearly independent of X for the esters 6 except when X equals methoxy. A mechanism involving initial homolytic cleavage of the carbon–oxygen bond in the excited singlet state of the ester is proposed. Competition between electron transfer in the radical pair to form the ion pair and decarboxylation of the arylacyloxy radical allows calculations of the rates for this decarboxylation process. The ρ value versus σ is close to zero. When X equals methoxy, intramolecular electron transfer occurs with the naphthalene ring serving as the acceptor and the methoxyaromatic as the donor. This exciplex fragments to carbon dioxide and 1-(1-naphthyl)-2-arylethane. Keywords: acyloxy radical, decarboxylation, photolysis of benzylic esters.

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