ChemInform Abstract: Photochemistry of Arylmethyl Esters in Nucleophilic Solvents: Radical Pair and Ion Pair Intermediates

ChemInform ◽  
2010 ◽  
Vol 28 (19) ◽  
pp. no-no
Author(s):  
J. A. PINCOCK
Keyword(s):  
Radical Pair ◽  
Ion Pair

Photochemistry of rhodamine dye salts involving intra-ion-pair electron transfer

2003 ◽  
Vol 81 (6) ◽  
pp. 789-798 ◽  
Author(s):  
Guilford Jones II ◽  
Xiaochun Wang ◽  
Jingqiu Hu
Keyword(s):  
Electron Transfer ◽  
Ethyl Acetate ◽  
Rhodamine 6G ◽  
Radical Pair ◽  
Ion Pairs ◽  
Ion Pair ◽  
Thiocyanate Ion ◽  
Rhodamine Dye ◽  
Triplet Radical Pair ◽  
Pair State

The electron-transfer photochemistry of rhodamine 6G thiocyanate ion pairs has been investigated. For dye in a low polarity solvent, such as ethyl acetate, the emission of rhodamine 6G is significantly quenched by thiocyanate counterions. Laser photolysis of rhodamine 6G and thiocyanate in ethyl acetate was studied in detail with the identification of the reduced rhodamine 6G radical species (λmax = 410 nm). The growth and decay of the R6G radical could be accounted for in part by a mechanism involving initial formation of dye triplet followed by electron transfer which provides a triplet radical-pair state on a µs timescale.Key words: electron transfer, ion pair, rhodamine 6G, triplet state.

Time-resolved ESR study on photochemical formation of radical pair in cyclodextrin cavities

1991 ◽  
Vol 69 (11) ◽  
pp. 1643-1648 ◽  
Author(s):  
Hisao Murai ◽  
Yoshinori Yamamoto ◽  
Yasumasa J. I'Haya
Keyword(s):  
Aqueous Solution ◽  
Aqueous Solutions ◽  
Spin Polarization ◽  
Room Temperature ◽  
Radical Pair ◽  
Ion Pair ◽  
Time Resolved ◽  
Excited Triplet ◽  
Photochemical Formation ◽  
Fixed Orientation

The photoreduction of xanthone with diethylaniline in cyclodextrin cavities was studied at 77 K and room temperature by a time-resolved ESR technique. The radical pair observed in β- and γ-cyclodextrins showed inverted spin polarization compared to that of precursor excited triplet xanthone. This result is rationalized by taking account of the fixed orientation of the radical ion pair in the cyclodextrins. Frozen aqueous solutions and dried powder-like samples provided similar results. The spectrum of the radical pair was also detected in an aqueous solution of β-cyclodextrin at room temperature. Key words: cyclodextrins, xanthone, spin polarization, radical ion-pair, time-resolved ESR.

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.

The design of radical clocks to probe the reactivity of the intermediates in arylmethyl ester photochemistry

1997 ◽  
Vol 75 (2) ◽  
pp. 232-247 ◽  
Author(s):  
S.M. Nevill ◽  
J.A. Pincock
Keyword(s):  
Singlet State ◽  
Radical Pair ◽  
Ion Pair ◽  
Excited Singlet ◽  
Homolytic Cleavage ◽  
Radical Pairs ◽  
Photochemical Rearrangement ◽  
Radical Clocks ◽  
Radical Clock ◽  
Oxygen Bond

The photochemistry in methanol of the esters 1–6was examined. These reactions normally proceed through radical pairs that result from homolytic cleavage of the carbon–oxygen bond in the excited singlet state. Each of the esters was designed to probe the intervention and reactivity of the substituted arylmethyl radical by incorporating a potential radical clock at the carbon of the reactive bond. For esters 1–5, the products isolated indicated that the radical clock was not reactive enough to compete with the very rapid alternate processes of the radical pair, namely, electron transfer to form the corresponding ion pair and decarboxylation of the phenylacyloxy radical (k = 4.6 × 109 s−1). Ester 6, which incorporates the extremely rapid fluorenylcyclopropylcarbinyl clock, showed very unusual reactivity. On thermal solvolysis in methanol, 6 rearranged quantitatively to the ester 20. No methyl ethers were detected. In contrast, photolysis of 6 in benzene resulted in an alternate rearrangement to the cyclobutyl ester, 22, resulting from the aryl version of the cyclopropyl-π-methane photochemical rearrangement. No ester cleavage occurred on excitation. A rationale for the latter conversion was based on stereoelectronic arguments provided by a crystal structure of 6. Keywords: photochemistry of arylmethyl esters, radical clocks.

Internal return in the photochemistry of ring-substituted 1-(1-naphthyl)ethyl esters of phenylacetic acid

1995 ◽  
Vol 73 (6) ◽  
pp. 885-895 ◽  
Author(s):  
J.M. Kim ◽  
J.A. Pincock
Keyword(s):  
Electron Transfer ◽  
Transfer Rate ◽  
Experimental Error ◽  
Phenylacetic Acid ◽  
Radical Pair ◽  
Ion Pair ◽  
Ethyl Esters ◽  
Electron Transfer Rate ◽  
Radical Pairs ◽  
Substituted 1

The photochemistry in methanol of the esters 12a–d has been studied in order to determine the importance of internal return of both ion pair and radical pair intermediates. The efficiency of internal return, determined by monitoring 18O exchange between the alcohol and carbonyl oxygens, was shown to be substituent dependent, varying from approximately 10% for the 4,7-dimethoxy substrate to nearly 50% for the 4-cyano case. The corresponding ground state solvolysis reactions gave about 10% internal return and, within experimental error, were substituent independent. Internal return was also examined by racemization of the chiral center in 12a and 12d. In summary, these combined results reveal that internal return probably occurs mainly through a contact (not solvent-separated) radical pair. More important, internal return has little effect on previously calculated electron transfer rate constants for converting the radical pair to the ion pair. Therefore, the previously reported Marcus' correlations are valid. Keywords: photochemistry of benzylic esters, internal return, photosolvolysis, electron transfer, radical pairs.

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