Photosensitization of quadricyclene isomerization by electron acceptors. A short-circuit nonradiative decay mechanism for electron donor-acceptor quenching in polar media

Jones, Guilford; Chiang, Sheau-Hwa; Becker, William G.; Welch, Jeanne A.

doi:10.1021/j100212a001

Cited by 31 publications

(12 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…are very reactive, the net quantum yields for the monomerization can not reach unity as the consequence of rapid geminate recombination of IRP. Such rapid geminate recombination of IRP predominating over the dissociation has been frequently observed in electrontransfer reactions of strained molecules (Jones et al, 1982;Davis et al, 1984;Kumar et al, 1984;Pac et al, 1987). In those cases, substantial molecular distortions of the strained compounds might occur after electron transfer to open up a particular channel for the rapid geminate recombination of IRP Figure 4.…”

Section: Resultsmentioning

confidence: 92%

CHLORANIL‐PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMERS and EFFECT OF MAGNESIUM PERCHLORATE

Pac

Miyamoto

Masaki

et al. 1990

Photochem & Photobiology

View full text Add to dashboard Cite

The photosensitized monomerization of the cyclobutane dimers of 1,3-dimethylthymine by p-chloranil was investigated by means of steady-state irradiation and laser-flash photolysis. Quantum yields for the monomerization are 0.34 for the cis,syn dimer, 0.39 for the trans,syn dimer, and much less than 10(-2) for the cis,anti isomer. Formation of the chloranil anion radical associated with quenching of triplet chloranil by the dimers demonstrates that electron transfer from dimers to triplet chloranil occurs to initiate the monomerization. Kinetic analysis suggested that the syn-dimer cation radicals undergo the ring cleavage at greater than or equal to 10(9) s-1 before escaping from the solvent cage, while the reactivity of the anti-dimer cation radical is very low. The different reactivities of the syn and anti dimer cation radicals are discussed in terms of through-bond coupling between the n orbitals of N(1) and N(1') involving the cyclobutane-ring sigma orbitals. In the cases of the syn-dimers, the sensitizer-dimer ion-radical pairs undergo the rapid geminate recombination that works as a major energy dissipating channel responsible for the lower-than-unity quantum yields. It has been found that the presence of Mg(ClO4)2 at 0.1 M enhances approximately 1.5 times either the monomerization of the syn dimers or the formation of the chloranil anion radical. A laser-flash photolysis study shows that Mg2+ forms a complex with either the triplet or the anion radical of chloranil. The net salt effects are attributed to the retardation of the rapid geminate recombination by the participation of Mg2+ in the sensitizer-dimer ion-radical pairs.

show abstract

Section: Resultsmentioning

confidence: 92%

CHLORANIL‐PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMERS and EFFECT OF MAGNESIUM PERCHLORATE

Pac

Miyamoto

Masaki

et al. 1990

Photochem & Photobiology

View full text Add to dashboard Cite

show abstract

“…It is of mechanistic and biological significance to note that dimer splitting by photoelectron transfer may involve a variety of possible mechanistic channels from ion-radical pairs, as has been shown in photosensitized reactions of some strained compounds by electron acceptors (Jones et al, 1982;Kumar et al, 1984;Borsub and Kutal. 1984;Yamashita et al, 1987).…”

Section: Photorepair Of Uv-damaged Dna and Cyclobutane-ring Splittingmentioning

confidence: 96%

“…Since the stable structure of the triethylamine cation radical is planar, a skeletal change from a pyramidal structure to a planar one should occur upon le-oxidation to allow the possible participation of a rapid decay channel in the electrontransfer process. Rapid geminate recombination of A7D' was mentioned for the inefficient isomerization of quadricyclane to norbornadiene photosensitized by aromatic nitriles in polar solvents (Jones et al, 1982). The isomerization perhaps proceeds as a channel of the rapid electron reversal of A7Df since little dissociation into the free ion radicals was observed.…”

Section: Dynamic and Chemical Behavior Of Geminate Ionradical Pairmentioning

confidence: 99%

“…Since the energy gap for the electron reversal appears to be identical for the contact and loose ion pairs, the different lifetimes might arise from different molecular arrangements between AT and Dt and/or from different solvation of A;/Dt. The chemical behavior of chloraniliarene pairs depends on the photoexcitation wavelengths (Jones et al, 1988). Irradiation at a shorter wavelength edge of the charge-transfer absorption band gives 'hot' A7Df in the singlet spin state which rapidly collapses into a singlet radical pair after proton transfer followed by in-cage radical coupling.…”

Section: Dynamic and Chemical Behavior Of Geminate Ionradical Pairmentioning

confidence: 99%

See 1 more Smart Citation

Electron‐transfer Organic and Bioorganic Photochemistry

Pac

Ishitani

1988

Photochem & Photobiology

View full text Add to dashboard Cite

“…The involvement of these two distinct cation radicals is elegantly demonstrated by CIDNP results in electron transfer (e.g., I -cyanonaphthalene and chloranil) sensitized reactions (16)(17)(18); the potential energy of 4 + ' is estimated to be higher by 9-14 kcal/mol than that of 5+', which drives the one-way isomerization. Extensive studies on similar sensitized interconversions have been published (19).…”

Section: Introduciionmentioning

confidence: 99%

1,3-Diketonatoboron difluoride sensitized cation radical reactions

Chow¹,

Xiang²

1991

Can. J. Chem.

View full text Add to dashboard Cite

Y. L. CHOW and XIANEN CHENG. Can. J. Chem. 69, 133 1 (1991). Dibenzoylmethanatoboron difluoride (DBMBF?) and allied BF2 complexes interact from their singlet excited state with trans-anethole (t-A), quadricyclene (QC), and norbornadiene (NBD) by electron transfer to generate the corresponding cation radicals, which undergo the reported reactions. By sensitization, t-A undergoes dimerization to form the anti head-to-head and syn head-to-head dimers with retention of stereochemistry. The formation is reversible under sensitization conditions, leading to accumulation of the more stable anti isomer. However, irradiation of the absorption band of the DBMBF, -t-A ground state complex did not lead to dimerization of t-A. By DBMBF2 sensitization, QC is cleanly converted to NBD while NBD is not affected. The calculation shows QC+' possesses higher energy than NBD+' by 7.5 kcal/mol, hence an irreversible rearrangement. Other sensitizers (e.g., cyanoaromatics and tetrachlorobenzoquinone) also promote these cation radical reactions but not as cleanly as DBMBF?.

show abstract

Photosensitization of quadricyclene isomerization by electron acceptors. A short-circuit nonradiative decay mechanism for electron donor-acceptor quenching in polar media

Cited by 31 publications

References 0 publications

CHLORANIL‐PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMERS and EFFECT OF MAGNESIUM PERCHLORATE

CHLORANIL‐PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMERS and EFFECT OF MAGNESIUM PERCHLORATE

Electron‐transfer Organic and Bioorganic Photochemistry

1,3-Diketonatoboron difluoride sensitized cation radical reactions

Contact Info

Product

Resources

About