Photochemical transformations of cis-1,2-dibenzoylalkenes

Lahiri, S. K.; Dabral, V.; Chauhan, S. M. S.; CHAKACHERY, E.; Kumar, Challa V.; Scaiano, J. C.; George, M. V.

doi:10.1021/jo01307a012

Cited by 17 publications

(6 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To confirm that a triplet biradical 2 is formed in the irradiation of the 9,10-ethenoanthracene 1a , as suggested by the 3 O 2 quenching, the influence of molecular oxygen was examined since effective quenching of triplet biradicals by 3 O 2 is well documented in the literature . The Stern−Volmer quenching constant ( k q ) of the transient 2 for 3 O 2 was determined by monitoring the decay rates at various oxygen concentrations (Figure ), and the quenching constant ( k q ) was found to be 6.9 ± 0.2 × 10 8 M -1 s -1 , which is in good agreement with the values reported for similar conjugated biradicals 4 Stern−Volmer oxygen-quenching plot of the transient generated from 1a upon irradiation at 350 nm in benzene solution. …”

Section: Resultsmentioning

confidence: 90%

Photochromic Dibenzobarrlenes: Long-Lived Triplet Biradical Intermediates

et al. 2007

Self Cite

View full text Add to dashboard Cite

Upon exposure to UV light, the disubstituted dibenzobarrelene derivative 1a turns green in the solid phase and reverts back to its original pale-yellow color within several hours in the dark. The lifetime of the colored species in degassed benzene at room temperature is 37 +/- 2 s (Ea for decoloration is 14.5 +/- 0.7 kcal mol-1 and log A is 8.92 +/- 0.5 s-1) and highly sensitive to molecular oxygen; the Stern-Volmer quenching constant is 6.9 +/- 0.2 x 108 M-1 s-1. Similarly, the disubstituted dibenzobarrelenes 1b and 1c exhibited pink coloration when exposed to UV light in the solid phase. On the basis of combined experimental and theoretical evidence, it is proposed that upon photoexcitation the excited singlet state of 1a undergoes rapid intersystem crossing to its triplet state, followed by intramolecular delta-H abstraction, to yield the triplet biradical intermediate (3)2. Upon prolonged irradiation, 2 undergoes cyclization to the alcohol 3, which affords the enone 4 as the final photoproduct. The delta-H abstraction on the triplet-state potential energy surface, calculated at the B3LYP/6-31G* level of density functional theory (DFT), has an activation energy of 18.5 kcal/mol. Further, the absorption spectrum of the triplet biradical (3)2, obtained from time-dependent DFT calculations, displays an intense absorption maximum at 670 nm, which is in good agreement with the observed absorption peak at 700 nm. The molecular-orbital analysis of the triplet diradical (3)2 suggests that its long-wavelength absorption involves the transition of the unpaired electron from the comparatively localized benzyl-type HOMO to the extensively conjugated benzoyl-type LUMO. The present experimental and theoretical results strongly support the intervention of a long-lived triplet biradical (3)2 in the photochromism of appropriately substituted dibenzobarrelenes.

show abstract

Section: Resultsmentioning

confidence: 90%

Photochromic Dibenzobarrlenes: Long-Lived Triplet Biradical Intermediates

et al. 2007

Self Cite

View full text Add to dashboard Cite

show abstract

“…for the Diels-Alder reaction without further purification. 4-U.uohe.u-2-l,namide (9).-A methanolic solution (1 3 ml) of methyl 4-hydroxyhex-2-ynoate (1.99 g) was saturated with ammonia at 0 "C and stirred overnight at room temperature. It was then evaporated to dryness and the residue treated with ether to give the corresponding hydroxy amide (1.23 g, 69%); v,,,,(Nujol) 3 45&3 000, 2 230, 1 660, and 1 610 cm-'.…”

Section: Diels-alder Reactions O F 'mentioning

confidence: 99%

Valence isomer interconversion of norbornadienes and quadricyclanes having an acyl group

Hirao¹,

Yamashita²,

Andõ³

et al. 1988

J. Chem. Soc., Perkin Trans. 1

View full text Add to dashboard Cite

“…19 The end-product in this case is a ketene intermediate, which can lead to a carboxylic acid or ester, depending on whether the reaction is carried out in aqueous or alcoholic medium. 20 We have explored the photochemistry of several 1,2-dicarbonyl systems, including multichromophoric substrates. I shall skip most of these studies and directly come to our detailed investigations on the photochemistry of dibenzobarrelenes.…”

Section: Organic Phototransformationsmentioning

confidence: 99%