229173-16-4Relevant articles and documents
Biradical intermediates in the photoisomerization of dibenzodihydropentalenofurans to dibenzosemibullvalenes
Sajimon,Ramaiah,Thomas,George
, p. 3182 - 3187 (2001)
The photoisomerization of a few substituted dibenzodihydropentalenofurans to the corresponding dibenzosemibullvalenes is reported. Steady-state photolysis of the dibenzodihydropentalenofurans 3a-d gave the corresponding dibenzosemibullvalenes 2a-d in nearly quantitative yields. The quantum yields of this photoisomerization were found to be in the range 0.17-0.26. Laser flash photolysis studies of the dibenzodihydropentalenofurans 3a-e showed transients, with absorption maxima around 410 nm and decaying by first-order kinetics. The lifetimes were in the range 14-30 μs in degassed benzene at 25 °C. These transients were readily quenched (trapped) by molecular oxygen, and the Stern-Voelmer quenching constants were found to be in the range (2.45-3.17) × 109 M-1 s-1. As a representative example, the 1,3-biradical intermediate from 3e was trapped by molecular oxygen to give the corresponding endoperoxide 11e. The transients were weakly quenched by triplet/radical quenchers such as 2,2,6,6-tetramethylpiperinyl-1-oxy (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperinyl-1-oxy (HTEMPO), and the quenching constants are found to be in the range (1.09-3.19) × 106 M-1 s-1. The decay rates of the transients were found to be temperature dependent and obeyed the Arrhenius equation. For example, the activation energy of the transient from 3a was ～4.5 kcal mol-1 and the Arrhenius preexponential factor log(A/s-1) for the decay of the transients was ～7.5. On the basis of our studies, these transients were assigned as the ground-state triplet biradicals, generated by the cleavage of the C-O bond of the starting dibenzodi-hydropentalenofurans.
Photoisomerization of bridgehead monosubstituted dibenzobarrelenes and interesting thermal isomerization of their photoproducts
Sajimon, Meledathu C.,Ramaiah, Danaboyina,Muneer, Mohammed,Ajithkumar,Rath, Nigam P.,George, Manapurathu V.
, p. 6347 - 6352 (2007/10/03)
Phototransformations of a few bridgehead monosubstituted dibenzobarrelenes, 4a-d, and thermal isomerizations of their primary photoproducts, 7a and 11a-c, are described. Irradiation of 4a in benzene gave a mixture of regioisomeric products, 7a (8b-isomer)
