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Activation parameters for the photocycloreversion of heterocoerdianthrone endoperoxide in the condensed phase

✍ Scribed by K. Jesse; F.J. Comes; R. Schmidt; H.-D. Brauer

Publisher
Elsevier Science
Year
1989
Tongue
English
Weight
419 KB
Volume
160
Category
Article
ISSN
0009-2614

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✦ Synopsis

The temperature dependence of the photocycbreversionof the endoperoxide (HCDPO) of heterocoerdianthrone (HCD) yielding HCD and IO2 has been studied. Steady-state experiments show that the quantum efficiency for this process is not influenced by temperature in the wavelength region where the $(mr*) and S4(xx*) bands overlap. Time-resolved measurements with the pump-probe technique were carried out in the solvents chlorobenzene and toluene. The rise time for ACD formation decreases with increasing temperature by about a factor 6 in the range 0-60°C. Fitting the data to an Arrhenius relation gives an activation energy of 5.3 + 0.7 kcal/mol in chlorobenzene and 5.7 kO.9 kcal/mol in toluene. The results are consistent with a solvent-independent two-step photofragmentation of HCDPO with an activation-controlled second step.

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