Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
The Photoisomerization of cis-Azobenzene in the Presence of Iodine
Shigeru YamashitaDesmond P. CosgraveHiroshi OnoOsamu Toyama
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1963 Volume 36 Issue 6 Pages 688-692


The conversion of cis-azobenzene in a n-hexane solution to its trans-isomer in the presence of iodine has been studied by light irradiation. The experiments with wavelengths of 313 and 436 mμ at −78°C have shown that the excitation of the molecular complex formed between cis-azobenzene and iodine, by its charge-transfer transition or by the blue-shifted absorption of complexed iodine, yields trans-azobenzene with a quantum yield independent of the composition of the solution. By comparing this finding with the results previously obtained for the cis-trans photoiso-merization of free azobenzene in n-hexane, a probable mechanism has been presented: CI2 + hν → CI2*, CI2* → C* + I2 and C* → T, where C and T denote cis and trans-eizoben-zene respectively.
The results obtained at 0°C by irradiation at wavelengths of 546 and 577 mμ, which are solely absorbed by free iodine in the solution, are similar to those previously obtained for stilbene; they may, therefore, be explained in a similar way, i. e., by the photochemical dissociation of free iodine, followed by the iodine atom-catalyzed isomerization of cis-azobenzene.

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