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Thermochemical and Photochemical Aspects of the Valence Isomerization of 9-ter-butylanthracene

The exothermicity of the valence isomerization of 1-tert-butyldibenzo-2, 5-bicyclo(2.2.0)hexadien[9-tert-butyl-9, 10-(Dewar-anthracene)] to 9-tert-butylanthracene in n-hexane was determined by calorimetry to  Hf=37 2 kcal/mol. The activation enthalpy  H# 23.6 1.4 kcal/mol and the entropy  S#=0.26 4.4 e.u. are in agreement with the kinetic data for the aromatization of other Dewar isomers. Photoisomerization of 9-tert-butylanthracene to the Dewar isomer 9-tertbutyl-9, 10-(Dewar-anthracene) was observed in aerated aqueous miccelar solutions at room temperature. The triplet state of 9-tert-butylanthracene was detected by nanosecond laser photolysis as well as indirectly by the measurement of singlet oxygen produced in a reaction between the triplet state of 9-tert-butylanthracene and molecular oxygen. The quantum yield of formation of the triplet state of 9-tert-butylanthracene was dertermined to be 17 times smaller than the quantum yield of the triplet formation of anthracene.

chemistry; multidisciplinary

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