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The thermal monomerization of 9-cyanoanthracene photodimer (9CNAD) single crystals has been studied using differential scanning calorimetry (d.s.c.) jointly with emission spectroscopy of cleaved surfaces of partially monomerized 9CNAD single crystals. The first exothermic peak, together with the subsequent peaks, is attributed to monomer crystallization inside the photodimer host matrix and not to directional reaction along a certain family of planes as recently reported. The photoreactivity of the developing microcrystallites has been studied and the energy of activation for their photoredimerization is dependent upon the conditions of their generation. The energy of activation for the photodimerization of 9-cyanoanthracene incipient dimer pairs has also been evaluated and is consistent with a homogeneous topochemical reaction.
Ebeid et al. (1983) studied this question.