Photochimie à l'État Solide: Réactivité, Structure Cristalline et Fluorescence des Dichloro-1,8 Méthyl-9 et Méthyl-10 Anthracènes

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Abstract
Photoreactivity of the two isomers has been compared in solution as well as in the solid state (microcristalline powder, KBr matrices) and sites of nucleation of the dimers have been investigated by microscopic observation on monocrystals. In solution, 1,8-dichloro 10-methyl anthracene (6) photodimerises faster than its 9-methylated isomer (5). The reverse order of reactivity is observed in the solid state (microcrystals and microcrystalline powder). Crystalline and molecular structure of 6 have been established and compared to that, already known, of 5 in view to interpretate fluorescence spectra (excimer type) and the difference of reactivity. As for several monosubstituted derivatives, the photodimerisation of 5 and 6 is not topochemical but photodimers have been shown to appear in areas of crystalline defects, especially along the c axis in the compound 6. Compacity of crystalline lattices is considered to play a major role in the difference of reactivity.