Studies of the Preparation of Pi-Extended Anthracenes and their Reactivity with an Emphasis on their Photo reactivity
Both 9,10-diaryl and 9,10-diarylethenyl substituted Anthracenes have recently been forwarded as light-regulated semiconducting materials, as well as potential constituent molecules in light-harvesting devices for the organic solar cell applications. So, it is of importance to understand whether such 9,10-substituted Anthracenes are stable under photo-irradiation for a long time, and what type of reactions they could undergo. In the present thesis, photochemistry of 9-anthranylacrylates and 9-aroylethenylanthracenes has been investigated. Anthranylacrylates and 9-aroylethenylanthracenes have been prepared by Wittig-olefination reaction from 9-anthranylcarbaldehyde. Bromination of these molecules was found to give an access to 10-aryl-9-aroylethenylanthracenes after Suzuki-Miyaura coupling reactions. While 9-ethenyl-substituted Anthracenes in principle could undergo a photochemical [2+2] cycloaddition through their ethenyl unit or a photochemical [4+4] dimerisation via their anthranyl core unit, our result showed a photochemical E-Z-isomerisation of the ethenyl substituent in the case of the 9-aroylethenylanthracenes, while the anthranyl acrylates showed a slow photochemically induced polymerization. In order to "protect" the anthranyl unit, the 9-ethenylanthracenes were submitted to Diels-Alder reactions. The cycloadducts were subjected to photo-irradiation, also. In all, 9-ethenylanthracenes were found to be photoreactive under UV -irradiation. This could lead to the degradation of ethenylanthracene-containing materials; it should be taken into account when using these conditions.