9-Anthroylacetone and its photodimer

9-Anthroylacetone undergoes a head-to-tail [4pC4p] photo-dimerisation reaction that leads to the formation of 5,11-bis(1,3- diketobutyl)-5,6,11,12-tetrahydro-5,12,6,11-di-o-benzeno-dibenzo[a,e]cyclooctene both in solution and in the solid state when irradiated with different sources (sunlight, tungsten lamp, xenon lamp, UV laser beam 351-364 nm), the reaction being accompanied by a colour variation from bright yellow to colourless. Quantum yieldsO0.023 mol/Einstein are evaluated for the solid state reaction. Interestingly, the dimer dissociates to give 9-anthroylacetone, both thermally (TO130 8C) and photochemically, by short UV wavelength irradiation. The single-crystal X-ray structure of 9-anthroylacetone and its dimer are reported. q 2004 Elsevier Ltd. All rights reserved.