9-Anthroylacetone and its photodimer

Abstract 9-Anthroylacetone undergoes a head-to-tail [4π+4π] 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 yields >0.023 mol/Einstein are evaluated for the solid state reaction. Interestingly, the dimer dissociates to give 9-anthroylacetone, both thermally ( T >130 °C) and photochemically, by short UV wavelength irradiation. The single-crystal X-ray structure of 9-anthroylacetone and its dimer are reported.