Photochemical reactions of anthracene–naphthalene bichromophoric systems linked by a three-carbon chain

Abstract

Photochemical reactions of bichromophoric compounds having 9-anthryl and 1-naphthyl groups linked by a three-carbon chain have been investigated in solution and in the solid state. Direct photolysis of 1a–c,e–g in degassed benzene gave both cyclomers 2a–c,e–g and head-to-tail anthracene dimers 3a–c,e–g through intra- and inter-molecular [4 + 4] cycloaddition, respectively, while 1-acetoxy derivative 1d gave only cyclomer 2d. The reactivity for the cyclomerisation of 1a–g was lower than that of the bisanthracene system. The conjugated carbonyl group in 1e and 1f significantly retarded the reactions. On biacetyl sensitisation neither cyclomerisation nor dimerisation occurred, but alkene 1e underwent cis–trans isomerisation. In the solid state, (E)-1e gave dimer 3e in 22% yield, while the other compounds were photostable or gave the corresponding dimer in a lower yield. X-Ray structure analysis showed that in the crystal of (E)-1e adjacent anthracene rings related by an inversion centre were stacked with 3.45 Å separation, which was favourable for head-to-tail dimerisation.