An unconventional, lockable anthracene photodimer

The synthesis and photochemistry of 1,3-bis- O-(9-anthroyl)-1,3-propanediol is reported. UV irradiation of this compound led to the formation of both intra- and intermolecular photoproducts; unexpectedly, the major product was identified by NMR and X-ray crystallography as a 1,9′-4,10′dianthracene intramolecular cyclomer. The photocyclomer could be prepared in 98% yield and was found to be thermally stable in the dark at room temperature but underwent photochemical reversion to the starting material upon exposure to 285 nm light or via thermal conversion at 80 °C. Epoxidation of the cyclomer locked the molecule in its cyclized form, inhibiting both photochemical and thermal ring-opening.