Photochemical generation of benzene–naphthalene biplanemers

A direct biplanemer synthesis could be achieved by a quantitative [4π+4π]photocycloaddition of benzyloxy substituted benzene and naphthalene rings (3d,e ⇄ 4d,e). Since the products do not show a thermal Cope rearrangement—in contrast to the related longicyclic conjugated 9,10-benzotricyclo[4.2.2.22,5]dodeca-3,7,9-trienes—but a quantitative reverse reaction, they are interesting systems for an optical switching.