Structure of supramolecular complex of flexible molecular tweezers and planar guest in solution

Flexible molecular receptors having three aromatic chromophores can bind electron deficient planar guests both in the crystalline state and in solution. The crystalline complex has a triple-decker type donor–acceptor–donor sandwich arrangement in which the guest located between the two terminal aromatic chromophores of the host. Two orientations of the guest, parallel and cross, with respect to the phenanthrene ring of the host were predicted by a molecular mechanics calculation. The former structure was found in the crystalline state. Although the latter was predicted to be less stable, the observed complexation induced shift of the guest supports this orientation in solution. When the terminal naphthalene ring of the host was changed to a benzene ring, the stoichiometry of the crystalline complex changed either to 1:2 or 2:1 depending on the guest.