Porphyrin-Based Switchable Molecular Turnstiles

The design, synthesis and structural characterisation, in solution, of two new molecular turnstiles based on Sn-porphyrin derivatives are described. The system is composed of a stator (5-(4-pyridyl)-10,15,20-triphenylporphyrin), a hinge (Sn-IV) and a rotor (handle equipped with 2,6-pyridinedicarboxamide as a tridentate coordinating site or its Pd-II complex). The presence of interaction sites, both on the stator and the rotor, offers the possibility of switching between an open state (free rotation of the handle around the porphyrin) and a closed state (blockage of the rotation) by either establishment of hydrogen bonds between the stator and the rotor or by the simultaneous binding of Pd by both coordinating groups.