Six States Switching of Redox-Active Molecular Tweezers by Three Orthogonal Stimuli

A six
level molecular switch based on terpyridine­(Ni-salphen)2 tweezers and addressable by three orthogonal stimuli (metal
coordination, redox reaction, and guest binding) is reported. By a
metal coordination stimulus, the tweezers can be mechanically switched
from an open “W”-shaped conformation to a closed “U”-shaped
form. Theses two states can each be reversibly oxidized by the redox
stimulus and bind to a pyrazine guest resulting in four additional
states. All six states are stable and accessible by the right combination
of stimuli and were studied by NMR, XRD, EPR spectroscopy, and DFT
calculations. The combination of the supramolecular concepts of mechanical
motion and guest binding with the redox noninnocent and valence tautomerism
properties of Ni-salphen complexes added two new dimensions to a mechanical
switch.