Abstract
Molecular tweezers are artificial receptors that have an open cavity generated by two recognition units pre-organized by a spacer. Switchable molecular tweezers, using a stimuli-responsive spacer, are particularly appealing as prototypes of the molecular machines that combine mechanical motion and allosteric recognition properties. In this present study, the synthesis of switchable molecular tweezers composed of a central terpyridine unit substituted in 4,4″ positions by two Pt(II)-salphen complexes is reported. The terpyridine ligand can be reversibly converted upon Zn(II) coordination from a free ‘U’-shaped closed form to a coordinated ‘W’ open form. This new substitution pattern enables a reverse control of the mechanical motion compared to the previously reported 6,6″ substituted terpyridine-based tweezers. Guest binding studies with aromatic guests showed an intercalation of coronene in the cavity created by the Pt-salphen moieties in the closed conformation. The formation of 1:1 host-guest complex was investigated by a combination of NMR studies and DFT calculations.
Highlights
The concept of molecular tweezers was first introduced by Whitlock [1] who defined a molecular receptor characterized by two flat, generally aromatic, recognition sites pre-organized by a spacer to create an open cavity
Rigid or semi-flexible spacers have so far been the most frequently used in the design of molecular tweezers, mostly for molecular recognition purposes [2,3,4,5,6,7,8,9,10]
We have developed a family of switchable molecular tweezers based on a terpyridine unit substituted by metal salphen complexes with different properties depending on the metallic ion coordinated to the salphen ligand
Summary
The concept of molecular tweezers was first introduced by Whitlock [1] who defined a molecular receptor characterized by two flat, generally aromatic, recognition sites pre-organized by a spacer to create an open cavity. We have developed a family of switchable molecular tweezers based on a terpyridine unit substituted by metal salphen complexes with different properties depending on the metallic ion coordinated to the salphen ligand. By using a 6,6” substituted terpyridine, the tweezers can switch upon metal coordination from a “W”-shaped open form to a “U” closed form, which brings the two salphen moieties in close spatial proximity (Figure 1). This controlled and large modification of the distance between the two functional units has been successfully applied to modulate magnetic [28,29].
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