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.

本文报道了一种基于三联吡啶-镍-双水杨醛缩邻苯二胺配合物（terpyridine(Ni-salphen)₂）分子镊子的六态分子开关，该开关可通过三种正交刺激（金属配位、氧化还原反应与客体结合）实现精准寻址调控。通过金属配位刺激，该分子镊子可发生机械构象转变，从开放的“W”形结构切换至闭合的“U”形结构。上述两种状态均可通过氧化还原刺激实现可逆氧化，且均可与吡嗪客体结合，由此额外生成四种状态。全部六种状态均具备良好稳定性，且可通过恰当的刺激组合实现制备与调控，并已通过核磁共振波谱（Nuclear Magnetic Resonance, NMR）、X射线衍射（X-ray Diffraction, XRD）、电子顺磁共振波谱（Electron Paramagnetic Resonance, EPR）以及密度泛函理论（Density Functional Theory, DFT）计算开展了系统表征与研究。将机械运动与客体结合的超分子设计理念，与Ni-salphen配合物的氧化还原非惰性及价态互变异构特性相结合，为机械分子开关新增了两个调控维度。