Pyridyl-Acyl Hydrazone Rotaxanes and Molecular Shuttles

We report on rotaxanes featuring a pyridyl-acyl hydrazone moiety on the axle as a photo/thermal-switchable macrocycle binding site. The pyridyl-acyl E-hydrazone acts as a hydrogen bonding template that directs the assembly of a benzylic amide macrocycle around the axle to form [2]­rotaxanes in up to 85% yield; the corresponding Z-hydrazone thread affords no rotaxane under similar conditions. However, the E-rotaxane can be smoothly converted into the Z-rotaxane in 98% yield under UV irradiation. The X-ray crystal structures of the E- and Z-rotaxanes show different intercomponent hydrogen bonding patterns. In molecular shuttles containing pyridyl-acyl hydrazone and succinic amide ester binding sites, the change of position of the macrocycle on the thread can be achieved through a series of light irradiation and heating cycles with excellent positional integrity (>95%) and switching fidelity (98%) in each state.本研究报道了一类轴上带有吡啶酰腙（pyridyl-acyl hydrazone）官能团的轮烷（rotaxanes），该官能团可作为光/热可逆的大环结合位点。吡啶酰腙的E型异构体可作为氢键模板，引导苄基酰胺大环环绕轴链组装，以最高85%的产率得到[2]轮烷；而在相同条件下，带有Z型酰腙的轴链无法生成轮烷。不过，E型轮烷可在紫外照射下以98%的产率顺利转化为Z型轮烷。E型与Z型轮烷的X射线晶体结构显示二者具有不同的组分间氢键作用模式。在同时含有吡啶酰腙与琥珀酰胺酯结合位点的分子梭（molecular shuttles）中，可通过一系列紫外照射与加热循环实现大环在轴链上的位置切换，且各状态下的位置完整性均大于95%，切换保真度达98%。