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Molecules and materials that demonstrate large amplitude responses to minor changes in their local environment play an important role in the development of new forms of nanotechnology. Molecular daisy chains are a type of a mechanically interlocked molecule that are particularly sensitive to such changes in which, in the presence of certain stimuli, the molecular linkage enables muscle‐like movement between a reduced‐length contracted form and an increased‐length expanded form. To date, all reported syntheses of molecular daisy chains are accomplished via passive‐template methods, resulting in a majority of structures being switchable only through the addition of an exogenous stimuli such as metal ions or changes in pH. Here, we describe a new approach to these structural motifs that exploits a multi‐component active‐metal template synthesis to mechanically interlock two pi‐rich nanohoop macrocycles into a molecular daisy chain that undergoes large conformational changes using thermal energy. 

Addition of the bipyridyl‐embedded cycloparaphenylene nanohoop bipy[9]CPP to [Fe{H₂B(pyz)₂}] (pyz=pyrazolyl) produces the distorted octahedral complex [Fe(bipy[9]CPP){H₂B(pyz)₂}₂] (1). The molecular structure of1shows that the nanohoop ligand contains a non‐planar bipy unit. Magnetic susceptibility measurements indicate spin‐crossover (SCO) behaviour with aT_1/2of 130 K, lower than that of 160 K observed with the related compound [Fe(bipy){H₂B(pyz)₂}₂] (2), which contains a conventional bipy ligand. A computational study of1and2reveals that the curvature of the nanohoop leads to the different SCO properties, suggesting that the SCO behaviour of iron(II) can be tuned by varying the size and diameter of the nanohoop.

 

Addition of the bipyridyl‐embedded cycloparaphenylene nanohoop bipy[9]CPP to [Fe{H₂B(pyz)₂}] (pyz=pyrazolyl) produces the distorted octahedral complex [Fe(bipy[9]CPP){H₂B(pyz)₂}₂] (1). The molecular structure of1shows that the nanohoop ligand contains a non‐planar bipy unit. Magnetic susceptibility measurements indicate spin‐crossover (SCO) behaviour with aT_1/2of 130 K, lower than that of 160 K observed with the related compound [Fe(bipy){H₂B(pyz)₂}₂] (2), which contains a conventional bipy ligand. A computational study of1and2reveals that the curvature of the nanohoop leads to the different SCO properties, suggesting that the SCO behaviour of iron(II) can be tuned by varying the size and diameter of the nanohoop.