Controlling selective formation of [2]- and [3]-pseudorotaxanes by tuning spacer length of guests

ABSTRACT Exploration of host–guest complexation between a shape-persistent H-bonded macrocycle and flexible guests may enable construction of new pseudorotaxanes systems. Here, we present the impact of varying the spacer length of four bis(4-phenylpyridinium) guests G1-G4 on production of pseudorotaxanes with a 2D H-bonded macrocycle 1a. The host–guest complexes are probed by 1H NMR, 2D NOESY and UV–vis spectroscopic techniques. [2]- and [3]- pseudorotaxane assemblies are formed specifically using these guests, demonstrating the dependency of accessing [2]- and [3]- pseudorotaxane on the spacer length of these dications. Theoretical calculations reveal the difference in the conformation of the guests between these two binding modes: the one with a 1:1 stoichiometry (spacer length: C4 and C6) show Z-shaped conformation and the other with a 2:1 stoichiometry (spacer length: C8 and C10) take a linear conformation. The findings of the threading modes may help develop new H-bonded macrocycle-based rotaxanes and other related mechanically interlocked molecules. GRAPHICAL ABSTRACT