Light‐Induced Cyclization of A [c2]Daisy‐Chain Rotaxane to Form a Shrinkable Double‐Lasso Macrocycle

Abstract

Ap H-responsive double-lasso macrocycle has been successfully obtained directly from a[ c2]daisyc hain rotaxane via ap hotodimerization reaction of two terminal coumarin ligands. The size of the double-lasso macrocycle could be tuned by acid/base stimuli with the reversible muscle-likee xtension/contraction of the [c2]daisyc hain unit.Scheme1.Synthetic route to double-lasso macrocycle 1 containing[ c2]daisy chain rotaxane. The coumarin unit formed after photodimerization has four isomerso wing to cycloaddition, and only one of them is shownh ere.

[ c 2]Daisy Chain Rotaxanes as Molecular Muscles

“…As expected, deprotonation of the ammonium triggers the contraction of the extended lasso to a tighter one, a motion that can be reversed by the addition of acid. A similar structure was recently reported by the group of Qu, 51 making use of a cyclization mechanism based on the photodimerization of coumarin molecules. One should also notice that, following an original line of research, the group of Mayor 52 developed the first strategy to produce [c2] and [a2]daisy chains in an aqueous environment by inserting a negatively charged oligo(phenylene-ethynylene) (the axle) into a positively charged ammonium cyclophane (the macrocycle), thanks to electrostatic interactions and the hydrophobic effect.…”

The Mobility of Homomeric Lasso‐ and Daisy Chain‐Like Rotaxanes in Solution and in the Gas Phase as a Means to Study Structure and Switching Behaviour

“…In the example of Qu and coworkers, the shrinkable double‐lasso macrocycle 11a was prepared from a crown ether‐based [ c2 ]daisy chain rotaxane in which both thread motifs are connected through a coumarin unit (Figure 5). [22] In the contracted form, the macrocycles reside on the ammonium stations. Deprotonation using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) afforded the extended isomer 11b , in which the macrocycles encircle the imidazolium stations.…”

“…In the last decade, two research groups have reported the synthesis of a double-lasso macrocycle starting from a [c2]daisy chain rotaxane, [21,22] in which the conversion between extended and contracted isomers was studied by DOSY experiments. In the example of Qu and coworkers, the shrinkable double-lasso macrocycle 11a was prepared from a crown ether-based [c2]daisy chain rotaxane in which both thread motifs are connected through a coumarin unit (Figure 5).…”

“…Exchange of the extended and contracted forms of doublelasso macrocycle 11. [22] Figure 6. Chemical structure of: a) [1]rotaxane 12; and b) macrocycle 13.…”

Post‐Synthetic Macrocyclization of Rotaxane Building Blocks

“…A second example of cyclic molecular muscle was reported later by Qu and co-workers from the isolated [c2]daisy chain rotaxane dimer 25 (Scheme 7b). [35] The authors used coumarins as photochemical self-connecting moieties for the postsynthetic linking of the two extremities of the rotaxane dimer. The mechanical bond of the doubly interlocked molecular architecture 25 was ensured by the bulky meta-dimethoxyaryl units.…”