Redox Switchable Daisy Chain Rotaxanes Driven by Radical–Radical Interactions

Abstract

We report the one-pot synthesis and electrochemical switching mechanism of a family of electrochemically bistable 'daisy chain' rotaxane switches based on a derivative of the so-called 'blue box' (BB(4+)) tetracationic cyclophane cyclobis(paraquat-p-phenylene). These mechanically interlocked molecules are prepared by stoppering kinetically the solution-state assemblies of a self-complementary monomer comprising a BB(4+) ring appended with viologen (V(2+)) and 1,5-dioxynaphthalene (DNP) recognition units using click chemistry. Six daisy chains are isolated from a single reaction: two monomers (which are not formally 'chains'), two dimers, and two trimers, each pair of which contains a cyclic and an acyclic isomer. The products have been characterized in detail by high-field (1)H NMR spectroscopy in CD3CN-made possible in large part by the high symmetry of the novel BB(4+) functionality-and the energies associated with certain aspects of their dynamics in solution are quantified. Cyclic voltammetry and spectroelectrochemistry have been used to elucidate the electrochemical switching mechanism of the major cyclic daisy chain products, which relies on spin-pairing interactions between V(•+) and BB(2(•+)) radical cations under reductive conditions. These daisy chains are of particular interest as electrochemically addressable molecular switches because, in contrast with more conventional bistable catenanes and rotaxanes, the mechanical movement of the ring between recognition units is accompanied by significant changes in molecular dimensions. Whereas the self-complexed cyclic monomer-known as a [c1]daisy chain or molecular 'ouroboros'-conveys sphincter-like constriction and dilation of its ultramacrocyclic cavity, the cyclic dimer ([c2]daisy chain) expresses muscle-like contraction and expansion along its molecular length.

Photocontrolled Reversible Conversion of Nanotube and Nanoparticle Mediated by β‐Cyclodextrin Dimers

“…After cooling to room temperature,t he mixture was filtered to remove any insoluble copper salt, and the filtrate was evaporatedu nder reduced pressure to remove excess DMF.T he residue was purified by silica gel column chromatography using chloroform-methanol solution (v/v = 50:1) as elutent to give azobenzene-bridged bis(permethyl-b-CD) (71 %) as orange foam (yield 71 %). 2,147.3,143.0,125.1,124.4,114.8,99.2,98.8,98.3,83.0,82.0,81.9,81.8,81.1,80.3,80.2,79.9,79.3,71.28,71.0,70.8,70.7,70.3,62.2,61.8,61.4,61.3,59.2,59.1,59.0,58.9,58.7,58.6,58.5,58.4, Keywords: conversion ·p hotochemistry ·p hotocontrol · self-assembly ·supramolecular chemistry 13 CNMR (100 MHz, CDCl 3 ): d = 160.…”

“…Controllable supramolecular nanoassembly has attracted increasing attention due to its wide application in the fields of catalysis, [1] nanoscience, [2] and drug delivery. [3] Supramolecular assembling is an effective approach for the construction of controllable nanoscaled assemblies [4] that are responsive to various external stimuli, such as temperature,p H, redox conditions,enzymes,and light.…”

Controlling Motion at the Nanoscale: Rise of the Molecular Machines

“…Many stimuli may be used to actuate motion in these efficient and versatile switches including pH, redox reactions, light, solvent, and ions. [131][132][133][134][135] Efforts have been made to polymerize daisy-chain rotaxanes into linear assemblies with varying success. 136,137 In one of the most remarkable examples, Giuseppone, Buhler, and co-workers demonstrated a metallo-supramolecular polymerization process to combine thousands of pHswitchable daisy-chain rotaxanes.…”

Electrochemically addressable trisradical rotaxanes organized within a metal–organic framework

“…It is only in their radical cation redox states that favorable interactions (47)(48)(49)(50)(51)(52)(53)(54)(55)(56) between the electrons of the viologen centers bring the components together to form (Fig. 4B) the trisradical semirotaxane 1…”