A Molecular Shuttle for Driving a Multilevel Fluorescence Switch

Abstract

A [2]rotaxane-based molecular shuttle comprised a macrocycle mechanically interlocked to a chemical "dumbbell" has been prepared in high yields by a thermodynamically controlled, template-induced clipping procedure. This molecular shuttle has two different recognition sites, namely, -NH2 +- and amide, separated by a phenyl unit. The macrocycle exhibits high selectivity for the -NH2+- recognition sites in the protonated form through noncovalent interactions, which include 1) N+-H...O hydrogen bonds; 2) C-H...O interactions between the CH2NH2+CH2 protons on the thread and the oligo(ethylene glycol) unit in the macrocycle; 3) pi...pi stacking interaction between macrocycle and aromatic unit. Upon deprotonation of the [2]rotaxane the macrocycle glides to the amide recognition site due to the hydrogen bonds between the -CONH- group and the oligo(ethylene glycol) unit in the macrocycle. The deprotonation process requires about 10 equivalents of base (iPr2NEt) in polar acetone, while the amount of base is only 1.2 equivalents in apolar tetrachloroethane. Upon addition of Li+, the conformation of the [2]rotaxane was altered as a result of the collective interactions of 1) hydrogen bonds between pyridine nitrogen and amide hydrogen atoms; 2) coordination between the oligo(ethylene glycol) unit, amide oxygen atom and Li+ cation. Then, when Zn2+ ions are added, the macrocycle returns to the deprotonated -NH- recognition site owing to coordination of the macrocycle and -NH- from the axle with the Zn2+ ion. All the above-mentioned movement processes are reversible through the alternate addition of TFA/iPr2NEt, Li/[12]-crown-4 and Zn2+/ethylenediaminetetraacetate (EDTA), by virtue of hydrogen bonding and metal-ion complexation. Significantly, the three independent movement processes are all accompanied by fluorescent responses: 1) complete repression in the protonated form; 2) low-level expression in the deprotonated form; 3) medium-level expression following addition of Li+; 4) high-level expression on complexation with Zn2+.

A Dual‐Response [2]Rotaxane Based on a 1,2,3‐Triazole Ring as a Novel Recognition Station

“…Interestingly, the macrocycle is able to interact with the two recognition stations when the bridge between them is shortened. Upon deprotonation of both [2]rotaxanes, the macrocycle moves towards the triazole recognition site due to the hydrogen-bond interaction between the triazole nitrogen atoms and the amide groups in the macrocycle. Upon addition of chloride anion, the conformation of [2]rotaxane is changed because of the cooperative recognition of the chloride anion by a favorable hydrogen-bond donor from both the macrocycle isophthalamide and thread triazole CH proton.…”

“…[19] The large dipole (5D) of triazole, the positive end of which points toward the H atom, contributes to its unexpectedly strong hydrogen-bonding capabilities. [19a] Isophthalamide and its derivatives play an important role in [a] Abstract: Two novel multilevel switchable [2]rotaxanes containing an ammonium and a triazole station have been constructed by a Cu I -catalyzed azidealkyne cycloaddition reaction. The macrocycle of [2]rotaxane containing a C6-chain bridge between the two hydrogen bonding stations exhibits high selectivity for the ammonium cation in the protonated form.…”

“…[19a] Isophthalamide and its derivatives play an important role in [a] Abstract: Two novel multilevel switchable [2]rotaxanes containing an ammonium and a triazole station have been constructed by a Cu I -catalyzed azidealkyne cycloaddition reaction. The macrocycle of [2]rotaxane containing a C6-chain bridge between the two hydrogen bonding stations exhibits high selectivity for the ammonium cation in the protonated form. Interestingly, the macrocycle is able to interact with the two recognition stations when the bridge between them is shortened.…”

“…[2] Various external stimuli have been employed to induce such switching, such as ion binding, [3] conformational changes, [4] and alternation of the oxidation state [5] or protonation level of the molecule. [6] Cu Icatalyzed 1,3-dipolar cycloaddition reactions of organic azides and terminal alkynes also called "CuAAC click chemistry" has emerged as a powerful and appealing synthetic tool for the construction of complex materials due to its high efficiency, tolerance of sensitive functional groups, and mild reaction conditions.…”

Dendritic [2]Rotaxanes: Synthesis, Characterization, and Properties

“…11 On the basis of the above structural characteristics by which the dendritic groups were installed on the guest template, the Stoddart group developed a pseudorotaxane-based dendrimer by using a dendritic crown ether and dendritic ammonium. 12 Usually, the template-directed clipping reaction based on 2,6-pyridinedicarboxaldehyde and tetraethylene glycol bis(2-aminophenyl)ether is considered an efficient strategy for the synthesis, in high yields, of all types of rotaxanes, such as linear [2]rotaxanes and oligomers, 13 rectangular [4]rotaxanes, 14 pHinduced switchable rotaxanes, 15 daisy chains, 16 and heterorotaxanes. 17 Recently, we also utilized this approach to efficiently synthesize a series of catenanes.…”