A Ferrocene‐Functionalized Bistable [2]Rotaxane with Switchable Fluorescence

Abstract

A switchable, bistable molecular shuttle based on dialkylammonium ion and urea functional recognition sites, and a macrocycle bearing a ferrocenyl unit has been constructed, in which the ferrocenyl macrocycle can be easily switched along the thread by addition of acid/base or by addition/removal of acetate anions. The shuttling motion of the macrocycle is accompanied with different fluorescence responses via the adjustment of the photoinduced electron transfer (PET) effect between the ferrocene electron donor and the fluorophores.Mechanically interlocked molecules (MIMs), [1] in particular functional bistable [2]rotaxanes, have attracted much attention in the past few decades due to their challenging construction and potential applications as an excellent framework for the fabrication of molecular machines, such as molecular switches and probes. [2] The shuttling motion of the macrocycle between different recognition sites on the rotaxane thread can be driven by acid/base, [3] ion binding, [4] altering the oxidation state, [5] photochemistry, [6] and solvent changes. [7] Some of these shuttling motions are usually accompanied with remarkable changes in physical properties, such as circular dichroism, [8] conductivity, [9] and fluorescence. [10] Among them, fluorescence change is preferably used as an output signal since it can be easily and remotely detected with low cost.Recently, some successful examples based on bistable [2]rotaxanes with excellent fluorescence responses have been developed, [10] for example, a typical [2]rotaxane with a fluorescent response toward the shuttling movements was reported by Tian and co-workers in 2004. [10a] With further research for switchable rotaxane-containing fluorophores, ferrocene-modified rotaxane attracted more and more attention. [10f, g, k-m] A pyrene/ferrocene-based [2]rotaxane with a three-level lumines-cent response was reported by Mateo-Alonso et al., [10f] and a ferrocene-functionalized molecular shuttle was constructed by Qu and co-workers, in which the fluorescence of the rotaxane can be reduced or enhanced alternately by an adjustable photoinduced electron transfer (PET) process occurring between two ferrocene (Fc) units in the macrocycle and two fluorescent stoppers. [10l] However, it is still a challenge to construct systems in which the shuttling motion of the macrocycle is accompanied with different fluorescence responses, and surely this system would pave the way for constructing more complicated and delicate multilevel molecular switches with optical signals.On the basis of the above-mentioned works and our recent work on a phosphine-oxide-based, three-station molecular shuttle, [4d] and in continuation of research on molecular shuttles, herein we describe an acid/base and anion-responsive bistable molecular shuttle bearing an anthracene stopper on the thread and a ferrocenyl unit on the macrocycle, in which two different states are obtained by using external stimuli (acid/ base and anions). As a result, the fluorescence can be reduced or enhan...

Co‐conformational Exchange Triggered by Molecular Recognition in a Di(acylamino)pyridine‐Based Molecular Shuttle Containing Two Pyridine Rings at the Macrocycle

“…[9][10][11][12] Amongst these compounds, molecular shuttles having ar otaxane architecture play an essential role in the molecular machinery toolbox as switchable components. [13][14][15][16][17][18][19] Thus, the relative movement of their threaded components can be controlledb yt he incorporation of binding sites with exchangeable affinitiesi ns trategic positions along the axle and macrocycle. [8] Control of submolecular motion in molecular shuttlesc an be triggered by aw ide variety of stimuli, including redox, photochemical or acid-base processes.…”