A Chemically and Electrochemically Switchable [2]Catenane Incorporating a Tetrathiafulvalene Unit

Abstract

A mechanical switch in a [2]catenane, made up of a cyclobis(paraquat-p-phenylene) tetracation interlocked with a macrocyclic polyether containing a redox-active tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene ring system, can be thrown either chemically or electrochemically. The neutral TTF unit resides "inside" the tetracationic cyclophane in the reduced state and "alongside" it in the oxidized species (TTF / TTF ). Switching between the reduced (I ) and oxidized state (I (I )) is accompanied by a dramatic color change.

Measurement of the ground-state distributions in bistable mechanically interlocked molecules using slow scan rate cyclic voltammetry

“…Scanning at slower and slower scan rates, a new oxidation peak becomes increasingly apparent, until, upon using a scan rate of 10 mV s −1 , a new reversible redox process is observed with a redox potential of þ0.49 V. In the case of C1 4þ (Fig. 3B), which was first reported (19) in 1998, the ground-state distribution constant has never been measured carefully. CV experiments, however, suggest that the value must be significantly greater than approximately 10 as a consequence of the fact that the anodic peak corresponding to the MSCC of this bistable catenane could not be observed in the ground state at equilibrium.…”

“…R 4þ along with C1 4þ both contain DNP as the alternative π-electron-rich unit, whereas C2 4þ incorporates the much less π-electron-rich butadiyne unit. C1 • 4PF 6 (19) and C2 • 4PF 6 (20) were both synthesized using previously reported literature procedures, employing templatedirected protocols in the final step to achieve the mechanically interlocked compounds. R • 4PF 6 was obtained (34) using a threading-followed-by stoppering approach (35), making use of the copper(I) catalyzed 1,3-dipolar cycloaddition (36, 37) between the azide-terminated thread and the alkyne functionalized stopper precursor.…”

“…The catenanes C1 • 4PF 6 (19) and C2 • 4PF 6 (20) were prepared according to literature procedures. Both analytical and preparative HPLC were performed on reverse-phase (RP-HPLC) instruments, using C 18 columns and a binary solvent system (MeCN and H 2 O with 0.1% CF 3 CO 2 H).…”

“…Gaining intimate knowledge of the mechanisms (15)(16)(17)(18) governing the relative molecular motions of their components is, therefore, a pursuit that yields crucial information for the design of artificial molecular machines. Bistable mechanically interlocked molecules (MIMs) [namely, bistable catenanes (19,20) and rotaxanes (21), whose syntheses are often templated by noncovalent bonding interactions that "live-on" in the MIMs] have experienced a frenzy of intense research activity in recent years. This attention is in part a consequence of the fact that bistable switchable MIMs possess the inherent ability to gain precise control over the relative motions of their mechanically interlocked components.…”

Mechanostereochemistry and the mechanical bond

“…These MIMs include (figure 8c,d) a branched [7]catenane 36 (Amabilino et al 1997), well-defined oligorotaxanes 37 which fold in solution (Basu et al 2011), and numerous switchable MIMs, based on the redox-active electron donor tetrathiafulvalene (TTF) (Asakawa et al 1998). In addition, Sanders and co-workers have expanded the donor-acceptor toolkit, preparing MIMs with pyromellitic diimide and naphthalene diimide units as the electron-deficient components; these units have led to the synthesis of neutral donoracceptor MIMs (Hamilton et al 1998).…”