Direct Synthesis of an Oligomeric Series of Interlocked, Cyclodextrin‐Based [c2]Daisy Chains

Abstract

Despite their anticipated utility and aesthetic appeal, attempts to prepare extended molecular daisy chains have been thwarted by preferential formation of cyclic dimers ([c2]‐rotaxanes). Previously, to circumvent this limitation, an alternative type of molecular chain has been synthesized by linking pre‐prepared [c2]rotaxanes already interlocked with bulky capping groups. Instead of this stepwise approach, here we describe the direct self‐assembly of dimeric complexes and their in situ oligomerization, which simultaneously interlocks the dimers so that no prior capping of the complexes is required. Eight individual supramolecular species, including a tetramer, hexamer, octamer and decamer series, have been isolated and characterized. The decamer is derived from 16 molecular components, through ten highly selective reactions of six equivalents of the bifunctional linking reagent with five self‐assembled dimeric cyclodextrin inclusion complexes, all in one pot.

Daisy chain architectures: from discrete molecular entities to polymer materials

“…More recently, using identical host and guest moieties, the group of Easton reported the one-pot synthesis of [c2]daisy chain oligomers (up to the pentamer) from an a-cyclodextrin/azobenzene conjugate in the presence of an activated ester of suberic acid (entry 2, Table 3). 83 Interestingly, this one-pot strategy also afforded cyclized 3). 84 The resulting double bond was then reduced using platinum oxide and hydrogen, and the axle was modified with 4-pentenoic acid at the end chains.…”

“…More recently, using identical host and guest moieties, the group of Easton reported the one-pot synthesis of [ c 2]daisy chain oligomers (up to the pentamer) from an α-cyclodextrin/azobenzene conjugate in the presence of an activated ester of suberic acid (entry 2, Table 3). 83 Interestingly, this one-pot strategy also afforded cyclized [ c 2]daisy chain architectures composed of one or two interlocked molecules. For all isolated species, light-induced contraction and extension occurred, albeit with lower degree of isomerization at the photostationary state in water compared to methanol solutions.…”

Molecular Actuation of a Bistable Liquid‐Crystalline [c2]Daisy Chain Rotaxane

“…[12][13][14][15][16][17] Of particular interest, the interlocked topology of [c2]daisy chain rotaxanes has been inspired by the sliding movement that takes place inside a sarcomere, the basic contracting unit of our muscles. [18,19] When made bistable, [c2]daisy chain rotaxanes can undergo a molecular extension / contraction switching process controlled by external stimuli (e. g. pH, [20,21] redox potential, [22] solvent, [23] or light [24,25] ). [26,27] In principle, when coupling many of these tiny MIMs with one another in space and time, their movements can be transferred and amplified from molecular to higher length scales, [28] with the potential to access an infinity of new dynamic and active systems with responsive properties.…”

Cyclodextrin‐Based [c2]Daisy Chain Rotaxane Insulating Two Diarylacetylene Cores

“…Several research groups have previously developed synthetic methodsf or [c2]daisy chain rotaxanes, [6][7][8] wherein two subunits bearing both axle and ring componentsa re associatedb y threading each axle through the other ring to form ap seudo[2]rotaxane that is mechanicallyi nterlocked by capping with bulky terminalg roups ( Figure 1b). This strategy is efficient for symmetric pseudo[2]rotaxane formation because the hostguest interactions between the two subunits are doubled, as each unit includes both host (ring) and guest (axle) moieties.…”

“…This is ac haracteristicb ehavior of [c2]daisy chain rotaxane,a lso knowna st he molecular muscle. [6][7][8]13] When the two diarylacetylene cores are in close proximity,a ne xcimer can form, resulting in excimer emission;o therwise, monomer emission occurs. These results imply that contraction and extension of the [c2]daisy chain structure of rotaxane 2 occurs in solution by shuttling the PM a-CDs along the axle components.…”