Sequence‐controlled synthesis of rotaxanes

Abstract

Rotaxanes with well-defined ring sequences are attractive synthetic goals in the construction of functional materials associated with molecular shuttles and switches, molecular electronics, and information storage. Sequencecontrolled synthesis of oligo-and polyrotaxanes is important in the context of the development of both sequence-defined polymers and dynamic functional materials. To date, examples of sequence-controlled rotaxanes are limited to oligorotaxanes on account of the synthetic challenges they pose. This Review sheds light on the pivotal role that sequence isomerism plays in rotaxanes.Synthetic approaches, including orthogonal templation, active-metal templation, self-sorting and snapping, cooperative-capturing, ring-through-ring-shuttling, and molecular pumping, for the construction of sequence-controlled rotaxanes are all discussed in this Review. By comparing the advantages and disadvantages of these different approaches, several possible synthetic strategies are proposed in an attempt to foretell the future of sequence-controlled synthesis of polyrotaxanes.

Sacrificial Mechanical Bond is as Effective as a Sacrificial Covalent Bond in Increasing Cross-Linked Polymer Toughness

“…Our findings suggest that dethreading may contribute to, or even dominate, the impressive toughness of elastomers cross-linked with 3,5-dimethylphenyl-stoppered rotaxanes, which hitherto has not been considered. More broadly, the reported results justify continued effort to identify practical implementations of sacrificial mechanical bonds, and the application niches in which such bonds may offer unique advantages, including in fundamental studies of load relaxation across polymer networks, , mechanochemical feedback loops, and single molecule information storage . For example, our results suggest that the maximum tensile force a rotaxane can withstand without dethreading depends systematically on the steric bulk of the stoppers, potentially enabling the design of rich dynamic behavior resulting from kinetic competition between load relaxation by dethreading and the dissociation of covalent bonds.…”

“…More broadly, the reported results justify continued effort to identify practical implementations of sacrificial mechanical bonds, and the application niches in which such bonds may offer unique advantages, including in fundamental studies of load relaxation across polymer networks, 18,61 mechanochemical feedback loops, 48 and single molecule information storage. 63 For example, our results suggest that the maximum tensile force a rotaxane can withstand without dethreading depends systematically on the steric bulk of the stoppers, potentially enabling the design of rich dynamic behavior resulting from kinetic competition between load relaxation by dethreading and the dissociation of covalent bonds. Such competition has been shown to allow detailed characterization of chain dynamics that is too complex for any alternative method 64 and was previously speculated to enable detailed mechanistic studies and the design of new mechanoresponsive polymers.…”

A Versatile Synthetic Method for Photophysically and Chemically Stable [5]Rotaxane‐Type Fluorescence Dyes of Various Colors by Using a Cooperative Capture Strategy

“…Higher-order rotaxanes consisting of more than two components are generally hard to be synthesized by reason of entropic disadvantage, especially when the interactions are weak between the noncovalently interlocked components. [18][19][20][21] Indeed, previous syntheses of [3]rotaxane-type fluorescence dyes were accompanied by the formation of side products such as [2]rotaxanes lacking PM-𝛼-CD and [3]rotaxanes with different orientations of CDs (Figure 1a). [9][10][11] To solve this trouble for rotaxane-type fluorescence dyes, we planned to employ a cooperative capture strategy developed by Stoddart et al [22] In this strategy, the use of cucurbit [6]uril (CB6) enabled the preferential arrangement of multiple components and alkyne-azide cycloaddition inside CB6 (CB-AAC, CB6-catalyzed alkyne-azide cycloaddition) without Cu(I) catalysts.…”

Sequence Matters: Precise Synthesis of Hetero[3]rotaxane Isomers with Sequence-dependent Chemical Reactivity and Circularly Polarized Luminescence

“…For instance, for hetero [3]rotaxanes with two different wheel components, when the stoppers are different, there will be two sequence isomers 16 . The investigations on the sequence isomerism in heterorotaxanes is of great importance since it would not only enrich the complexity of rotaxanes in both stereochemical and functional aspects 17 but also possibly give rise to interesting motion behaviors such as ring-through-ring shuttling 18 , making them even more attractive for the construction of novel molecular machines for information storage and data processing 19 . However, in previous reports on the synthesis of heterorotaxanes, different wheels were usually introduced through a stepwise manner, which might suffer from some possible limitations such as relatively long synthetic routes, low synthetic efficiencies, and poor structural and functional diversity [20][21][22][23][24] .…”