Impact of a Mechanical Bond on the Activation of a Mechanophore

Abstract

Mechanical bonds are known to efficiently absorb mechanical energy at low forces, but their behavior at high forces is unknown. Here we investigate the impact of a mechanical bond on the rate of activation of a Diels–Alder mechanophore. Using a combination of experimental and computational techniques, we found that the rate of a retro-Diels–Alder reaction under tension is decreased when the mechanophore is embedded in the axle of a rotaxane due to the presence of a competing high-stress region at the junction between the macrocycle and the axle.

Mechanical activation of polymers containing two adjacent mechanophores

“…another bond being significantly elongated) where the axle is deformed by the macrocycle. 5 Based on this latter observation, we hypothesised that two mechanophores in close proximity should affect each other's mechanical activation due to the presence of two competing elongating bonds. Here we investigate the mechanical activation of polymers containing two adjacent Diels-Alder (DA) adduct mechanophores 12 in various geometries.…”

“…1,2 This process is usually achieved by one of two polymer architectures: a chain-centred system, whereby a single mechanophore is embedded in the centre of a polymer chain 3 (Figure 1a), or a multi-mechanophore system, where the entire polymer consists of mechanophores linked together (Figure 1b). 4 These architectures have been used to uncover the impact of the linker structure, [5][6][7][8][9][10] which can be used to manipulate the mechanochemical coupling, and the mechanophore geometry, [11][12][13][14][15][16][17][18][19] where the connectivity with th actuating polymer dramatically impact the mechanochemical coupling, on the mechanical activity of a mechanophore. However, little is known on how the presence of a mechanophore affects the activation of an adjacent mechanophore.…”

“…However, little is known on how the presence of a mechanophore affects the activation of an adjacent mechanophore. 20 During our investigation of the mechanochemistry of the mechanical bond, 5,[21][22][23] we have found that a mechanophore could be protected from mechanical force when embedded in the ring of a catenane, 23 and that the use of a rotaxane as a force actuator can slow the activation of a mechanophore embedded in its axle by creating a competing high-stress region (i.e. another bond being significantly elongated) where the axle is deformed by the macrocycle.…”

The Rise and Promise of Molecular Nanotopology

“…Upon application of mechanical forces, the component rings within the[2]catenane can circumrotate with respect to each other until the tension equalizes over the entirety of the catenated framework. This relative motion diverts mechanical forces effectively away from the intracyclic D-A cycloadduct, reducing its mechanical susceptibility.Although rotaxanes230 have also been reported to affect the responsiveness ofPage 26 of 79 CCS Chemistry 27 mechanophores, the topologically trivial structures themselves are susceptible to forceinduced degradation. In contrast, catenanes are free of this weakness, rendering them more practical to tame the activity of mechanophores without impairing the mechanical integrity of the polymer chains.…”

Mechanical Force Induces Ylide‐Free Cycloaddition of Nonscissible Aziridines

“…These polymers have found several applications, including in structure engineering, [2] catalysis, [3] sensors, [2a] patterning, [4] recycling of resources, [5] materials transfer, [6] and gating to regulate other reactions. [7] Such systems can activate covalent and coordination bonds, [2a-f, 3, 5, 6b, 7, 8] and change the electrical and optical properties of polymers. [2a, 4, 9] The activation of mechanophores also allows one to steer chemical reactions toward routes that are inaccessible under traditional thermal and photochemical conditions.…”