Polymer Mechanochemistry of Component Parts for Artificial Molecular Machines

Abstract

A huge variety of synthetic molecular machines and their components are developed, and their actuation at the molecular level is demonstrated and used in microscopic molecular systems and macroscopic materials. Not only the actuation but also their mechanical responses are critical to the applications. In other words, a molecular machine or a machine part insensitive to mechanical forces can produce mechanical work by another external stimulus even under mechanical loading as an actuator, whereas that sensitive to mechanical forces can be controlled to generate motions by mechanical forces as a mechanophore. To explore the mechanical response empirically, a molecular machine or a part of it has to be chemically incorporated in a polymer chain, through which elongational forces can be applied to the embedded molecule. Here we review the mechanochemistry of component parts for artificial molecular machines represented by photoswitches and mechanically interlocked architectures using polymer mechanochemistry.This article is protected by copyright. All rights reserved

Molecular Probing of the Microscopic Pressure at Contact Interfaces

“…Fluorescence techniques allowing to directly probe local forces using mechanochromism are widely applied in the studies of polymer systems . Color changes under the influence of force can originate from several physical effects, ranging from changes in intermolecular interactions in crystals and aggregates to bond breaking (mechanochemistry) − and more gradual conformational changes that affect molecular color. Notably, most of these studies examine the tension stresses in bulk, typically by chemically cross-linking the probe within the bulk material.…”

Foldamer-Based Mechanoresponsive Materials: Molecular Nanoarchitectonics to Advanced Functions

“…In the pursuit of such biomimetic functions, recently synthetic chemists have developed materials that show response to the mechanical force, often referred to as mechanoresponsive materials and a subclass of these systems that show force-induced optical changes is termed mechanochromic materials. − The preparation of such materials and investigation of their properties have been of increasing interest in the last decades owing to their sophisticated functions, such as strengthening of mechanical properties, change of optical behavior, and the emergence of chemiluminescence. − To achieve such material, a mechanoresponsive unit can be integrated into polymer networks to have a broader scope of their utility. Over the past few years, a large variety of synthetic small molecules have been used as mechanoresponsive units. ,,− While the introduction of some of these units in polymer resists any kind of mechanical deformation, the other majority exhibit mechanochromic behavior through irreversible covalent bond rupture beyond a certain threshold, thus, limiting their practical utility. Since activation of their mechanochromic behavior relies on the rupture of one or more covalent bonds, this method is typically energy-demanding.…”