Mechanophores are functional molecular units that exhibit selective chemical responses to mechanical perturbations. The outcome involves various forms: color changes, fluorescence, chemi-luminescence, activation of latent catalyst, and generation of reactive species such as free radicals, acids, and small organic molecules. Polymeric materials embedded with mechanophores have demonstrated a variety of stress-responsive properties including stress sensing, damage reporting, remote light generation, and self-healing. Among these applications, releasing small molecules from polymer backbone is one of the most challenging tasks. In order to transduce the mechanical force experienced by the polymer matrix to the mechanophores, usually two opposite end groups of the mechanophores are attached to the polymer backbone. Therefore, after mechanophore activation the residual moieties remain bonded to the polymer backbone with no molecule released. So far, small-molecule releasing is based on two general approaches: (1) Activating a rearrangement reaction that release molecules; and (2) molecular fragmentation. Due to the nature of most rearrangement reactions, the former approach is usually limited to releasing simple species (e.g. HCl). The latter fragmentation approach is an example of releasing more complex molecules; however, it generally requires specialized molecular design with limited varieties, and also demands significantly higher mechanical stress for the activation. Herein, we report a new platform for mechanophore design with molecule-releasing capability by introducing the concept of mechanically interlocked molecular machines. In a rotaxane molecular machine, tasks are accomplished by controlling the movement of the wheel along the axle. Therefore, we hypothesize that by guiding the directional sliding of the wheel along the axle, mechanical forces are applied to mechanophores viatopological hindrance, allowing for activation of mechanophores on the axle and “extrude out” the generated small molecules. This new concept of mechanophore activation generalizes the use of a variety of mechanophores and opens a pathway towards single-end functionalized mechanophores.

Mechanophore activated by a rotaxane molecular machine

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.