Modulating the Reactivity of Force-Sensitive Molecules

Precisely modulating the reactivity of force-sensitive molecules—or mechanophores—could be useful for tuning the properties of functional materials, such as force-responsive polymers. However, current modulation strategies rely heavily on meticulously designing or significantly changing the actual mechanophore structure, a process that is often challenging, time-consuming, and typically requires reconstructing the molecules from scratch.

Hai Qian, Fudan University, Shanghai, China, and colleagues have developed a new “pulling strategy” to modulate the reactivity of a mechanophore, specifically an anthracene-maleimide adduct, by introducing a ring-shaped unit. In a “traditional” linear structure (pictured above on the left), long chains are attached to the mechanophore at a single point each. In the team’s modified cyclic structure (pictured above on the right), a ring-like structure is attached to two different atoms that are located on opposing sides of the anthracene’s central ring.

The researchers found that this new pulling strategy leads to a significant suppression of the mechanophore’s reactivity and activation efficiency, reducing them by approximately 92 % and 88 %, respectively, without needing extensive structural modifications.

To show that this strategy can also be used in multi-mechanophore systems, the team combined either a linear anthracene-maleimide mechanophore (pictured below in the first row) or a “cyclic” one (pictured below in the second row) with a spiropyran mechanophore, achieving hierarchical mechanochromism.

The resulting tandem systems provide different optical outputs because a different mechanophore is activated first: The anthracene-maleimide unit is broken first in the “linear” variant (pictured in blue), while the spiropyran is “pulled apart” and activated first in the system using the cyclic pull structure on the anthracene-maleimide adduct (pictured in purple). Overall, the work provides new possibilities for the development of advanced functional materials with complex responses to mechanical force.