Enhancement of Mechanophore Activation by Electrostatic Interaction

Mechanophores, which change their chemical structure in response to mechanical stimuli, are widely used to develop mechanoresponsive materials, and their reactivity is greatly affected by the surrounding environment. Here, we focus on the effect of electrostatic interactions on the activation of mechanophores. A series of radical-type mechanophores with ionic functional groups, as well as mixed systems of these radical-type mechanophores with dicarboxylic acid groups and divalent ions were prepared, and their mechano-responsiveness in the bulk was investigated via ball-milling and subsequent electron paramagnetic resonance spectroscopy measurements. The results revealed that the mechano-responsiveness is governed by the introduction of electrostatic interactions into the mechanophores. The effect of electrostatic interactions on the activation of radical-type mechanophores was investigated and their mechano-responsiveness was greatly affected by the ionic species directly connected to the mechanophore and the counter ions or surrounding molecules. A dramatic increase in the reactivity of the mechanophores was achieved by mixing them with metal-containing compounds and a rigid molecule as a comonomer.