Mechanochemical Activation of Fluorogenic CuAAC "Click" Reactions for Stress-Sensing Applications

Abstract

Strategies for visualizing stress within polymeric materials are of growing interest during the past decade. In this paper, stress-sensing materials, triggered by a mechanoresponsive catalytic system based on latent copper(I)bis(N-heterocyclic carbene) mechanophores, are reported, which can be activated by compression force to trigger a fluorogenic copper(I)-catalyzed alkyne/azide "click" cycloaddition reaction, activating a fluorescent dye useful for stress-sensing applications in bulk polymeric materials. The focus is placed on the polymeric architecture, which is responsible for an efficient stress transmission, revealing the greatest activation for network-based mechanocatalysts, observing "click" conversions up to 44%, while chain-extended and linear mechanocatalysts activate either in a less efficient manner or are not completely latent in the initial state. The developed catalysts enable "irreversible" mechanochromic systems for stress-sensing devices.

Keywords: click reactions; mechanocatalysts; mechanochemistry; mechanophores; stress-sensing.