Mechanochemical Activation of a Bridged-Exciplex Optical Force Probe

Strong demands are placed on optical force probes (OFPs) to detect bond scission on different timescales and in different microenvironments necessitating the development of detection strategies beyond simple on/off reporters. We here introduce OFPs based on bridged-exciplex Diels-Alder adducts. These exhibit fluorescence in both their latent (non-activated) and activated states, distinguishing them from conventional "turn-on" probes. The pronounced solvatochromic character of the latent form additionally enables its use as an environmental polarity sensor, with emission wavelength and intensity responding to the local environment. We incorporate these OFPs into linear chains and polymer networks. Mechanochemical activation is demonstrated both in solution and in the solid state, culminating in spatially resolved imaging of damage zones. Crucially, the activated and latent states differ not only in fluorescence intensity but also in quantum yield and fluorescence lifetime, enabling multimodal contrast. This multi-feature OFP thus represents a promising technology for advanced imaging techniques including high-resolution and lifetime-resolved microscopy methods, substantially expanding the analytical toolkit available for mechanochemistry beyond the limitations of existing OFPs.