A cyclic cinnamate dimer mechanophore for multimodal stress responsive and mechanically adaptable polymeric materials

Smart molecules that undergo orthogonal chemical transformations in response to force and other stimuli are highly attractive in materials science. Such moieties, when incorporated into polymer chains, allow fine tuning of material responses including mechanical properties to mechanical loads. Here we show that the unique mechanochemical and photochemical properties of the methanone tethered cinnamate dimer (MTCD) make it a promising candidate to achieve multimodal stress-responsive and mechanically adaptable polymeric materials. Stretching a polymer of the MTCD results in a force induced retro [2 + 2] cycloaddition and produces methanone-biscinnamate (MBC) moieties. This mechanochemical reaction simultaneously increases the fluorescence and releases a stored length of >6 A per MTCD, suggesting its potential in damage indication and material toughening. Moreover, on-demand strengthening/healing of the pristine and/or the mechanically degraded polymers can be achieved by the photochemical reaction of the MTCD and/or [2 + 2] cycloaddition of the mechanically generated MBC and this feature is orthogonal to the mechanochemical reaction of the MTCD.