Tunable Mechanoresponsive Self-Assembly of an Amide-Linked Dyad with Dual Sensitivity of Photochromism and Mechanochromism

Photo- and mechanoluminescent materials that exhibit tunable emission properties when subjected to external stimuli have a wide variety of applications. However, most mechanoresponsive materials have a mechano-induced structural transition from crystalline to amorphous phase, and there are only few reports on the crystalline to crystalline transformation. This study reports an amide-linked dyad P1 containing spiropyran and naphthalimide chromophores with dual sensitivity of photochromism and mechanochromism. Under light and mechanical stimuli, P1 performs different color transition. With mechanical force, the morphologies of P1 change from microfiber to nanosphere and the amide group in P1 plays a vital role in these transition processes. Mechanical force can induce the morphology change of P1 through enhancing pi-pi stacking and destroying hydrogen bonds. These results demonstrate the feasibility of the design strategy for new mechanoresponsive switching materials: both pi-pi stacking and hydrogen bonding of the dyad contribute the mechano-induced crystalline/crystalline transformation.