Controlling Mechanically Induced Luminescence in Polycaprolactone via Precision Circular Mechanophore Size Design

Recent advances in mechanophores have enabled novel strategies for designing pressure-sensitive devices and force-responsive materials. In particular, mechanophores based on a molecular ring have garnered significant attention for their high reversibility and low activation energy. However, the impact of conformational changes of these mechanophores within polymer networks on the material’s mechanosensitivity remains poorly understood. We designed two fluorescent macrocycles with distinct sizes and integrated them into polycaprolactone (PCL) cross-linked networks, enabling systematic investigation of how macrocycle dimensions govern the materials’ mechanochromic response. We find that PCL networks with fluorescence macrocycles of distinct sizes exhibited different strain-dependent fluorescence quenching and that this response remained highly reversible across multiple cycles. Furthermore, introducing smaller macrocycles increased polymer chain rigidity, resulting in significantly longer fluorescence lifetimes in the fabricated samples. This work demonstrates that tuning the size of mechanochromic macrocycles can optimize the force-optical response of materials, providing a new strategy for designing highly sensitive mechanochromic systems.