A turn-on mechanochromic luminescent material serving as pressure sensor and rewritable optical data storage

Mechanochromic luminescent (ML) materials can be roughly classified into two categories: turn-off type and turn-on type. Clearly the latter is more reliable because it has higher sensitivity and lower false-positive signals or background noises. Herein, a turn-on type ML material, (E)-4-((2-hydroxy-5-methylbenzylidene)amino)-3-methylbenzoic acid (MMA), is presented, which is designed by integrating appropriate electron donor-acceptor (D-A) moieties into a twisted conjugation core. MMA displays both aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) properties. In addition, it glows weakly but exhibits notable emission enhancement under mechanical stimuli, and the two emission states can be repeatedly switched by grinding-fumigation treatment. Unlike the ML materials based on crystalline-amorphous phase transition, the ML of MMA is ascribed to the coupling and decoupling of the D-A units, regardless of the phase state. And this new working mechanism is confirmed by crystallographic data and DFT calculations. A pressure sensor based on MMA was fabricated, affording a low detection limit down to 21.6 Mpa. MMA further facilitates the fabrication of a ML recording medium, which allows for piezo-writing and fumigation-erasing of data, demonstrating a reliable prototype of optical data storage.