Mechanical Modulation of Flexible Schiff Base Derivatives with Fluorescence Properties Based on Crystal Engineering

The application of organic molecular crystals is currently limited by their poor mechanical properties. Crystal engineering could be an effective approach to design and modify organic crystals with different structures and diverse mechanical and other properties. In this work, we synthesized a series of N-salicylideneaniline derivatives (Schiff Bases) with different substituents, which exhibited various mechano-responsive behaviors like two-dimensional (2D) elasticity, plasticity, twisting, and fracture. Besides that, distinct fluorescence emission behaviors were observed due to their different crystal structures. Mechanofluorochromic phenomena were demonstrated in flexible crystals where a reversible fluorescence peak shift occurred in elastic crystals and a red shift appeared in plastic crystals. Organic crystals with mechano-sensitive behaviors and fluorescence properties hold great potential in flexible optoelectronic materials, such as sensors and actuators.