A novel insight into the dual state emission mechanism of a new rofecoxib derivative and its multi-functional applications

There is growing interest in developing dual-state emission luminogens (DSEgens) in the fluorescent materials community due to their bright emission in both dilute solution and the solid state and potential applications in various areas. In this work, we have developed a new dual-state emission (DSE) luminogen by integrating a benzothiazolium unit into the rofecoxib skeleton, namely 5-((Z)-4-(((E)-3-methylbenzo[d]thiazol-2(3H)-yli- dene)-amino)benzylidene)-rofecoxib (p-RBZ). Importantly, by combining theoretical calculations and experimental investigation, a novel insight into the DSE mechanism of p-RBZ is firstly proposed. The reduced density gradient (RDG) calculation and single X-ray data analysis, both revealed that p-RBZ had strong intra-molecular pi-pi interaction between a ring and d ring, which can limit molecular rotation, reduce the rate of non-radiative transition, and enhance luminous efficiency in solution. Meanwhile, the conformation twist of p-RBZ and the highly restricted intermolecular pi-pi stacking may permit their bright emission in the solid state from the single-crystal X-ray and Hirshfeld surface analysis. Furthermore, p-RBZ displayed apparent solvatochromism, mechanochromism, and lipid droplets-specific imaging properties. These results implied that DSE-active p-RBZ had the potential to be developed as a mechanical-force sensor and lipid droplets imaging probe.