One-step facile transformation from rofecoxib to reversible mechanofluorochromic materials with dual-state emission

Over the past decade, dual-state emission (DSE) materials have attracted attention due to their ability to emit in both states and their potential application in various areas. Therefore, exploring a highly efficient strategy to develop DSE materials has become a hot research topic but remains a challenge. Herein, we have successfully designed and synthesized a couple of rofecoxib analogues 5-(2-tert-butyl carbamate)-benzylidene-rofecoxib and 5-(4-tert-butyl carbamate)-benzylidene-rofecoxib (NOR1 and NOR2) using a one-step reaction, and both of them exhibit DSE properties and NOR1 shows reversible mechanofluorochromism properties under external multiple stimuli. The fluorescence variations of NOR1 were interpreted via analyzing density functional theory (DFT) information, and powder X-ray diffraction (PXRD) and differential scanning calorimetric (DSC) data. Furthermore, single crystal X-ray analysis of NOR2 revealed that the highly twisted molecular conformation is responsible for its emission in the solid state and p-p stacking might be the main reason for it poor mechanofluorochromic effect. Subsequently, the potential applications of NOR1 were also investigated in the areas of anti-counterfeiting and self-erasable secure writing platforms. In biological experiments, NOR1 could image lipid droplets (LDs) in living HeLa cells and emit green fluorescence with an increased value of signal to noise (S/N) ratio compared with that of Nile Red.