ACQ-to-AIE conversion by regio-isomerization of rofecoxib analogues for developing new multi-functional aggregation-induced emission luminogens

The development of aggregation induced emission luminogens (AIEgens) has attracted increasing attention in recent years as the potential of their application in various areas, including data storage and bioimaging has been realised. However, most of the AIEgens have large conjugation systems which were obtained via lengthy synthetic processes. Herein, we have successfully developed a new pair of far-red fluorescent molecules (λmax = 652 nm, 688 nm), ROF1 and ROF2, which were designed and derivatized from rofecoxib by one-step reaction. Specifically, ROF1 with a para-piperidine shows a classical aggregation caused quenching (ACQ) effect. In contrast, by shifting the piperidine group from para-to ortho-position, the ROF2 exhibits typical AIE behavior. Based on the analyses of single-crystal X-ray data, the AIE property of ROF2 could be ascribed to the highly twisted molecular conformation and loose packing modes caused by the ortho-position of piperidine. These findings allow us to have a better understanding of the impact of the substituent position on the AIE properties. Moreover, the fluorescence of ROF2 was sensitive to multi-stimulus, such as grinding, immersing (solvating), heating and altering pH value, which enabled its potential application in data storage, security ink and pH sensing. In biological experiments, ROF2 could selectively image lipid droplets (LDs) in living HeLa cells. In summary, the regio-isomerization effect used in this article successfully developed a promising AIEgen, ROF2, and provided a principle for the design of new AIEgens.