ACQ/AIE transition of rofecoxib-based analogues via combined ring expansion and amino dimethylation strategies and their multiple stimuli-responsive fluorescent behaviors

Abstract

In this work, two innovative molecular design philosophies have been successfully developed to achieve the fluorescence conversion of 4 targets from aggregation-caused quenching (ACQ) to aggregation-induced emission (AIE). First, this conversion was achieved by employing a ring expansion strategy, where the pyrrolidinyl group of F0 was replaced with a piperidyl group, resulting in the target molecule FA. Next, by dimethylating the amino group of F0, the resulting compound FB also exhibited AIE properties. Moreover, when these two strategies were combined, the corresponding compound FAB exhibited the most obvious AIE properties with the highest quantity yield in the solid state (Φ_PL,solid = 17.72%). The fluorescent behaviors of these three compounds in different states were elucidated clearly by analyzing their single X-ray crystal and theoretical calculation data. In addition, their potential multi-functional applications were investigated in mechano-sensors, trace water sensors and lipid droplet (LD) imaging. Conclusively, this work not only presents a better understanding of structure–fluorescence property relationship, but also offers two new strategies for developing new promising AIEgens.