Exploration of rational donor–acceptor adjustment strategies to achieve ACQ to AIE transformation and their potential applications as multi-functional AIEgens†

In this work, a new series of rofecoxib analogues were designed and synthesized by employing the migration of the donor (D) group and donor (D)–acceptor (A) switching principle to achieve ACQ–AIE conversion. Among them, when the D unit dimethylamino was anchored on the para-position of the benzene ring D, the corresponding compound L1, namely (Z)-5-(4-(dimethylamino)benzylidene)-4-(4-(methylsulfonyl)phenyl)-3-phenylfuran-2(5H)-one, was obtained exhibiting obvious aggregation-caused quenching (ACQ) behavior. Subsequently, after migrating the D group from ring D to ring B, the resulting L2 exhibits an aggregation-induced emission (AIE) effect. Meanwhile, by switching the position of the D and A units based on the structure of L1, the corresponding compound L3 also shows AIE behavior. These results demonstrate that migrating the position of the donor group and switching the positions of the donor and acceptor have significant effects on the fluorescent properties of the compounds. Moreover, single crystal X-ray analysis of L2 and L3 revealed that the stronger molecular C–H⋯π interactions contribute to greater structural rigidification, which in turn enhances their bright emission in the solid state. In addition, L2 and L3 exhibited solvatochromic, acidichromic, and trace water properties with reversible multi-stimulus behaviors. More importantly, L2 and L3 demonstrated highly specific fluorescent imaging ability (R_L2 = 0.97, R_L3 = 0.98) toward lipid droplets in living MCF-7 cells, with low cytotoxicity. In summary, the creative design concepts of adjusting the position of D and switching the positions of D and A units, as well as the ACQ to AIE conversion provide alternative ways for developing new multifunctional AIEgens, L2 and L3.