A multifunctional AIEgen with high cell-penetrating ability for intracellular fluorescence assays, imaging and drug delivery

Aggregation-induced emission luminogens (AIEgens) with a definite structure-activity relationship play important roles in site-specific bio-imaging and applications. However, the lack of a clear structureactivity relationship for the excited-state intramolecular proton transfer (ESIPT) molecules, which are a series of powerful AIEgens, restricts their biological applications. Herein, the cell-penetrating capability of 4-N, N-dimethylaminoaniline salicylaldehyde Schiff-bases (DSS) with different substituents was investigated. The diethylamino functionalized ESIPT Schiff base (DSS-4-DEA) displayed high cell-penetrating capacity, making this simple AIEgen turn into a more powerful fluorescent functional material in biosystems. The DSS4- DEA was successfully used for a fluorescence assay of the intracellular Cu2+. Besides, the DSS-4-DEA could also be used as an efficient transmembrane carrier to drastically enhance the internalization of DSS-5-Cl to achieve two-color imaging. In addition, the DSS-4-DEA could be used to improve the transportation of anticancer drug curcumin (Cur) into HeLa cells, leading to increased apoptosis. The complete exploration of the structure-activity relationship of ESIPT molecules might supply lots of new applications of AIE materials in biological systems.