AIEgens for dual second harmonic generation and fluorescence “turn-on” imaging of membrane and photodynamic therapy in cancer cells

Abstract

The integration of second harmonic generation (SHG) microscopic imaging and aggregation-induced emission fluorescence imaging would greatly boost the imaging outcomes because of the combination of merits in each imaging modality. Although the customized molecular design of probes is crucial to realizing this purpose, it has rarely been reported so far. Herein, the design and synthesis of dyes with both SHG efficiencies and aggregation-induced “turn-on” of fluorescence signals are reported for wash-free imaging to reveal their kinetics in the cells. The probes are constructed using a 4-(2,2-bis(4-(diethylamino)phenyl)vinyl)-1-alkyl-pyridine-iodide core with torsional, noncentrosymmetric, conjugated donor–acceptor structures, and alkyl chains of different lengths (referred as EAPV2, EAPV6, and EAPV12). The probes aggregate in cell membranes and offer a tight noncentrosysmetric microenvironment to restrict their molecular motion, leading to the turn-on of fluorescence imaging with a high signal-to-background ratio. At the same time, the noncentrosymmetric structures of the probes turn on real-time SHG signals/imaging revealing detailed kinetics during membrane-probe interactions. The SHG and fluorescence dual probing reveals the best membrane targeting capability of EAPV12, which has the longest alkane chain. In addition, EAPV12 was tested and showed high photodynamic therapeutic efficacy in cancer cell ablation. This research demonstrated that dual SHG and aggregation-induced emission (AIE) probes may be used to reveal detailed kinetics of molecules on the membrane and help the design and selection of functional materials.