Conventional organic fluorescent materials mostly take coplanar conformation, and thus suffer from fluorescence quenching in the aggregate state or at high concentration due to the strong intermolecular π-π interaction, which leads to the formation of excimer or exciplex and decays the exciton energy nonradioatively. Fluorescent materials with aggregation-induced emission (AIE) characteristics show exactly opposite behaviors. They are non-emissive when molecules present in solution but fluoresce intensely as aggregates. In general, AIE effect arises from restriction of intramolecular motion (RIM), which includes restriction of intramolecular rotation (RIR) and restriction of intramolecular vibration (RIV). This discovery brings a new concept in molecular design that perfectly sol...[ Read more ]

Conventional organic fluorescent materials mostly take coplanar conformation, and thus suffer from fluorescence quenching in the aggregate state or at high concentration due to the strong intermolecular π-π interaction, which leads to the formation of excimer or exciplex and decays the exciton energy nonradioatively. Fluorescent materials with aggregation-induced emission (AIE) characteristics show exactly opposite behaviors. They are non-emissive when molecules present in solution but fluoresce intensely as aggregates. In general, AIE effect arises from restriction of intramolecular motion (RIM), which includes restriction of intramolecular rotation (RIR) and restriction of intramolecular vibration (RIV). This discovery brings a new concept in molecular design that perfectly solve the detrimental ACQ problems and further encourage technological innovation in the application field of fluorescence.

Making good use of RIM processes, countless advanced optoelectronic applications of AIEgens can be developed. Other than utilizations of AIEgens in chemical fields, the possibility of utilizing AIEgens in biological applications has also been explored. AIEgens are highly luminescent, photostable and biocompatible, and are thus promising for various biological applications. Attracted by the superior performance of AIEgens as novel luminescent materials, in this thesis, I launched a program to develop novel AIEgen systems and explore their technological applications in biochemical fields. Specifically, I developed and synthesied a novel boron-based AIEgen and demonstrated its applications in enantiomer discrimination and morphology visualization of polymer blends. Besides, two diaminomaleonitrile-based Schiff bases with a donor–acceptor structure and an aggregation-enhanced emission feature were sythesized and its mechanochromic properties and applications in bioimaging were reported. Then, I started focusing on biological applications of the AIEgens. I noticed the importance of detection and monitoring of cell apoptosis. Thus, a novel AIE-based bioprobe was synthesis for detection of cell apoptosis as well as differentiation of early and late stages of cell apoptosis mediated by H₂O₂. Besides, I also utilized a AIEgen for specific imaging of lipid droplets. Other than exploration of biological applications of AIEgens in cell systems, I also designed a novel AIEgen with red emission color and exploited it to image bacteria. I also noticed that this AIEgen can sensitize the generation of ROS upon photoexcitation, and applied it to wash-free imaging and killing of bacteria.