Light is of essential importance to the humankind. It is one the most fundamental and indispensable elements to our life and society. Research on fluorescent materials remains a principal focus and hot topic in the scientific community because of their vast potential applications. Numerous fluorophores have been prepared and found to be highly emissive in their dilute solutions. However, for most practical applications, they are used as solid films and aggregates. Unfortunately, the emission of many conventional fluorophores is partially or completely quenched upon aggregate formation. Such a phenomenon of aggregation-caused quenching (ACQ) has been documented for more than half a century since Förster’s discovery in 1954. Although ACQ fluorophores have found many useful applica...[ Read more ]

Light is of essential importance to the humankind. It is one the most fundamental and indispensable elements to our life and society. Research on fluorescent materials remains a principal focus and hot topic in the scientific community because of their vast potential applications. Numerous fluorophores have been prepared and found to be highly emissive in their dilute solutions. However, for most practical applications, they are used as solid films and aggregates. Unfortunately, the emission of many conventional fluorophores is partially or completely quenched upon aggregate formation. Such a phenomenon of aggregation-caused quenching (ACQ) has been documented for more than half a century since Förster’s discovery in 1954. Although ACQ fluorophores have found many useful applications, realization of their full potential has become impossible. In our search for efficient luminescent materials, we observed a phenomenon of aggregation-induced emission (AIE) in a group of propeller-shaped molecules such as siloles and tetraphenylethene. These AIE luminogens (AIEgens) show weak or no fluorescence in the solution state but emit efficiently when aggregated. Through systematic studies and mechanistic analyses on these molecular rotors, we have deduced the restriction of intramolecular motion (RIM) is the main cause for their AIE effect. Since the observation of the AIE phenomenon in 2001, excellent work has been done to uncover its underlying mechanism and realize its practical uses. However, much remains to be explored in this young research area. The AIE effect can be utilized in many applications wherever RIM process is activated, with possibilities limited by only our imagination. Our group has reported many different applications like optic devices, chemosensors, bioprobes, bio-imaging and etc. AIEgens always enjoyed highly brightness, specificity, biocompatibility and photostability. Although AIEgens demonstrated many advantages in bio-applications, AIEgens with long-wavelength absorption and emission were still rarely reported. In this research project, we have designed different red-emissive AIEgens and utilized their potential in bio-applications. In Chapter II to IV, we developed a dual-targeting AIEgen to nucleolus and mitochondria, and two plasma-membrane-targeting AIEgens for monitoring morphology changes of the membrane and generating ROS for PDT respectively. Another AIEgen was able to generate ROS for increasing radiosensitivity of cancer cells in radiotherapy (Chapter V) and a water-soluble AIEgen was functionalized for antibody labelling through receptor-mediated endocytosis (Chapter VI). In Chapter VII, a photoactivatable AIEgen was demonstrated as a model for super-resolution imaging.