Light has always been important to human society, fluorescence is a phenomenon that a molecule emit longer wavelength of light under photoexcitation. Fluorescent materials are widely used in detection of chemicals or biomolecules. However, surrounding environment in most of the biosystem are aqueous, while most of the fluorescent materials are hydrophobic which makes them aggregate in biosystem. Most of the conventional fluorescent materials consist of π-conjugation system, which suffer from a phenomenon named aggregation caused quenching (ACQ). Therefore, it limits the use of fluorescent materials in biological field. By further research, some molecules with π-conjugation system and rotatable bonds are found to be emissive in aggregated state and the phenomenon was named as aggregation...[ Read more ]

Light has always been important to human society, fluorescence is a phenomenon that a molecule emit longer wavelength of light under photoexcitation. Fluorescent materials are widely used in detection of chemicals or biomolecules. However, surrounding environment in most of the biosystem are aqueous, while most of the fluorescent materials are hydrophobic which makes them aggregate in biosystem. Most of the conventional fluorescent materials consist of π-conjugation system, which suffer from a phenomenon named aggregation caused quenching (ACQ). Therefore, it limits the use of fluorescent materials in biological field. By further research, some molecules with π-conjugation system and rotatable bonds are found to be emissive in aggregated state and the phenomenon was named as aggregation induced emission (AIE). However, those molecules showing AIE still consist of aromatic rings, which increased their cytotoxicity. Later, some natural non-conjugated polymer such as cellulose and starch are found to be emissive in visible region under ultra-violet light. They do not have conventional fluorophore, instead, they have electron rich heteroatoms such as oxygen. These non-conjugated fluorescent molecules are named as clusteroluminnogens and they exhibit clusterization-induced emission. In this thesis, the photophysical properties of polyethylene glycol (PEG), maleimide (MI) and succinimide (SI) and their derivatives are under investigation. All of them are found to be emissive when their molecules start to cluster. The interaction between oxygen atoms or sulphur atoms in cluster are found to be responsible for the emission. Clusteroluminogens are non-conjugated molecules and their structure diversity is much greater than conventional fluorescent materials, which allow them to be used in imaging of biomolecules in biosystem and detection of various chemicals.