Fluorescent bioprobes have been widely utilized in academic research and clinical practice for their unique advantages. However, the scope of the bio-applications of many conventional organic fluorophores is impeded from the self-quenching problem at high solution concentration and in the aggregated state, or the so called aggregation-cause quenching (ACQ) effect. Evidently, ACQ is a harmful photophysical effect in terms of light emission and practical applications. Recently, another emerging photophysical phenomenon associated with chromophore aggregation is aggregation-induced emission (AIE), which is opposite and complementary to the ACQ effect. Archetypal AIEgens are constructed from aromatic phenyl rings, which are hydrophobic in nature. Amphphilic AIEgens, on the contrary,...[ Read more ]

Fluorescent bioprobes have been widely utilized in academic research and clinical practice for their unique advantages. However, the scope of the bio-applications of many conventional organic fluorophores is impeded from the self-quenching problem at high solution concentration and in the aggregated state, or the so called aggregation-cause quenching (ACQ) effect. Evidently, ACQ is a harmful photophysical effect in terms of light emission and practical applications. Recently, another emerging photophysical phenomenon associated with chromophore aggregation is aggregation-induced emission (AIE), which is opposite and complementary to the ACQ effect. Archetypal AIEgens are constructed from aromatic phenyl rings, which are hydrophobic in nature. Amphphilic AIEgens, on the contrary, are seldom designed and prepared.

In this work, several amphiphilic AIEgens are synthesized containing non-ionic, cationic and anionic units. They are soluble in water and form micelles above the critical micelle concentration (CMC). Below the CMC, the AIEgens exist as isolated molecules and emit no light. They, however, emit intensely at above CMC due to the formation of micelle or nanoaggregate. The amphiphilic AIEgens are generally non-toxic and biocompatible.

Nonionic and amphiphilic polyethene glycol-decorated tetraphenylethenes are synthesized by azide-alkyne cycloaddition. Their AIE property, micellation, thermosensitive behaviors and use as fluorescent visualizer for intracellular imaging and tracking are explored. It is found that the AIEgen could tracing the cell growth as long as 5 generations.

Cationic and amphiphilic tetraphenylethene-based pyridinium salts with AIE characteristics for selective cell membrane staining in HeLa cells and bacteria are successfully developed. Owning to the inherent photostability of the AIEgens, the new molecules are excellent AIE cell membrane stains. Interestingly, the molecules can generate reactive oxygen species (ROS) under room light irradiation. The first discovery of ROS generation on AIEgens enables a visible observation of cell necrosis and phototherapeutic effect under mild conditions. This makes them potential as selective phototherapy candidate drugs and it is worthy for further exploration of their phototherapeutic effect in animals.

A novel dual-modal MRI contrasting agent (TPE-2Gd) containing hydrophobic tetraphenylethene unit and hydrophilic diethylenetriaminepentaacetic acid-gadolinium complex was successfully synthesized for both magnetic and fluorescent imaging. Results show that TPE-2Gd is an ideal MRI contrasting agent with long circulation lifetime for diagnosis and short circulation lifetime enough for body clearance.