THESIS
2014
iv leaves, v-xxxiii, 196 pages : illustrations (some color) ; 30 cm
Abstract
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,...[
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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.
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