THESIS
2020
xxiii, 142 pages : illustrations (some color) ; 30 cm
Abstract
Chirality, as a universal asymmetric feature in our world, exists from the microscopic
single molecules, to mesoscopic assemblies such as DNA and proteins, and finally macroscopic
tissues and our hands. Ever since the discovery of chirality in the 19
th century, the generation
and utilization of chirality are always popular topics due to the desire of exploring the mysteries
of nature. To emphasize the significance of chirality, the Nobel Prize in Chemistry in 2001 was
awarded for asymmetric catalysis. With the development of modern technology, chiral
materials have been exploited into biological, optical, and electronic application fields.
Amongst all the manifestation aspects of chirality, circularly polarized luminescence (CPL)
is one of the most alluring features that convert...[
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Chirality, as a universal asymmetric feature in our world, exists from the microscopic
single molecules, to mesoscopic assemblies such as DNA and proteins, and finally macroscopic
tissues and our hands. Ever since the discovery of chirality in the 19
th century, the generation
and utilization of chirality are always popular topics due to the desire of exploring the mysteries
of nature. To emphasize the significance of chirality, the Nobel Prize in Chemistry in 2001 was
awarded for asymmetric catalysis. With the development of modern technology, chiral
materials have been exploited into biological, optical, and electronic application fields.
Amongst all the manifestation aspects of chirality, circularly polarized luminescence (CPL)
is one of the most alluring features that converts such an invisible characteristic into observable
light emission. As a result, pursuing highly emissive CPL systems has become a general target
of developing novel chiral materials. These obtained CPL-emitting materials have been
successfully applied into biological sensors and display devices. However, conventional
luminogens, including a series of chiral luminogens, often suffer from the phenomenon that
exhibits strong emission in solution state but weakened or even annihilated emission in
aggregate state, which is defined as aggregation-caused quenching (ACQ) effect. This effect
restricts the performance of chiral luminophores in condensed state for application, resulting
in poor CPL performance in practical devices. The creation of AIE luminogens (AIEgens)
could prevent the emitters from ACQ phenomenon due to their opposite photophysical
properties of weak or no emission in solution state but enhanced emission once the aggregates
formed. Combining the merits of AIE and CPL, several projects about constructing novel
emitting materials were carried out in this thesis work.
Firstly, concerning about the mechanism of supramolecular chirality formation, we have
developed a chiral AIEgen undergoing spontaneous hierarchical self-assembly in aggregate
state from vesicles to helical fibers, which can be monitored by in situ and real-time CD spectra.
CPL signals were further induced by co-assembly of the complexes as chiral templates and
achiral luminogens.
Then, inspired by muscular filament sliding in human bodies, muscle-like molecular
motion was found to switch on the CPL emission in a synthesized chiral Au(I) complex. The
pristine powder of both enantiomers was non-emissive, whereas the emission could be
triggered by scratching force. Structural studies revealed no crystal phase change occurred but
only subtle solid-state molecular motion that turned on the CPL emission.
After that, aiming for novel approach to chirality, a simple CPL-emitting device was
fabricated by achiral twisted nematic liquid crystals (TN-LC) doped with achiral AIEgens.
Relatively high-performance CPL emissions from blue to red with luminescence dissymmetry
factor (glum) up to 10
-2 were obtained from those devices without chiral components.
At last, in order to improve the chiral behavior, another chiral AIEgen encountering
aggregation-annihilated circular dichroism (AACD) effect was converted into CPL-emitting
material by doping in liquid crystals (LCs). Additional achiral AIEgens were further added to
the obtained chiral nematic liquid crystal (N*-LC) to gain amplified CPL emission.
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