New stimuli-responsive aggregation-induced emission systems : development, mechanisms and applications

Abstract

Stimuli-responsive luminescent materials are attracting tremendous attention for their potential applications in optical sensors, bioimaging, data recording, molecular switch and so on. To achieve a stimuli-responsive luminescent material, which must respond to at least one of the following external stimuli, including light, heat, mechanical force, vapors, pH value, or magnetic field, in an observable way. Some of them even operate in a multi-stimuli-responsive mode, showing multi-color emission behaviors. Usually, they rely heavily on aromatic compounds with intro/intermolecular interactions and the resulting variation of interactions, such as large π...π interactions, dipole⸳⸳⸳dipole interactions, D-A interactions, or hydrophobic effect. These weak forces may allow the transformation of aggregation modes or self-assembly architectures, leading to a remarkable emission behavior change. Thus, stimuli-response behaviors could also be as strong tools to verify the emission mechanism by constructing the structure-property relationship of the corresponding luminescence changes. This thesis mainly focused on the development of stimuli-responsive materials and discovered the mechanism behind the phenomena as well as some new linking strategies in biology. Firstly, linear gold(I) complex TPPGPA with conglobate trimer configuration trigged by aurophilic interactions in the crystalline state was prepared to emit dual phosphorescent white-light emission, which exhibited multi-stimuli responsive luminescent properties including thermochromism and mechanochromism. Moreover, the molecular packing mode and aurophilic interactions regulation were subtly taken as a functional relationship of the experimental correlation with emission. Interestingly, to simply mix the precursor with TPPGPA with a ratio of 1:1, we could achieve cocrystal with distinct packing. The emission color changes upon grinding and hydrostatic pressure were also evaluated. Next, we developed a simple approach to achieve organic luminescent radical ions, which show strong solid-state emission and superior stability with reversible light-stimuli response property. Mechanism study reveals that the molecular symmetry breaking in the crystalline state caused molecular conformation and redox property change, as well as the unique molecular packing, facilitate the light-stimuli radical generation. At last, we provide a strategy for metal-free click bioconjugation at diverse levels based on activated alkynes. This work, even though not very match with the theme of the stimuliresponse materials but is very meaningful. As a proof-of-concept, the abundant native groups, including amine, thiol, and hydroxyl groups, can directly react with activated alkynes without modification in the absence of metal catalysis. Through this strategy, high-efficient modification and potential functionalization can be achieved for natural polysaccharide, biocompatible polyethylene glycol (PEG), synthetic polymers, cell-penetrating peptide, protein, fast whole-cell mapping, and even quick differentiation and staining of Gram-positive bacteria, etc. Therefore, the current metal-free click bioconjugation strategy based on activated alkynes is promising for the development of quick fluorescence labeling and functional modification of many targets and can be widely applied towards the fabrication of complex biomaterials and future in vivo labeling and detection.

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Benzhong TANG (Supervisor)