Design, Synthesis, And Application Of POSS-Containing Fluorescent Polymers

Polyhedral oligomeric silsesquioxane (POSS) is regarded as a special family of organic-inorganic hybrid materials at a molecular level. It can be readily incorporated into virtually any existing polymer system through either grafting or polymerization after the functionalization of pendant arms. Research into POSS-containing polymers has intensified during the past decades, revealing dramatic improved properties well suited for various applications. Recently, a great deal of interest has been focused on the applications of POSS in organic semiconductors. It has been demonstrated that the incorporation of POSS onto organic semiconductors has potential for the enhancement of properties such as thermal and thermomechanical stabilities, mechanical toughness, optical transparency, and solubility. Even more importantly, the unique nanoscale cage-shaped structure of POSS can improve the luminescence in condensed states by suppressing the concentration quenching caused by intermolecular interactions. From this viewpoint, POSS is attractive as a nanobuilding block in highly fluorescent polymers. As far as we know, however, not much effort has been devoted to developing POSS-containing fluorescent polymers except POSS functionalized conjugated polymers for application in organic light emitting diode. In this thesis, we have designed and synthesized three new types of POSS-containing fluorescent polymers, including POSS-containing conjugated coordination polymers, POSS-containing fluorescent amphiphilic polymers, and POSS-containing polymer degree-dependent fluorescent polymers. Besides, preliminary studies on the application of these POSS-containing fluorescent polymers were also involved. This dissertation includes the following four parts:1. A new kind of POSS grafted bis(8-hydroxyquinoline) zinc-based conjugated coordination polymer was designed and synthesized. The experimental results suggested that incorporation of POSS moieties not only effectively improves the solubility and inoxidizability of the bis(8-hydroxyquinoline) coordination polymers, but also prevents the fluorescence quenching effect caused by intermolecular aggregation. As a soluble solid state fluorescent material with a quantum yield of0.26, the newly prepared polymer can be fabricated into green fluorescent nanoparticles through self-assembly in chloroform. Thus we have demonstrated a facile approach for design and preparation of soluble conjugated metal coordination polymers as advanced materials.2. A novel amphiphilic polymer possessing a perylene bisimide (PBI) bridge between a POSS moiety and a PNFPAM chain was designed and synthesized. The target polymers were efficiently synthesized by atom transfer radical polymerization with controlled molecular weight and low polydispersity, as characterized by1H NMR spectroscopy and GPC. Hybrid nanoparticles (NPs) were then fabricated via the self-assembly of the polymers in aqueous solution. Due to the incorporation of POSS moieties, the hybrid NPs retain the luminescence in its aggregate state and show red emission with the fluorescence peak at645nm and a quantum yield of0.27. Moreover, based on the thermoresponsive PNIPAM coronas, the fluorescence quantum yield of the self-assembled hybrid NPs can be further improved to be0.43by changing temperature. The research not only developed the application of POSS to PBI derivatives but also provided a new strategy for design and preparation of red fluorescent NPs with environmental responsiveness.3. A polymeric NP-type sensor with high selectivity and sensitivity for rapid detection of fluoride ion in aqueous solution based on the specific reaction between fluoride ions and POSS has been developed. The NP design involves the assembly of a PBI-bridged POSS-containing amphiphilic polymer structure with POSS-based cores. A fluoride ions sensing process can partially or completely hydrolyze POSS nanocages to induce the aggregate of PBI dyes in NP cores and quench the intense red fluorescence. Compared with conventional chemosensors, the NP-type sensor exhibits rapid response even in pure water because the NP core provides a local highly hydrophobic environment as well as enriched fluoride ion binding sites (Si-O bonds) for the detection. The facile synthetic accessibility and biocompatible composition of the NP-type sensor makes it convenient and attractive for practical detection of fluoride ions in drinking water and biological system.4. A novel methacrylate-type monomer based on POSS substituted PBI has been designed and synthesized. The molecular structure of the monomer was confirmed by NMR spectra. Various polymers with different molecular weight were prepared through reversible addition-fragmentation chain transfer polymerization. It was found that the fluorescent properties of the obtained polymers were dependent on the degree of polymer. Upon the increase of polymer degree, the fluorescent color for solutions of the polymers changed from green to red, accompanied by a decrease of fluorescence efficiency. Thus a facile approach for tuning the color and intensity of fluorescent polymers has been developed by the control of polymer degree, which should be of particular interest for the design of fluorescent probe possessing color tunability.