Study of Luminescent Cyclometalated Iridium(III) and Ruthenium(II) - Functionalized Polymeric Materials


Student thesis: Doctoral Thesis

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Award date9 Aug 2022


Functional polymeric materials having active sites on the polymer backbones have become an important cornerstone of the functional materials in modern industry because these materials have many applications, including photosensitization, catalysis, biomedical and pharmaceutical applications, selective separation technology, and energy conversion. Amongst, luminescent polymeric materials with high photostability and thermal stability are promising candidates for applications. Through immobilizing phosphorescent cyclometalated Ir(III) and bis(diimine) Ru(II) complexes onto the polymer support materials, the photophysical and excited state properties can be conveyed to the whole polymeric system, which have been rarely explored. It is anticipated that polymeric materials immobilized with the phosphorescent transition metal complexes could serve as recyclable heterogeneous photocatalysts and luminescent chemosensors. To develop luminescent chemosensors, the polymer support materials should contain receptor moieties for binding the targeted analytes. On the other hand, the specific binding properties of such polymers can be enforced as oral sequestrants for biomedical applications.

To develop recyclable heterogeneous photocatalysts, cyclometalated Ir(III) complexes have been anchored on different types of polymer support materials. These photocatalysts show dual emissive properties with a major MLCT phosphorescence and a minor polymer-based emission. The MLCT phosphorescence can be oxidatively quenched when suspended in the solution of perfluorohexyl iodide to generate perfluorohexyl radical that drives the photoredox addition and amidation reactions. The photocatalytic activity and performance of these photocatalysts have been studied. Some of these photocatalysts show excellent recyclability. Based on these results, the criteria for designing efficient and recyclable heterogeneous immobilized photoredox catalysts have been discussed.

With the immobilization method developed for the iridium-based polymer-supported photocatalysts, the design and synthesis of luminescent trimethylamine (TMA) sensor have been established by immobilizing cyclometalated iridium(III) complex onto a TMA-imprinted polymer. Detailed study shows that the emission properties of the TMA sensor can serve as a reporter for the binding of TMA on the imprinting sites, thus providing a sensitive, selective, and fast detection of TMA in both aqueous solutions and gaseous states. For the filter paper-loaded sensor, the phosphorescence is quenched within 5 s upon exposure to TMA vapor with the detection limits of 9 ppm under argon and 15 ppm in the air atmosphere. With this emission response toward TMA vapor, the application of the filter paper-loaded TMA sensor as a visual indicator for seafood spoilage is demonstrated.

Apart from the TMA target, the indole-imprinted polymer has also been fabricated as a selective indole adsorbent. By covalent attachment of tris(diimine) ruthenium(II) complex on the indole-imprinted polymer, the phosphorescent signal can serve as a luminescent sensor for the monitoring of the binding event between the indole-imprinted polymer and indole molecules. On the other hand, the biomedical application of indole capturing properties of the polymer has been evaluated. By selective removal of indole in the digestive tract, the toxic indoxyl sulfate level in plasma can be lowered. The feasibility of biomedical application has been evaluated by in vitro cytotoxicity study on human colon mucosal epithelial cell line NCM-460 and human epithelial colorectal adenocarcinoma cell line Caco-2, acute toxicity study in C57B/L6 mice as well as in vivo physiological study on db/db DN mice upon uptaking indole-imprinted MIP.