UBC Theses and Dissertations
Thermally activated delayed fluorescence materials as organic photosensitizers in small molecules and polymers Polgar, Alexander M.
Photosensitizer molecules play a crucial role in materials and life sciences. Efforts to improve their performance and reduce the associated costs are vital for advancing environmentally friendly light-driven technologies. This thesis examines photosensitizers that make use of thermally activated delayed fluorescence (TADF) and explores efforts to develop emitters with application-tailored properties. The key finding is the diversity of accessible excited state pathways in TADF sensitizers, which can be tuned by both molecular and supramolecular approaches to suit a problem. Organic light emitting diodes (OLEDs) are the future of solid-state lighting, but the full realization of this technology will require new materials that can be manufactured cost-effectively with high performance for the conversion of electricity to light. Polymeric TADF emitters are attractive in this respect because they can function as the emissive elements of OLEDs and be deposited by low-cost solution methods. This thesis makes use of 2,4,6-triphenylpyrimidine-based acrylic monomers which exhibit bright, colour-tunable TADF, potentially suitable for use in solution-processed OLEDs when copolymerized with a host monomer. These same monomers can also function as sensitizers of fluorescent emission in terpolymers containing a fluorescent monomer as an energy acceptor for bright and colour-pure TADF-sensitized fluorescence (TAF). The efficiency with which energy is transferred in TAF is found to depend on polymer architecture, with block copolymers limiting emission quenching interactions and rigid bottlebrush copolymers providing optimal control over the interface between energy donor and acceptor at the nanoscale. TADF sensitizers are also attractive in photocatalysis because of the diversity of their accessible excited states. A series of TADF donor-acceptor conjugates based on 2,4,6- triphenylpyrimidine acceptor and 9,10-dihydro-9,9-dimethylacridine (DMA) donors were prepared as photosensitizers for organocatalyzed organic atom transfer radical polymerization (OATRP). The donor is either unmodified DMA or functionalized with methylphenyl or methoxyphenyl groups. The donor-modification strategy is found to dramatically improve OATRP performance by imparting redox reversibility and high rates of dissociative electron transfer, as well as preventing unwanted side-reactivity in the excited state. With the methoxyphenyl derivative, methacrylic monomers could be polymerized with low dispersity (≤1.3), high initiator efficiency and chain-end fidelity, and molecular weights up to 40 kDa.
Item Citations and Data
Attribution-NonCommercial-NoDerivatives 4.0 International