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Ensuring long-term photostability in the design of luminescent materials remains a challenge that is often addressed at the molecular level. This consideration must be balanced with other optical properties such as emission wavelength, photoluminescence quantum yield (ΦF or PLQY), and colour purity, as well as physical properties such as solubility and thermal stability. Molecular rigidification is a promising means to improve photostability, ensuring suppression of molecular vibrations and photodegradation pathways. This strategy often enhances PLQY and colour purity as well, while requiring demanding synthetic procedures to prepare rigid and robust molecular motifs. By leveraging these advanced optical properties in conjunction with the design of purely organic materials exhibiting thermally activated delayed fluorescence (TADF), these materials can find use in a wide range of applications such as emitters in organic light emitting diodes (OLEDs), and as dyes for time-resolved imaging (TRI) in biology. Work described in this thesis involves the preparation of a range of luminophores exhibiting prompt nanosecond fluorescence, phosphorescence, and thermally activated delayed fluorescence, with tailored design features to render them useful for optoelectronic and biological applications. Deep-blue to deep-red emissive fluorophores were prepared using 1,3,4-oxadizole (ODA), s-heptazine (HAP), s-triazine (TRZ), and dibenzodipyridophenazine (BPPZ) motifs, with molecular rigidification explored using hexamethylazatriangulene (HMAT) as a planarized triarylamine electron-donating substituent. As some of these materials exhibited long-lived emission lifetimes and non-linear optical properties such as two-photon excited fluorescence (2PEF), efforts were made to render them water-dispersible in nanoparticle formulations for in vitro biological imaging applications. A range of strategies was examined to improve the versatility of luminophores using synthetic polymeric systems. In particular, living and controlled polymerization methods were used for incorporation of luminophores into polymers, resulting in solution-processable phosphorescent platinum (II) metallopolymers for OLED applications, and fluorescent polymers suitable for the preparation of polymer dot (Pdot) nanoparticles as bioimaging probes. Additionally, the challenge of rendering oxygen-sensitive TADF molecules water-dispersible was addressed using commercial surfactants for glassy organic dot (g-Odot) nanoparticles, in an effort to further explore a universal approach toward using any high-performance TADF material as a bioimaging probe. |
