UBC Theses and Dissertations

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UBC Theses and Dissertations

Red and near-infrared luminescent materials for biological imaging Paisley, Nathan R.


Fluorescence imaging is a critical tool for visualizing cellular structures and complex biological processes; however, background autofluorescence from molecules and structures within the cell can severely reduce the signal-to-noise ratio (SNR) and imaging quality. Time-resolved imaging (TRI) and two-photon excited fluorescence (2PEF) microscopy are two techniques that can be used to remove background autofluorescence and improve SNR. Imaging probes with long lifetime emission are required to utilize TRI techniques. Purely organic materials with properties such as thermally activated delayed fluorescence (TADF) exhibit long lifetime photoluminescence. Additionally, to image living samples, luminescent imaging probes should ideally absorb and emit within the biological transparency window (650–1350 nm), but efficient TADF emission within this range is rare. Work described in this thesis uses materials exhibiting TADF or 2PEF to develop biological imaging probes with emission within the biological transparency window. These materials were synthesized as small molecules or polymerized with a semiconductor host and formed into polymer nanoparticles called polymer dots (Pdots) that retain the photophysical properties required for TRI or 2PEF microscopy. New deep-red/near-infrared (NIR) emissive TADF monomers were synthesized and the mechanism behind TADF was explored using density functional theory (DFT). Pdots with a cell-penetrating peptide mimic shell were demonstrated to efficiently enter multiple cell lines in under 30 minutes while retaining high cell viability. Proof-of-concept experiments for the use of these Pdots in TRI demonstrated that the TADF emission can be separated from background fluorescence. This work represents some of the first demonstrations of Pdots containing red to NIR emissive TADF polymers for cellular imaging. For materials exhibiting 2PEF, it was shown that the electron donor moieties effect on planarity directly correlates to the relative strength of 2PEF within a series. Additionally, in the closely related field of semiconductor polymers, reactive semifluorinated polymers were investigated for the efficient synthesis of a series of polymers based on p-type and n-type semiconductor motifs commonly found in organic light-emitting diodes (OLEDs), organic thin-film transistors (OTFTs), and organic photovoltaics (OPVs). Experiments demonstrating that semifluorinated polymers can provide a useful building block in the synthesis of organic electronic materials were conducted.

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