School of Chemistry - Research Publications

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    Protection of Boronic Acids Using a Tridentate Aminophenol ONO Ligand for Selective Suzuki-Miyaura Coupling
    Simon, PM ; Castillo, JO ; Owyong, TC ; White, JM ; Neto, NS ; Wong, WWH (AMER CHEMICAL SOC, 2023-02-03)
    Boronic acid protecting group chemistry powerfully enhances the versatility of Suzuki-Miyaura cross-coupling. Prominent examples include trifluoroborate salts, N-methyliminodiacetic acid (MIDA) boronates, and 1,8-diaminonaphthalene boronamides. In this work, we present a bis(2-hydroxybenzyl)methylamine (BOMA) ligand that forms tridentate complexes with boronic acids much like the MIDA ligand but the deprotection is facilitated by organic acids. The BOMA boronates showed considerable stability in both aqueous base and acid, and a variety of chemoselective reactions were performed on these boronates, including selective Suzuki-Miyaura coupling, palladium-catalyzed borylation, ester hydrolysis, alkylation, lithiation-borylation, and oxidative hydroxydeboronation.
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    Medium effects on the fluorescence of Imide-substituted naphthalene diimides
    Pervin, R ; Manian, A ; Chen, Z ; Christofferson, AJ ; Owyong, TC ; Bradley, SJ ; White, JM ; Ghiggino, KP ; Russo, SP ; Wong, WWH (Elsevier, 2023-03-01)
    Naphthalene diimides (NDIs) are a common class of chromophores used in photon harvesting applications due to their functional malleability through substitution of the NDI core. However, some derivatives with substitution at the imide position of the NDI core only become emissive in electron-rich aromatic solvents. This study examines this phenomenon from both an experimental and theoretical perspective, in order to understand how NDIs interact with each other and the surrounding medium upon photoexcitation. We report the photophysical properties of cyclohexyl and several aromatic imide-substituted NDI derivatives, and show that fluorescence properties are strongly influenced by solvation in more electron-rich aromatic solvents (e.g. toluene, xylene, mesitylene). Theoretical modeling supports strong interactions, including ground state charge-transfer complexation, with aromatic solvents. In solid poly(methyl methacrylate) (PMMA) and poly(styrene) (PS) film media, both aggregation and complexation are shown to contribute to absorption and emission properties. The results also demonstrate that aromatic imide substituents not only act to provide steric bulk to the NDI chromophore but participate in interactions with the surrounding medium that affect the overall photophysical properties.
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    Limitations of conjugated polymers as emitters in triplet-triplet annihilation upconversion
    O'shea, R ; Gao, C ; Bradley, S ; Owyong, TC ; Wu, N ; White, JM ; Ghiggino, KP ; Wong, WWH (ROYAL SOC CHEMISTRY, 2021-11-29)
    Triplet–triplet annihilation upconversion performances for poly(phenylene-vinylene) emitters were investigated through a series of copolymers with bulky sidechains.
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    Tetraphenylethene 9,10-Diphenylanthracene Derivatives - Synthesis and Photophysical Properties
    Gao, C ; Seow, JY ; Zhang, B ; Hall, CR ; Tilley, AJ ; White, JM ; Smith, TA ; Wong, WWH (WILEY-V C H VERLAG GMBH, 2019-06)
    A series of tetraphenylethene 9,10-diphenylanthracene (TPE-DPA) derivatives have been synthesized, and their photophysical properties studied. Photoluminescence measurements in PMMA, neat films and nanoparticle dispersions reveal that different aggregation states are formed, which leads to different photophysical behavior. The triplet excited state properties were studied using Pt(II) octaethylporphyrin (PtOEP) as triplet sensitizer. Upconverted emission from the DPA moiety is observed in nanoparticle dispersions of each derivative. A higher upconverted emission intensity is observed in aerated (compared to deaerated) solutions of the derivatives following irradiation, which is attributed to oxidation of the TPE moiety. These results provide valuable insight for the design of AIE luminogens for triplet-triplet annihilation upconversion (TTA-UC).
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    Revealing the influence of steric bulk on the triplet-triplet annihilation upconversion performance of conjugated polymers
    O'shea, R ; Kendrick, WJ ; Gao, C ; Owyong, TC ; White, JM ; Ghiggino, KP ; Wong, WWH (NATURE PORTFOLIO, 2021-10-01)
    A series of poly(phenylene-vinylene)-based copolymers are synthesized using the Gilch method incorporating monomers with sterically bulky sidechains. The photochemical upconversion performance of these polymers as emitters are investigated using a palladium tetraphenyltetrabenzoporphyrin triplet sensitizer and MEH-PPV as reference. Increased incorporation of sterically bulky monomers leads to a reduction in the upconversion efficiency despite improved photoluminescence quantum yield. A phosphorescence quenching study indicates issues with the energy transfer process between the triplet sensitizer and the copolymers. The best performance with 0.18% upconversion quantum yield is obtained for the copolymer containing 10% monomer with bulky sidechains.
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    Optimising molecular rotors to AIE fluorophores for mitochondria uptake and retention
    OwYong, TC ; Ding, S ; Wu, N ; Fellowes, T ; Chen, S ; White, JM ; Wong, WWH ; Hong, Y (ROYAL SOC CHEMISTRY, 2020-12-07)
    Molecular rotors exhibit fluorescence enhancement in a confined environment and thus have been used extensively in biological imaging. However, many molecular rotors suffer from small Stokes shift and self-aggregation caused quenching. In this work, we have synthesised a series of red emissive molecular rotors based on cationic α-cyanostilbene. Profoundly enhanced aggregation-induced emission (AIE) properties and greatly widened Stokes shifts can be achieved by molecular engineering. With specificity to stain mitochondria, we demonstrate a simple approach to achieve cell uptake and retention upon tuning the pyridinium substituent of the dyes.
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    Synthesis and Solvatochromic Behavior of Zwitterionic Donor-Bridge-Acceptor Systems with Oligo(p -phenylene) Spacers
    Zharinova, I ; Saker Neto, N ; Owyong, TC ; White, JM ; Wong, WWH (Georg Thieme Verlag KG, 2021-01-15)
    Oligo(p-phenylene)s with a donor phenol group and an acceptor pyridinium moiety separated by one and two p-phenylene units were synthesized by the linear iterative Suzuki–Miyaura coupling method using aryl nonaflates as effective coupling reagents. Zwitterionic forms of these push–pull molecules were generated upon deprotonation of the phenol leading to large redshifts in absorbance maxima. UV-vis absorbance studies also revealed strong dependence of the band position on solvent polarity: a smooth bathochromic shift can be observed with the decrease of the solvent polarity. The molecule with one p-phenylene bridging unit showed the strongest solvatochromic characteristics in the series, spanning the range of 167 nm while moving from polar water to less polar N,N-dimethylformamide. The magnitude of this shift was close to Reichardt's dye — one of the most solvatochromic organic dyes known.
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    The performance of conjugated polymers as emitters for triplet-triplet annihilation upconversion
    O'Shea, R ; Gao, C ; Owyong, TC ; White, JM ; Wong, WWH (ROYAL SOC CHEMISTRY, 2021-03-21)

    Phenylene–ethynylene–anthracene copolymer was used as the emitter in triplet–triplet annihilation upconversion outperforming well-known poly(phenylene–vinylene)s.

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    A Molecular Chameleon for Mapping Subcellular Polarity in an Unfolded Proteome Environment
    Owyong, TC ; Subedi, P ; Deng, J ; Hinde, E ; Paxman, JJ ; White, JM ; Chen, W ; Heras, B ; Wong, WWH ; Hong, Y (WILEY-V C H VERLAG GMBH, 2020-06-15)
    Environmental polarity is an important factor that drives biomolecular interactions to regulate cell function. Herein, a general method of using the fluorogenic probe NTPAN-MI is reported to quantify the subcellular polarity change in response to protein unfolding. NTPAN-MI fluorescence is selectively activated upon labeling unfolded proteins with exposed thiols, thereby reporting on the extent of proteostasis. NTPAN-MI also reveals the collapse of the host proteome caused by influenza A virus infection. The emission profile of NTPAN-MI contains information of the local polarity of the unfolded proteome, which can be resolved through spectral phasor analysis. Under stress conditions that disrupt different checkpoints of protein quality control, distinct patterns of dielectric constant distribution in the cytoplasm can be observed. However, in the nucleus, the unfolded proteome was found to experience a more hydrophilic environment across all the stress conditions, indicating the central role of nucleus in the stress response process.
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    A Molecular Chameleon for Mapping Subcellular Polarity in an Unfolded Proteome Environment
    Owyong, TC ; Subedi, P ; Deng, J ; Hinde, E ; Paxman, JJ ; White, JM ; Chen, W ; Heras, B ; Wong, WWH ; Hong, Y (Wiley, 2020-06-15)
    Abstract Environmental polarity is an important factor that drives biomolecular interactions to regulate cell function. Herein, a general method of using the fluorogenic probe NTPAN‐MI is reported to quantify the subcellular polarity change in response to protein unfolding. NTPAN‐MI fluorescence is selectively activated upon labeling unfolded proteins with exposed thiols, thereby reporting on the extent of proteostasis. NTPAN‐MI also reveals the collapse of the host proteome caused by influenza A virus infection. The emission profile of NTPAN‐MI contains information of the local polarity of the unfolded proteome, which can be resolved through spectral phasor analysis. Under stress conditions that disrupt different checkpoints of protein quality control, distinct patterns of dielectric constant distribution in the cytoplasm can be observed. However, in the nucleus, the unfolded proteome was found to experience a more hydrophilic environment across all the stress conditions, indicating the central role of nucleus in the stress response process.