School of Chemistry - Research Publications
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ItemHighly Efficient Luminescent Solar Concentrators by Selective Alignment of Donor-Emitter Fluorophores(AMER CHEMICAL SOC, 2019-04-23)Vertically aligning fluorophores to the surface of a waveguide is known to be an effective approach to improve the optical quantum efficiency (OQE) of luminescent solar concentrators (LSCs). While the chromophore alignment assists waveguiding of the emitted photons to the LSC edges, it also significantly reduces the light-harvesting properties of the LSC. We report here a fluorophore pair consisting of a sphere-shaped energy donor and a rod-shaped emitter that was incorporated in LSCs to provide selective fluorophore alignment to address the reduced incident-light absorption issue. A liquid-crystal polymer matrix was used to perpendicularly align the rod-shaped acceptors to a favorable orientation for light guiding, while the sphere-shaped donor was randomly oriented to maintain its light-absorbing properties. The OQE of LSC devices with this selectively aligned donor-acceptor fluorophore system is 78% without significant loss of light-harvesting capability.
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ItemFRET-enhanced photoluminescence of perylene diimides by combining molecular aggregation and insulation(Royal Society of Chemistry, 2020-07-14)The photoluminescence quantum yield (ϕPL) of perylene diimide derivatives (PDIs) is often limited by aggregation caused quenching (ACQ) at high concentration or in the neat solid-state. Energy transfer in high dye concentration systems is also a key factor in determining ϕPL as a result of energy funneling to trap sites in the sample. By tuning the substituents, we present two classes of PDIs with aggregation and insulation of the PDI core. By combining these fluorophores in a polymer film, we demonstrate highly emissive samples (85% ϕPL) at high concentration (140 mM or 20% w/w). Experimental and theoretical studies provide insight into why such a combination is necessary to achieve high ϕPL. While insulated fluorophores maintain respectable ϕPL at high concentration, an improved ϕPL can be achieved in the presence of appropriately oriented fluorophore aggregates as emissive traps. The theoretical calculations show that the relative orientation of aggregated monomers can result in energetic separation of localized states from the charge-transfer and bi-excitonic states thereby enabling high ϕPL.
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ItemTetraphenylethene 9,10-Diphenylanthracene Derivatives - Synthesis and Photophysical Properties(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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ItemSingle Isomer of Indene-C70 Bisadduct-Isolation and Performance in Bulk Heterojunction Solar Cells(AMER CHEMICAL SOC, 2014-02-25)
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ItemRegioselective synthesis of fullerene multiadducts via tether-directed 1,3-dipolar cycloaddition(ROYAL SOC CHEMISTRY, 2015)The regioselective synthesis of fullerene multiadducts was achieved from commercially available reagents in one pot over two steps. The configuration of the isolated regioisomers was determined using various NMR methods, UV-vis spectroscopy and electrochemical analysis with the structure of one isomer confirmed by single crystal X-ray analysis. Interesting variation in regioselectivity was observed when different amino acid reagents were used in the reactions. Theoretical calculations and additional experiments, such as deuterium exchange, led to a proposed mechanism for the regioselective product formation.
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ItemHighly Fluorescent Molecularly Insulated Perylene Diimides: Effect of Concentration on Photophysical Properties(AMER CHEMICAL SOC, 2017-10-10)
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ItemAmine-Substituted Diazocine Derivatives - Synthesis, Structure, and Photophysical Properties(WILEY-V C H VERLAG GMBH, 2018-11)Abstract A series of amine‐substituted diazocines were synthesized in three steps from methyl 2‐aminobenzoate or methyl 3‐aminonaphtholate. The saddle‐shaped diazocine compounds showed similar interplane angle of 75° despite the different steric bulk of the amine substituents. In electrochemical experiments, these diazocines showed irreversible reduction most likely producing indolo[3,2‐b]indoles rather than forming the 10‐electron planar aromatic species. The carbazole‐substituted naphthodiazocines showed the most interesting photophysical properties with evidence of transition from the saddle‐shaped ground state to a planar excited state geometry.
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ItemOne-pot selective synthesis of a fullerene bisadduct for organic solar cell applications(ROYAL SOC CHEMISTRY, 2015)A single isomer of fullerene bisadduct, PC61PF, was obtained from commercially available fullerene derivative, PC61BM, in one pot over two steps. The tether-directed remote functionalization approach provided a very simple and fast method to produce a single isomer of fullerene bisadduct with good yield and easy purification. Bulk heterojunction organic solar cells containing the bisadduct was fabricated and tested.