School of Chemistry - Research Publications

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    Amplifying the Negative Solvatochromism of Pyridinium Phenolates via Fluorene Conjugation
    Zharinova, I ; Saker Neto, N ; Wong, WWH (AMER CHEMICAL SOC, 2023-12-19)
    New chromophores carrying a donor phenolate group and an acceptor pyridyl moiety separated by a fluorene spacer are reported. A progressive elongation of the systems was achieved by the introduction of an additional phenyl ring and one or two vinyl linkers using Suzuki-Miyaura or Horner-Wadsworth-Emmons couplings. Zwitterionic forms FL1-FL5 of these donor-bridge-acceptor molecules were generated through consequent N-methylation and deprotonation reactions leading to large redshifts in absorbance maxima. UV-vis absorbance studies also revealed a negative solvatochromic behavior, with a smooth bathochromic shift observed upon decreasing the solvent polarity. Notably, examples FL1a and FL3 exhibited wide solvatochromic shifts of 235 and 297 nm, respectively, as the solvent polarity gradually lowered from polar water to less polar pyridine. Remarkably, the magnitude of the shift for FL3 was even greater than that of Reichardt’s dye (253 nm) in the same solvent range, which is known to be one of the best performing solvatochromic dyes reported. Apart from extending the conjugation, the fluorene moiety also allows facile side chain engineering, making these solvatochromic dyes attractive candidates for medium-polarity indicators and sensors.
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    Challenges and opportunities for innovation in bioinformed sustainable materials
    Stuart-Fox, D ; Ng, L ; Barner, L ; Bennett, ATD ; Blamires, SJ ; Elgar, MA ; Evans, AR ; Franklin, AM ; Holtta-Otto, K ; Hutchison, JA ; Jativa, F ; Jessop, A-L ; Kelley, J ; McGaw, J ; Mei, J ; Mirkhalaf, M ; Musameh, M ; Neto, C ; O'Connor, AJ ; Schork, T ; Schroder-Turk, GE ; Voelcker, NH ; Wang, A ; Watson, GS ; Watson, JA ; Wesemann, L ; Wong, WWH (SPRINGERNATURE, 2023-10-04)
    Abstract Nature provides a rich source of information for the design of novel materials; yet there remain significant challenges in the design and manufacture of materials that replicate the form, function, and sustainability of biological solutions. Here, we identify key challenges and promising approaches to the development of materials informed by biology. These challenges fall into two main areas; the first relates to harnessing biological information for materials innovation, including key differences between biological and synthetic materials, and the relationship between structure and function. We propose an approach to materials innovation that capitalizes on biodiversity, together with high-throughput characterization of biological material architectures and properties, linked to environmental and ecological context. The second area relates to the design and manufacture of bioinformed materials, including the physical scale of material architectures and manufacturing scale up. We suggest ways to address these challenges and promising prospects for a bioinformed approach to materials innovation.
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    Multi-resonance TADF in optical cavities: suppressing excimer emission through efficient energy transfer to the lower polariton states
    Cho, I ; Kendrick, WJ ; Stuart, AN ; Ramkissoon, P ; Ghiggino, KP ; Wong, WWH ; Lakhwani, G (Royal Society of Chemistry, 2023-11-07)
    Thermally activated delayed fluorescence (TADF) emitters suffer from molecular aggregation that limits their applicability in light emitting devices. Aggregation-induced excimer formation often leads to a larger Stokes shift, broader emission spectrum, and reduced emission quantum yields, limiting emitter dye loading to a few weight percent in organic light emitting devices. Here, we demonstrate suppression of excimer emission by dispersing a synthesised multi-resonance TADF emitter dye (OQAO(mes)2) in a PMMA host matrix and embedding the host–guest photoactive layer into an optical cavity. Rabi splitting up to 0.24 eV is obtained at 35 wt% dye loading. Under the strong coupling regime, prompt and delayed emission through excimer states is suppressed due to efficient energy transfer to the lower polariton (LP) states, demonstrated by the blue shift of the emission spectrum and narrowing of the emission linewidth. We also observe an increase in reverse intersystem crossing (RISC) rate constants up to 33% that we attribute to a decrease in activation energy by ≈2kT. This work highlights that strong light-matter interactions can be exploited to overcome aggregation-induced excimer losses providing a pathway towards efficient organic light-emitting diodes with high colour purity and organic semiconductor polariton lasing.
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    A luminescent solar concentrator ray tracing simulator with a graphical user interface: features and applications
    Zhang, B ; Yang, H ; Warner, T ; Mulvaney, P ; Rosengarten, G ; Wong, WWH ; Ghiggino, KP (IOP PUBLISHING LTD, 2020-07)
    A Monte-Carlo ray tracing simulator with a graphical user interface (MCRTS-GUI) has been developed to provide a quantitative description, performance evaluation and photon loss analysis of luminescent solar concentrators (LSCs). The algorithm is applied to several practical LSC device structures including multiple dyes in the same waveguiding layer, and structures where a dye layer is sandwiched between clear substrates. The effect of the host matrix absorption and the influence of the neighboring layers are investigated. Validations demonstrate that the MCRTS-GUI developed provides a reliable and accurate description of LSC performance. Code for the mixed-dye single layer configuration is converted into a ray-tracing package with a user-friendly interface and is made available as open source software.
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    Consensus statement: Standardized reporting of power-producing luminescent solar concentrator performance
    Yang, C ; Atwater, HA ; Baldo, MA ; Baran, D ; Barile, CJ ; Barr, MC ; Bates, M ; Bawendi, MG ; Bergren, MR ; Borhan, B ; Brabec, CJ ; Brovelli, S ; Bulovic, V ; Ceroni, P ; Debije, MG ; Delgado-Sanchez, J-M ; Dong, W-J ; Duxbury, PM ; Evans, RC ; Forrest, SR ; Gamelin, DR ; Giebink, NC ; Gong, X ; Griffini, G ; Guo, F ; Herrera, CK ; Ho-Baillie, AWY ; Holmes, RJ ; Hong, S-K ; Kirchartz, T ; Levine, BG ; Li, H ; Li, Y ; Liu, D ; Loi, MA ; Luscombe, CK ; Makarov, NS ; Mateen, F ; Mazzaro, R ; McDaniel, H ; McGehee, MD ; Meinardi, F ; Menendez-Velazquez, A ; Min, J ; Mitzi, DB ; Moemeni, M ; Moon, JH ; Nattestad, A ; Nazeeruddin, MK ; Nogueira, AF ; Paetzold, UW ; Patrick, DL ; Pucci, A ; Rand, BP ; Reichmanis, E ; Richards, BS ; Roncali, J ; Rosei, F ; Schmidt, TW ; So, F ; Tu, C-C ; Vahdani, A ; van Sark, WGJHM ; Verduzco, R ; Vomiero, A ; Wong, WWH ; Wu, K ; Yip, H-L ; Zhang, X ; Zhao, H ; Lunt, RR (CELL PRESS, 2022-01-19)
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    Energy Transfer between CdZnS Quantum Dots and Perylene Diimide Dyes
    Wu, N ; Kirkwood, N ; Neto, NS ; Pervin, R ; Mulvaney, P ; Wong, WWH (American Chemical Society, 2023-01-25)
    QD-dye systems are promising models for artificial photosynthesis and down converter systems for LEDs and displays. To better understand the factors controlling energy transfer from the QDs to the dyes, we fabricated a series of CdxZn1-xS/ZnS quantum dot (QD)-perylene diimide (PDI) composite nanocrystals. The core-shell CdxZn1-xS/ZnS QDs were chosen for better control of surface chemistry and for control of photophysical properties through core composition. The PDIs were designed with bulky substituents to reduce dye-dye aggregation effects. Energy transfer efficiency was found to depend upon both the length of the anchoring alkyl chain and the type of terminal anchoring group. The maximum energy transfer efficiency of 91% from QDs to PDIs was achieved with composites containing PDIs with carboxylic acid anchoring groups and longer alkyl chains. It was found that composites with carboxylic acid anchors exhibited greater photostability than composites with amine anchors. Longer alkyl chains also led to greater photostability. Conversely, shorter chain alkanes promoted faster aggregation of the nanocrystal composites.
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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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    Harvesting Triplet Excitons in High Mobility Emissive Organic Semiconductor for Efficiency Enhancement of Light-Emitting Transistors
    Gao, C ; Shukla, A ; Gao, H ; Miao, Z ; Zhang, Y ; Wang, P ; Luo, G ; Zeng, Y ; Wong, WWH ; Smith, TA ; Lo, S-C ; Hu, W ; Namdas, EB ; Dong, H (Wiley, 2023-03-29)
    Organic light-emitting transistors (OLETs), a kind of highly integrated and minimized optoelectronic device, demonstrate great potential applications in various fields. The construction of high-performance OLETs requires the integration of high charge carrier mobility, strong emission, and high triplet exciton utilization efficiency in the active layer. However, it remains a significant long-term challenge, especially for single component active layer OLETs. Herein, the successful harvesting of triplet excitons in a high mobility emissive molecule, 2,6-diphenylanthracene (DPA), through the triplet-triplet annihilation process is demonstrated. By incorporating a highly emissive guest into the DPA host system, an obvious increase in photoluminescence efficiency along with exciton utilization efficiency results in an obvious enhancement of external quantum efficiency of 7.2 times for OLETs compared to the non-doped devices. Moreover, well-tunable multi-color electroluminescence, especially white emission with Commission Internationale del'Eclairage of (0.31, 0.35), from OLETs is also achieved by modulating the doping concentration with a controlled energy transfer process. This work opens a new avenue for integrating strong emission and efficient exciton utilization in high-mobility organic semiconductors for high-performance OLETs and advancing their related functional device applications.
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    Measured power conversion efficiencies of bifacial luminescent solar concentrator photovoltaic devices of the mosaic series
    Aghaei, M ; Pelosi, R ; Wong, WWH ; Schmidt, T ; Debije, MG ; Reinders, AHME (WILEY, 2022-07)
    Abstract The optical and electrical performances of varied configurations of visually attractive mosaic cubical luminescent solar concentrator photovoltaic (LSC PV) devices have been measured. These new designs of LSC PV devices consist of four cubical lightguides containing commercially available fluorophores with edge‐ and bottom‐mounted silicon solar cells. The 1 cm3 cubical component LSC PVs are made of poly (methyl methacrylate) (PMMA) doped by dyes from 10 to 150 ppm. The lightguides are covered with bifacial silicon solar cells at their edges and/or bottom and connected in series or parallel, depending on the device configuration. In total, 19 different configurations of mosaic LSC PV devices have been experimentally evaluated in this study.