School of Chemistry - Research Publications

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 591
  • Item
    Thumbnail Image
    John Atherton Young 1936–2004
    Rae, ID (CSIRO Publishing, 2024)
    John Atherton Young (1936–2004) graduated in medicine at the University of Queensland and undertook research in physiology at the Kanematsu Institute in Sydney for which he was awarded his PhD. After postdoctoral studies in Germany, he joined the department of physiology at the University of Sydney, rising to professor, then Dean of the Faculty of Medicine and finally Pro-Vice-Chancellor for Health Sciences. His research on the physiology of epithelial ducts, beginning with those of the kidney but later centring on salivary glands and the pancreas, brought him international recognition as a leader in the field. He made significant contributions to professional societies and was recognised with international and national awards including membership of the Order of Australia. A bronze portrait head of Young by sculptor Dan Lake is displayed in the foyer of the Edward Ford building at the University of Sydney. He was a man of great culture, a witty conversationalist and a great scientist.
  • Item
    No Preview Available
    Resolving conjugated polymer film morphology with polarised transmission and time-resolved emission microscopy
    Xu, Y ; Sun, L ; Ghiggino, KP ; Smith, TA (IOP Publishing, 2024-07-01)
    The alignment of chromophores plays a crucial role in determining the optoelectronic properties of materials. Such alignment can make interpretation of fluorescence anisotropy microscopy (FAM) images somewhat ambiguous. The time-resolved emission behaviour can also influence the fluorescence anisotropy. This is particularly the case when probing excitation energy migration between chromophores in a condensed phase. Ideally information concerning the chromophoric alignment, emission decay kinetics and fluorescence anisotropy can be recorded and correlated. We report on the use of polarised transmission imaging (PTI) coupled with both steady-state and time-resolved FAM to enable accurate identification of chromophoric alignment and morphology in thin films of a conjugated polydiarylfluorene. We show that the combination of these three imaging modes presents a comprehensive methodology for investigating the alignment and morphology of chromophores in thin films, particularly for accurately mapping the distribution of amorphous and crystalline phases within the thin films, offering valuable insights for the design and optimization of materials with enhanced optoelectronic performance.
  • Item
    Thumbnail Image
    Chemical vapor deposition growth of phase-selective inorganic lead halide perovskite films for sensitive photodetectors
    Xu, W ; Niu, M ; Yang, X ; Chen, H ; Cai, X ; Smith, TA ; Ghiggino, KP ; Hao, X (ELSEVIER SCIENCE INC, 2021-01)
    Inorganic lead halide perovskites are attractive optoelectronic materials owing to their relative stability compared to organic cation alternatives. The chemical vapor deposition (CVD) method offers potential for high quality perovskite film growth. The deposition temperature is a critical parameter determining the film quality owing to the melting difference between the precursors. Here, perovskite films were deposited by the CVD method at various temperatures between 500−800 °C. The perovskite phase converts from CsPb2Br5 to CsPbBr3 gradually as the deposition temperature is increased. The grain size of the perovskite films also increases with temperature. The phase transition mechanism was clarified. The photoexcited state dynamics were investigated by spatially and temporally resolved fluorescence measurements. The perovskite film deposited under 750 °C condition is of the CsPbBr3 phase, showing low trap-state density and large crystalline grain size. A photodetector based on perovskite films shows high photocurrent and an on/off ratio of ∼2.5 × 104.
  • Item
    Thumbnail Image
    Excitonic Processes in a Conjugated Polyelectrolyte Complex
    Nitneth, DT ; Hutchison, JA ; Ghiggino, KP (CSIRO Publishing, 2020)
    In aqueous solution, a di-sulfonated phenylenevinylene polymer (DPS-PPV) forms a complex with non-ionic poly(vinyl alcohol) (PVA) leading to absorption spectroscopic shifts and a dramatic (6-fold) increase in DPS-PPV fluorescence intensity. Spectroscopic investigations demonstrate that the complexation with PVA and other neutral polymers results in conformational changes in the DPS-PPV chains that lead to the removal of non-fluorescent energy traps and results in the observed increase in fluorescence in the bulk solution. Single molecule fluorescence measurements of DPS-PPV chains dispersed on glass and in PVA films confirm that efficient exciton energy transfer occurs within each photo-excited DPS-PPV chain and that the observed increase in fluorescence intensity in the PVA film environment is also associated with fewer quenching sites. The results highlight the importance of conjugated polyelectrolyte conformation on exciton relaxation pathways.
  • Item
    Thumbnail Image
    Revealing the Role of Methylammonium Chloride for Improving the Performance of 2D Perovskite Solar Cells
    Zheng, F ; Zuo, C ; Niu, M ; Zhou, C ; Bradley, SJ ; Hall, CR ; Xu, W ; Wen, X ; Hao, X ; Gao, M ; Smith, TA ; Ghiggino, KP (American Chemical Society, 2020-06-10)
    Layered perovskite films, composed of two-dimensional (2D) Ruddlesden–Popper perovskites (RPPs), show improved stability compared to their conventional three-dimensional (3D) counterparts in perovskite solar cells (PSCs). However, 2D PSCs exhibit a lower power conversion efficiency (PCE), which has been attributed to compositional inhomogeneity and nonuniform alignment of the 2D perovskite phases. Methylammonium chloride (MACl) has been adopted as an additive to improve the PCE and the operational stability of 2D PSCs, although the role of MACl in performance enhancement is unclear. In this work, time- and spatially resolved fluorescence and absorption techniques have been applied to study the composition and charge carrier dynamics in MACl-doped BA2MA4Pb5I16 (⟨n⟩ = 5) layered perovskite films. The inhomogeneous phase orientation distribution in the direction orthogonal to the substrate for undoped layered perovskite films undergoes reorganization upon MACl doping. Based on structural and crystallographic analyses, it is revealed that MACl can facilitate the crystallization of small-n 2D perovskite phases at the cost of consuming an increased amount of BA cations. Consequently, an increase in the thickness of large-n 2D perovskite phases accompanies their enhanced perpendicular alignment ([101] crystalline orientation) to the substrate, which facilitates charge carrier transport and collection by electrodes. The defect passivation of the MACl-doped layered perovskite film provided by the small-n phase is also beneficial to the photovoltaic performance of the PSC device. A maximum PCE (∼14.3%) was achieved at 6 mol % MACl doping, with this optimum level influenced by the increased interfacial roughness of the layered perovskite film caused by the edges of small-n perovskite flakes emerging on the front surface.
  • Item
    Thumbnail Image
    Morphological Requirements for Nanoscale Electric Field Buildup in a Bulk Heterojunction Solar Cell
    Schwarz, KN ; Mitchell, VD ; Khan, S-U-Z ; Lee, C ; Reinhold, A ; Smith, TA ; Ghiggino, KP ; Jones, DJ ; Rand, BP ; Scholes, GD (AMER CHEMICAL SOC, 2021-01-14)
    The morphology of organic semiconductors is critical to their function in optoelectronic devices and is particularly crucial in the donor-acceptor mixture that comprises the bulk heterojunction of organic solar cells. Here, energy landscapes can play integral roles in charge photogeneration, and recently have been shown to drive the accumulation of charge carriers away from the interface, resulting in the buildup of large nanoscale electric fields, much like a capacitor. In this work we combine morphological and spectroscopic data to outline the requirements for this interdomain charge accumulation, finding that this effect is driven by a three-phase morphology that creates an energetic cascade for charge carriers. By adjusting annealing conditions, we show that domain purity, but not size, is critical for an electro-absorption feature to grow-in. This demonstrates that the energy landscape around the interface shapes the movement of charges and that pure domains are required for charge carrier buildup that results in reduced recombination and large interdomain nanoscale electric fields.
  • Item
    Thumbnail Image
    Spectroscopic and Dynamic Properties of Electronically Excited Pendant Porphyrin Polymers with Backbones of Differing Flexibility
    Stevens, AL ; Awuku, S ; Ghiggino, KP ; Hao, Y ; Novakovic, S ; Steer, RP ; White, JM (American Chemical Society, 2020-12-24)
    A zinc porphyrin-pendant norbornene polymer with a rigid backbone characterized by a 2:1 E/Z isomeric structure ratio has been synthesized, and its spectroscopic and photophysical properties are examined. Zinc tetraphenylporphyrin, the porphyrin-substituted norbornene monomer, and a previously reported zinc porphyrin-pendant polymer with a flexible polymethylene backbone have been used as comparators. Unlike its flexible counterpart, the rigid norbornene polymer exhibits clear exciton splitting of its Soret band, much more rapid relaxation rates of its excited singlet states, and a very small yield of an unusually short-lived triplet state. Unlike the flexible pendant polymer, which exhibits excimeric S2 fluorescence as a result of chromophore rotation, anti-Kasha emission from the norbornene polymer originates primarily from the unperturbed porphyrin E region. The low triplet yield in the polymer is attributed to greatly increased rates of competing internal conversion within the singlet manifold. Nevertheless, upconverted delayed fluorescence that is quenched by oxygen is observed upon intense steady-state Q-band excitation of degassed polymer solutions, signaling direct triplet involvement. Consistent with the polymer’s rigid structure, this biexcitonic process is assigned to ultrafast singlet exciton migration and triplet–triplet annihilation following absorption of a second photon by the small steady-state concentration of polymer triplets.
  • Item
    Thumbnail Image
    Electronic spectroscopy and photophysics of calix[4]azulene
    Stevens, AL ; Yeow, C ; White, JM ; Bradley, SJ ; Ghiggino, KP ; Steer, RP (ELSEVIER SCIENCE SA, 2021-01-15)
    Calix[4]azulene is a non-alternant aromatic calixarene composed of four azulene chromophores linked by methylene groups. Its photochemical stability, photophysical properties and an analysis of its electronic spectra are reported using monomeric azulene as a known reference standard. The molecule is stable when excited in its visible and near uv absorptions and, unlike azulene, produces no measurable “anti-Kasha” fluorescence when excited to its second excited singlet state, S2. This lack of fluorescence places the lifetime of the initially excited, photochemically stable S2 species at less than 1 picosecond. A significant, bathochromic shift of the S2 absorption band system in the calixarene, and the appearance of an additional weak, broad absorption immediately to the red signals significant intramolecular chromophore interaction. Femtosecond transient absorption spectroscopy using excitation in this red-shifted tail of the S2 band system reveals a very weak transient signal most of which decays within one ps, but with suggestions of a slightly longer-lived underlying component. No longer-lived T1 triplet transient is observed. A complete analysis of the data using monomeric azulene as a reference suggests, following elimination of several alternate mechanisms, that the initially excited S2 species may be relaxing via a novel singlet-singlet fission process.
  • Item
    Thumbnail Image
    Ultrafast Nanodrum-on-Chip Pixels
    Li, J ; Hutchison, JA ; Smith, D ; Wu, H ; Mulvaney, P (AMER CHEMICAL SOC, 2024-03-15)
    Environmentally friendly, ultrafast display pixels of micrometer sizes are fabricated with nanometer-thick gold films and Si/SiO2 wafers. The color displayed is due to both the plasmon response of the gold film and the optical interference from the Fabry-Peerot cavity formed by the underlying silicon substrate, the semitransparent gold film and the air gap between them. When an electric potential is applied to the gold film, the electrostatic force induces an attraction between the gold film and the silicon wafer. Due to the flexibility of the film, the size of the air gap changes, resulting in a changing color. By applying different driving signals, we have achieved cyan, magenta, and yellow reflected colors. The maximum switching rate of the pixel is primarily determined by the thickness dependence of the metal drum and its Young's modulus and is typically in the MHz regime.
  • Item
    No Preview Available
    Fingerprints of Chalcogen Bonding Revealed Through 77Se-NMR.
    Fellowes, T ; Sani, MA ; White, JM (Wiley, 2024-03-20)
    77Se-NMR is used to characterise several chalcogen bonded complexes of derivatives of the organoselenium drug ebselen, exploring a range of electron demand. NMR titration experiments support the intuitive understanding that chalcogen bond donors bearing more electron withdrawing substituents give rise stronger chalcogen bonds. The chemical shift of the selenium nucleus is also shown to move upfield as it participates in a chalcogen bond. Solid-state NMR is used to explore chalcogen bonding in co-crystals. Due to the lack of molecular reorientation on the NMR timescale in the solid state, the shape of the chemical shift tensor can be determined using this technique. A range of co-crystals are shown to have extremely large chemical shift anisotropy, which suggests a strongly anisotropic electron density distribution around the selenium atom. A single crystal NMR experiment was conducted using one of the co-crystals, affording the absolute orientation of the chemical shift tensor within the crystal. This showed that the selenium nucleus is strongly shielded in the direction of the chalcogen bond (due to the approach of the lone pair of the Lewis base), and strongly deshielded in the perpendicular direction. The orientation of the deshielded axis is consistent with the presence of a second σ-hole which is not participating in a chalcogen bond, showing the profound effect of electron density anisotropy on the chemical shift.