Browsing by Author "Hogan, Conor F."
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Item Access to the Parent Tetrakis(pyridine)gold(III) Trication, Facile Formation of Rare Au(III) Terminal Hydroxides, and Preliminary Studies of Biological Properties(2016-03-21) Dutton, Jason L.; Barnard, Peter J.; Hulett, Mark D.; Wilson, David J.; Hogan, Conor F.; Haghighatbin, Mohammad A.; Ryan, Gemma F.; Corbo, RobertIn this paper we report on the use of [NO][BF4] to access tricationic tetrakis(pyridine)gold(III) from Au powder, a species inaccessible using the more traditional (tetrahydrothiophene)AuCl route. It is then demonstrated that this family of compounds can be used to access new terminal Au(III) hydroxides, a challenging class of compounds, and the first crystallographically characterized examples employing bidentate ligands. Finally, preliminary biological studies indicate good activity for derivatives featuring polydentate ligands against the HeLa and PC3 cell lines but also strong inhibition of primary HUVEC cells.
Item Considering the Chemical Energy Requirements of the Tri-n-propylamine Co-Reactant Pathways for the Judicious Design of New Electrogenerated Chemiluminescence Detection Systems(2016-01-07) Francis, Paul S.; Hogan, Conor F.; Wilson, David J.; Doeven, Egan H.; Kerr, EmilyThe introduction of a ‘co-reactant’ was a critical step in the evolution of electrogenerated chemiluminescence (ECL) from a laboratory curiosity to a widely utilised detection system. In conjunction with a suitable electrochemiluminophore, the co-reactant enables generation of both the oxidised and reduced precursors to the emitting species at a single electrode potential, under the aqueous conditions required for most analytical applications. The most commonly used co-reactant is tri-n-propylamine (TPrA), which was developed for the classic tris(2,2’-bipyridine)ruthenium(II) ECL reagent. New electrochemiluminophores such as cyclometalated iridium(III) complexes are also evaluated with this co-reactant. However, attaining the excited states in these systems can require much greater energy than that of tris(2,2’-bipyridine)ruthenium(II), which has implications for the co-reactant reaction pathways. In this tutorial review, we describe a simple graphical approach to characterise the energetically feasible ECL pathways with TPrA, as a useful tool for the development of new ECL detection systems.
Item Facile Formation of Homoleptic Au(III) Trications via Simultaneous Oxidation and Ligand Delivery from [PhI(pyridine)2]2+(2014-09-03) Dutton, Jason L.; Barnard, Peter J.; Wilson, David J.; Hogan, Conor F.; Stringer, Bradley D.; Pell, Thomas P.; Corbo, RobertWe report the first examples of Au(III) tricationic complexes bound only by neutral monodentate ligands, which are a new class of gold reagents. Oxidative addition to the bis-pyridine Au(I) cation, [Au(4-DMAP)2]+, using a series of dicationic I(III) oxidants of the general form [PhI(L)2]2+ (L = pyridine, 4-DMAP, 4-cyanopyridine) allows ready access to homoleptic and pseudo-homoleptic Au(III) complexes [Au(4-DMAP)2(L)2]3+. The facile oxidative addition of Au(I) species additionally demonstrates the efficacy of PhI(L)2]2+ reagents as halide-free oxidants for Au(I). Comparisons are made via attempts to oxidize NHC-Au(I)Cl, where introduction of the chloride anion results in complex mixtures via ligand and chloride exchange, demonstrating the advantage of using the pyridine-based homoleptic compounds. The new Au(III) trications show intriguing reactivity with water, yielding dinuclear oxo-bridged and rare terminal Au(III)−OH complexes.
Item Iridium Complexes of N-Heterocyclic Carbene Ligands: Investigation into the Energetic Requirements for Efficient Electrogenerated Chemiluminescence(2014-09-22) Hogan, Conor F.; Wilson, David J.; Barnard, Peter J.; Quan, Linh M.; Stringer, Bradley D.A series of five heteroleptic Ir(III) complexes of the general form Ir(ppy)2(C∧C:) have been prepared (C∧C represents a bidentate cyclometalated phenyl-substituted imidazolylidene ligand). The five complexes arise from the cyclometalated phenyl ring of the NHC ligand being unsubstituted or having electron-donating (OMe and Me) or electron-withdrawing (Cl and F) groups at the 2- and 4- positions of the ring. The synthesized phenyl-substituted imidazole precursors, imidazolium salts, and Ir(III) complexes have been characterized by elemental analysis, NMR spectroscopy, cyclic voltammetry, and electronic absorption and emission spectroscopy. The molecular structures for two imidazolium salts and two Ir(III) complexes were determined by single-crystal X-ray diffraction. Each of the Ir(III) complexes exhibited intense photoluminescence in acetonitrile solution at
room temperature with quantum yields (ϕp) ranging from 42% to 68% and excited-state lifetimes on the order of 2 μs. Voltammetric experiments revealed one formal metal-based oxidation process and two ligand-based reductions for each complex.
All complexes gave moderate to intense annihilation electrochemiluminescence (ECL); however, only the fluorinated complex produced significant coreactant ECL. The combined electrochemical, spectroscopic, and theoretical investigations offer insights into the reasons for this behavior and suggest useful strategies for the design of ECL emitters. A plot of oxidation potential versus emission color is proposed as a convenient reference guide to aid in the prediction of energy sufficiency in ECL reactions.
Item Understanding Electrogenerated Chemiluminescence Efficiency in Blue-Shifted Iridium(III)-Complexes: An Experimental and Theoretical Study(2014-03-14) Francis, Paul S.; Hogan, Conor F.; Barnard, Peter J.; Wilson, David J.; Laird, Sarah; Lopes, Thais; White, Jonathan M.; Donnelly, Paul S.; Connell, Timothy U.; Kerr, Emily; Doeven, Egan H.; Barbante, Gregory J.Compared to tris(2-phenylpyridine)iridium(III) ([Ir(ppy)3]), iridium(III) complexes containing difluorophenylpyridine (df-ppy) and/or an ancillary triazolylpyridine ligand [3-phenyl-1,2,4-triazol-5-ylpyridinato (ptp) or 1-benzyl-1,2,3- triazol-4-ylpyridine (ptb)] exhibit considerable hypsochromic shifts (ca. 25–60 nm), due to the significant stabilising effect of these ligands on the HOMO energy, whilst having relatively little effect on the LUMO. Despite their lower photoluminescence quantum yields compared with [Ir(ppy)3] and [Ir(dfppy) 3], the iridium(III) complexes containing triazolylpyridine ligands gave greater electrogenerated chemiluminescence
(ECL) intensities (using tri-n-propylamine (TPA) as a co-reactant), which can in part be ascribed to the more energetically favourable reactions of the oxidised complex (M+) with both TPA and its neutral radical oxidation product. The calculated iridium(III) complex LUMO energies were shown to be a good predictor of the corresponding M+ LUMO energies, and both HOMO and LUMO levels are related to ECL efficiency.
The theoretical and experimental data together show that the best strategy for the design of efficient new
blue-shifted electrochemiluminophores is to aim to stabilise the HOMO, while only moderately stabilising the LUMO, thereby increasing the energy gap but ensuring favourable thermodynamics and kinetics for the ECL reaction. Of the iridium(III) complexes examined, [Ir(df-ppy)2(ptb)]+ was most attractive as a blue-emitter for ECL detection, featuring a large hypsochromic shift (lmax=454 and 484 nm), superior co-reactant ECL intensity than the archetypal homoleptic green and blue emitters: [Ir(ppy)3] and [Ir(df-ppy)3] (by over 16-fold and threefold, respectively), and greater solubility in polar solvents.