Effects of ZnO nanohexagons and nanorods on the fluorescence behavior of metallophthalocyanines
- Authors: D’Souza, Sarah , Moeno, Sharon , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7263 , http://hdl.handle.net/10962/d1020272
- Description: This paper looks at the fluorescence behavior of zinc phthalocyanines: 2,(3),9(10),16(17),23(24)-tetrakis-(mercaptoacetic acid phthalocyaninato) zinc(II) (ZnTMAAPc), 2,(3),9(10),16(17),23(24)-tetrakis-(mercaptopropanoic acid phthalocyaninato) zinc(II) (ZnTMPAPc) and (OH)AlPcSmix (the latter contains a mixture of the di-, tri- and tetra-sulfonated derivatives with an average of three sulfonated groups per molecule) in the presence of ZnO nanoparticles. Fluorescence lifetimes of Pc complexes generally decreased in the presence of ZnO nanoparticles, with generally longer lifetimes for ZnO nanohexagons compared to ZnO nanorods. , Original publication is available at http://dx.doi.org/10.1016/j.poly.2014.09.012
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Electrocatalytic activity of bimetallic Au–Pd nanoparticles in the presence of cobalt tetraaminophthalocyanine
- Authors: Maringa, Audacity , Mashazi, Philani N , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7245 , http://hdl.handle.net/10962/d1020250
- Description: Au and Pd nanoparticles were individually or together electrodeposited on top of polymerized cobalt tetraaminophthalocyanine (poly-CoTAPc). When Pd and Au nanoparticles are co-deposited together, the electrode is denoted as Au–Pd (co-deposited)/poly-CoTAPc-GCE. X-ray photoelectron spectroscopy (XPS) was used to show the successful deposition of AuNPs, PdNPs and Au–Pd (co-deposited). The scanning electrochemical microscopy showed that Au–Pd (co-deposited)/poly-CoTAPc-GCE (with current range of 9.5–13.5 μA) was more conducting than Au–Pd (co-deposited)-GCE (with current range of 8–12 μA). Electrochemical impedance spectroscopy (EIS) showed that there was less resistance to charge transfer for Au–Pd (co-deposited)/poly-CoTAPc-GCE compared to the rest of the electrodes. Au–Pd (co-deposited)/poly-CoTAPc-GCE showed the best activity for the electrooxidation of hydrazine in terms of limit of detection (0.5 μM), hence shows promise as an electrocatalyst for electrooxidation of hydrazine. , Original publication is available at http://dx.doi.org/10.1016/j.jcis.2014.10.056
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Electrode Modification Using Alkynyl Substituted Fe(II) Phthalocyanine via Electrografting and Click Chemistry for Electrocatalysis
- Authors: Nxele, Siphesihle R , Mashazi, Philani N , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7284 , http://hdl.handle.net/10962/d1020329
- Description: In this work, tetrakis(5-hexyn-oxy)Fe(II) phthalocyanine was synthesised in order to perform a click reaction between the terminal alkyne groups and an azide group on a glassy carbon electrode (GCE) surface. An azide group was formed on the electrode surface following electrografting using 4-azidobenzene diazonium tetrafluoroborate by electrochemical reduction. The Cu(I) catalyzed alkyne-azide Huisgen cycloaddition reaction was then employed in order to react the terminal alkyne groups on the phthalocyanine with the azide groups on the GCE surface. The modified electrode was employed to catalyse the oxidation of hydrazine. The electrode showed good electrocatalytic ability towards the detection of hydrazine with a sensitivity of 15.38 µA mM−1 and a limit of detection of 1.09 µM. , Original publication is available at http://dx.doi.org/10.1002/elan.201500212
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Electrode modification using nanocomposites of electropolymerised cobalt phthalocyanines supported on multiwalled carbon nanotubes
- Authors: Nyoni, Stephen , Mashazi, Philani N , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7293 , http://hdl.handle.net/10962/d1020356
- Description: A polymer of tetra(4)-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninatocobalt(II) (CoPyPc) has been deposited over a multiwalled carbon nanotube (MWCNT) platform and its electrocatalytic properties investigated side by side with polymerized cobalt tetraamino phthalocyanine (CoTAPc). X-ray photoelectron spectroscopy, scanning electron microscopy and cyclic voltammetry studies were used for characterization of the prepared polymers of cobalt phthalocyanine derivatives and their nanocomposites. l-Cysteine was used as a test analyte for the electrocatalytic activity of the nanocomposites of polymerized cobalt phthalocyanines and multiwalled carbon nanotubes. The electrocatalytic activity of both polymerized cobalt phthalocyanines was found to be superior when polymerization was done on top of MWCNTs compared to bare glassy carbon electrode. A higher sensitivity for l-cysteine detection was obtained on CoTAPc compared to CoPyPc. , Original publication is available at http://dx.doi.org/10.1007/s10008-015-2985-6
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Enhanced optical limiting behaviour of indium phthalocyanine derivatives when in solution or embedded in poly(acrylic acid) or poly(methyl methacrylate) polymers
- Authors: Sanusi, Kayode , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7256 , http://hdl.handle.net/10962/d1020265
- Description: The optical limiting performance of indium phthalocyanine-based polymer thin-films with large nonlinear absorption coefficients (βeff) and low limiting threshold intensity (Ilim) are described. The absorption cross-sections and the population dynamics of the excited states are also reported. The excited state absorption cross-sections (σexc) are shown to depend on the transition moment between the T1 and T2 states. βeff values have been shown to be related to the population density of the molecules in the T1 state. The improved optical limiting performance recorded for the investigated phthalocyanine complexes in the presence of polymer matrices has been attributed to the aggregation effects of the complexes in the polymer thin-films. The optical properties of the indium phthalocyanine moieties were found to possess robust sensitivity to a change of the polymer materials. , Original publication available at http://dx.doi.org/10.1016/j.jphotochem.2015.02.003
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Enhanced triplet state parameters for zinc carboxy phenoxy phthalocyanine following conjugation to ascorbic acid: effects of adsorption on single walled carbon nanotubes
- Authors: Ogbodu, Racheal O , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7265 , http://hdl.handle.net/10962/d1020274
- Description: Zinc phthalocyanine bearing four ascorbic acid units (formed via ester bond between zinc carboxy phenoxy phthalocyanines and ascorbic acid) was synthesized and characterized using different spectroscopic methods. The complex (with or without ascorbic acid) was further adsorbed onto single walled carbon nanotubes (SWCNTs) and further characterized using Raman spectroscopy, X-ray diffractometry, transmission electron microscopy and thermogravimetric analysis. The photophysical properties of the complexes were studied. The synthesized complex showed better photophysical properties when compared to the carboxy phenoxy phthalocyanines alone, this is evident in the increase of the triplet quantum yields (ΦT), triplet life-times (τT) and singlet oxygen quantum yields (ΦΔ). The zinc phthalocyanines bearing ascorbic acid showed improved triplet life-times even in the presence of SWCNTs. , Original publication is available at http://dx.doi.org/10.1016/j.poly.2015.01.032
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Enhanced triplet state yields in aqueous media of asymmetric zinc phthalocyanines when conjugated to silver nanoflowers
- Authors: D’Souza, Sarah , George, Reama , Göksel, Meltem , Atilla, Devrim , Durmuş, Mahmut , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7279 , http://hdl.handle.net/10962/d1020315
- Description: Novel low symmetry water-soluble zinc phthalocyanines (ZnPcs, complexes 1 and 2) were synthesized and then mixed with silver nanoflowers. Photophysical and photochemical studies were performed in order to determine the efficiency of complexes 1 and 2 as photosensitizers when alone and when combined with the silver nanoflowers. The Pcs show low fluorescence quantum yields and excellent triplet quantum yields of 0.78 (for 1) and 0.66 (for 2) in aqueous media. The triplet quantum yield values increased to 0.80 and 0.89, respectively, in the presence of silver nanoflowers. Long triplet lifetimes ranging from 180 to 200 μs in DMSO were obtained for complexes 1, 2 and their conjugates with silver nanoflowers. , Original publication is available at http://dx.doi.org/10.1016/j.poly.2015.08.017
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Environmental ethics, protection and valuation
- Authors: Du Preez, M
- Subjects: Environmental ethics , Environmental protection , f-sa
- Language: English
- Type: text , Lectures
- Identifier: http://hdl.handle.net/10948/21022 , vital:29428
- Description: This lecture addresses the environmental ethics, protection and valuation of natural assets. The aim of the lecture is threefold: first, to present a bio-ethical argument for the extension of our moral reference class to include all conscious and non-conscious natural assets; second, to discuss the moral significance of a broader moral reference class in terms of Aldo Leopold’s ‘Land Ethic’; third, to discuss the valuation of natural assets from a system’s perspective with specific reference to the estimation of non-use values. In what follows, Section I discusses environmental protection from a bioethical point of view, Section II discusses the moral significance of a broader moral reference class in terms of Aldo Leopold’s ‘Land Ethic’, Section III describes the concept of valuing natural assets with specific reference to the concept of non-use value and its measurement, and finally, Section IV concludes the lecture.
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Facile synthesis, spectroscopic and electrochemical properties, and theoretical calculations of porphyrin dimers with a bridging amide-bonded xanthene moiety
- Authors: Liang, Xu , Xu, Li , Li, Minzhi , Mack, John , Stone, Justin , Nyokong, Tebello , Jiang, Yu , Kobayashi, Nagao , Zhu, Weihua
- Language: English
- Type: Article
- Identifier: vital:7292 , http://hdl.handle.net/10962/d1020355
- Description: A free base porphyrin dimer bridged by a flexible amide-bonded xanthene moiety and its binuclear zinc(II) complex zinc(II) complex were synthesized and characterized. Structural characterization by MS and 1H NMR spectroscopy confirmed the bridged porphyrin dimer structure. The properties of the dimers were characterized by IR, UV-visible absorption, fluorescence and magnetic circular dichroism (MCD) spectroscopy, and electrochemistry studies. Theoretical calculations were carried out to analyze the electronic structures of porphyrin dimers with a bridging amide-bonded xanthene moiety. , Original publication is available at http://dx.doi.org/10.1142/S1088424615500492
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Fluorescence behavior and singlet oxygen generating abilities of aluminum phthalocyanine in the presence of anisotropic gold nanoparticles
- Authors: Mthethwa, Thandekile , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7258 , http://hdl.handle.net/10962/d1020267
- Description: Gold nanoparticles (spheres, rods and bipyramids) were synthesized. The nanocrystals were characterized by UV–visible spectrometry, transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The as prepared gold nanoparticles were then conjugated to a quaternized 2,(3)-tetra [2-(dimethylamino) ethanethio] substituted Al(OH) phthalocyanine (complex 1). The conjugation of phthalocyanines with gold nanoparticles resulted in a decrease in the fluorescence quantum yields and lifetimes. Conversely, an increase in the singlet oxygen quantum yields was observed for the conjugated complex 1 in the presence of AuNPs. , Original publication is available at http://dx.doi.org/10.1016/j.jlumin.2014.09.005
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Fluorescence Behaviour and Singlet Oxygen Production of Aluminium Phthalocyanine in the Presence of Upconversion Nanoparticles
- Authors: Watkins, Zane , Taylor, Jessica , D’Souza, Sarah , Britton, Jonathan , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7288 , http://hdl.handle.net/10962/d1020337
- Description: NaYF4:Yb/Er/Gd upconversion nanoparticles (UCNP) were synthesised and the photoemission stabilised by embedding them in electrospun fibers. The photophysical behaviour of chloro aluminium tetrasulfo phthalocyanine (ClAlTSPc) was studied in the presence of UCNPs when the two are mixed in solution. The fluorescence quantum yield value of ClAlTSPc decreased in the presence of UCNPs due to the heavy atom effect of UCNPs. This effect also resulted in increase in triplet quantum yields for ClAlTSPc in the presence of UCNPs. The fluorescence lifetimes for UCNPs were shortened at 658 nm in the presence of ClAlTSPc when the former was embedded in fiber and suspended in a dimethyl sulfoxide solution of the latter. A clear singlet oxygen generation by ClAlTSPc though Förster resonance energy transfer was demonstrated using a singlet oxygen quencher, 1,3-diphenylisobenzofuran. , Original publication is available at http://dx.doi.org/10.1007/s10895-015-1632-z
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Fluorescence Behaviour of an Aluminium Octacarboxy Phthalocyanine - NaYGdF4:Yb/Er Nanoparticle Conjugate
- Authors: Taylor, Jessica , Litwinski, Christian , Nyokong, Tebello , Antunes, Edith M
- Language: English
- Type: Article
- Identifier: vital:7247 , http://hdl.handle.net/10962/d1020252
- Description: Using a methanol assisted thermal decomposition approach, sphere shaped NaYGdF4:Yb/Er upconversion nanoparticles (UCNPs) were successfully synthesized. The chemical, spectroscopic and fluorescence properties of the UCNPs were fully characterized. Characteristic upconversion fluorescence emissions were produced by the NPs in the green, red and NIR regions and the NPs were also shown to possess paramagnetic properties. The influence of the UCNPs on the spectroscopic and fluorescence properties of an aluminium octacarboxy phthalocyanine AlOCPc was investigated. Covalent conjugation to an AlOCPc resulted in a large blue shift of the phthalocyanine’s Q band, which was accompanied by a decrease in the Pc’s fluorescence lifetime in DMSO. By combining the phthalocyanine and upconversion nanoparticle, we present a system capable of multimodal imaging, using both the upconversion nanoparticle’s and phthalocyanine’s emission, and magnetic resonance imaging (as a result of doping the upconversion nanoparticles with Gd3+ ions). , Original publication is available at http://dx.doi.org/10.1007/s10895-015-1539-8
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Improved triplet state parameters for indium octacarboxy phthalocyanines when conjugated to quantum dots and magnetite nanoparticles
- Authors: Tshangana, Charmaine , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7252 , http://hdl.handle.net/10962/d1020260
- Description: Fe3O4 magnetic nanoparticles (MNPs) and glutathione (GSH) capped CdSe@ZnS quantum dots (QDs) were separately coordinated to indium octacarboxy phthalocyanine (InPc(COOH)8) to form ClInPc(COOH)8–MNPs and ClInPc(COOH)8–GSH–CdSe@ZnS, respectively. The photophysical parameters (triplet state and fluorescence quantum yields and lifetimes) were determined for the conjugates. The triplet quantum yields increased from ΦT = 0.49 for InPc(COOH)8 alone to ΦT = 0.61 and 0.56 for InPc(COOH)8 in the conjugates: ClInPc(COOH)8–MNPs and ClInPc(COOH)8–GSH–CdSe@ZnS, respectively. The lifetimes also became longer for the conjugates compared to Pc alone. , Original publication is available at http://dx.doi.org/10.1016/j.molstruc.2015.02.040
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Iodine-Doped Cobalt Phthalocyanine Supported on Multiwalled Carbon Nanotubes for Electrocatalysis of Oxygen Reduction Reaction
- Authors: Nyoni, Stephen , Mashazi, Philani N , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7242 , http://hdl.handle.net/10962/d1020246
- Description: 4-(4,6-Diaminopyrimidin-2-ylthio) phthalocyaninatocobalt(II) (CoPyPc) was iodine doped, and its electrocatalytic properties explored. Physical characterization techniques such as UV-vis, X-ray photoelectron, electron paramagnetic resonance and infra-red spectroscopy were used. Cyclic voltammetry, electrochemical impedance spectroscopy and rotating disk electrode were used for electrochemical characterization of electrodes modified with the prepared phthalocyanine and its nanocomposites. The electrocatalytic effect of a new iodine-doped cobalt phthalocyanine derivative supported on multiwalled carbon nanotubes was then investigated towards oxygen reduction reaction. The electrocatalytic activity of the iodine-doped cobalt phthalocyanine was found to be superior in terms of current over the undoped phthalocyanine nanocomposite. , Original publication is available at http://dx.doi.org/10.1002/elan.201400499
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Nanosecond nonlinear optical limiting properties of new trinuclear lanthanide phthalocyanines in solution and as thin films
- Authors: Sekhosana, Kutloano Edward , Amuhaya, Edith , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7267 , http://hdl.handle.net/10962/d1020276
- Description: 2,4,6-Tris[3-thio-9,10,16,17,23,24-hexa(4-tertbutylphenoxy) phthalocyaninato ytterbium (III) chloride]-s-triazin (3) and its lutetium counterpart (4) were synthesized. The nonlinear optical behavior of 3 and 4 were characterized in solution and when embedded in polymer as thin films. Thin films of complexes 3 and 4 in poly(bisphenol A carbonate) showed improved nonlinear optical properties when compared to solution. Complex 3 showed a lower threshold for optical limiting intensity (Ilim) than complex 4, and for phthalocyanines in general. Ilim values were even lower in films compared to solutions. , Original publication is available at http://dx.doi.org/10.1016/j.poly.2014.08.047
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Nonlinear optical behaviour of indium-phthalocyanine tethered to magnetite or silica nanoparticles
- Authors: Sanusi, Kayode , Stone, Justin M. , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7259 , http://hdl.handle.net/10962/d1020268
- Description: Nonlinear absorption and optical limiting properties of indium phthalocyanine (complex 1) tethered to magnetite (SiMNP-1) or silica (SiNP-1) nanoparticles have been investigated using 10 ns pulses at 532 nm laser excitation. The optical limiting behaviours of the nanocomposites and the bare phthalocyanine are compared. Investigation of the triplet state dynamics revealed highly efficient triplet state absorption in the SiMNP-1 dyad. A large nonlinear absorption (βeff) that increased with decrease in the peak input fluence was observed for SiMNP-1. The SiNP-1 composite showed a slight increase in βeff with decreasing peak input fluence. The nonlinear optical data obtained for the SiNP-1 are within the same range of those of the indium phthalocyanine alone. The nanosecond nonlinear absorption and the optical limiting of the nanocomposites are shown to be dominated by a strong excited state absorption from a two-photon pumped state. Nonlinear scattering effects and strong excited state absorption from a two-photon pumped state account for the enhanced optical limiting behaviour of SiMNP-1 relative to the phthalocyanine alone. , Original publication is available at http://dx.doi.org/10.1039/C4NJ01619J
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Nonlinear optical behaviour of indium-phthalocyanine tethered to magnetite or silica nanoparticles.pdf
- Identifier: http://hdl.handle.net/10962/189933 , vital:44948
- Description: Nonlinear absorption and optical limiting properties of indium phthalocyanine (complex 1) tethered to magnetite (SiMNP-1) or silica (SiNP-1) nanoparticles have been investigated using 10 ns pulses at 532 nm laser excitation. The optical limiting behaviours of the nanocomposites and the bare phthalocyanine are compared. Investigation of the triplet state dynamics revealed highly efficient triplet state absorption in the SiMNP-1 dyad. A large nonlinear absorption (βeff) that increased with decrease in the peak input fluence was observed for SiMNP-1. The SiNP-1 composite showed a slight increase in βeff with decreasing peak input fluence. The nonlinear optical data obtained for the SiNP-1 are within the same range of those of the indium phthalocyanine alone. The nanosecond nonlinear absorption and the optical limiting of the nanocomposites are shown to be dominated by a strong excited state absorption from a two-photon pumped state. Nonlinear scattering effects and strong excited state absorption from a two-photon pumped state account for the enhanced optical limiting behaviour of SiMNP-1 relative to the phthalocyanine alone.
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- Date Issued: 2015
Optical properties and electronic structures of axially-ligated group 9 porphyrins
- Authors: Wang, Bei-Bei , Zuo, Huiping , Mack, John , Majumdar, Poulomi , Nyokong, Tebello , Chan, Kin Shing , Shen, Zhen
- Language: English
- Type: Article
- Identifier: vital:7295 , http://hdl.handle.net/10962/d1020358
- Description: A series of group 9 metal tetra-(p-tolyl)-porphyrin (M(ttp), M = Co(II), Rh(III), Ir(III)) complexes with axial phenyl substituents have been synthesized and characterized. An aryl bromide cleavage reaction of transition metal complexes was used to prepare the complexes from Co(ttp), Rh(ttp)Cl and Ir(ttp)COCl, respectively. Magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations have been used to study trends in the optical spectra and electronic structures. The effect of introducing different para-substituents on the phenyl substituents was examined. During fluorescence emission studies, phosphorescence was observed for the Ir(III) complexes in the near infrared (NIR) region. , Original publication is available at http://dx.doi.org/10.1142/S108842461550073X
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Organosilicon compounds as fluorescent chemosensors for fluoride anion recognition
- Authors: Gai, Lizhi , Mack, John , Lu, Hua , Nyokong, Tebello , Li, Zhifang , Kobayashi, Nagao , Shen, Zhen
- Language: English
- Type: Article
- Identifier: vital:7241 , http://hdl.handle.net/10962/d1020245
- Description: Recent developments in organosilicon-based chemosensors for F− recognition are reviewed. The design strategies for improving the photophysical properties of organosilicon-based chemosensors are elaborated, with an emphasis placed on their utility for biological applications. The photophysical properties and electronic structures are analyzed in depth with reference made to the results of molecular modeling calculation and possible future research directions are assessed. , Original publication is available at http://dx.doi.org/10.1016/j.ccr.2014.10.009
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Photocatalytic behaviour of zinc tetraamino phthalocyanine-silver nanoparticles immobilized on chitosan beads
- Authors: Khoza, Phindile , Nyokong, Tebello
- Language: English
- Type: Article
- Identifier: vital:7250 , http://hdl.handle.net/10962/d1020256
- Description: Photocatalytic degradation of Rhodamine 6G using unconjugated zinc tetraamino phthalocyanine (ZnTAPc) or when conjugated to Ag nanoparticles (ZnTAPc–AgNPs) is reported. Upon conjugating ZnTAPc to silver nanoparticles, the singlet oxygen production of the phthalocyanine was slightly increased. ZnTAPc and ZnTAPc–AgNPs were immobilized onto chitosan beads for ease of recovery after photocatalysis. Chitosan beads were characterized by FTIR, XRD and TGA. The photodegradation of Rhodamine 6G was used to evaluate the efficiency of the immobilized photocatalysts. In the presence of AgNPs, the photodegradation of Rhodamine 6G was enhanced. The apparent rates (k) were found to be 8.51 × 10−8 and 1.61 × 10−7 mol L−1 min−1 for chitosan supported ZnTAPc or ZnTAPc–AgNPs, respectively. The observation of good photocatalytic activity of the ZnTAPc when immobilized on chitosan proves the uncompromised efficiency of the photocatalysts even when confined in beads, showing great potential for the functionalized beads as heterogeneous catalysts. , Original publication is available at http://dx.doi.org/10.1016/j.molcata.2015.01.017
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