The influence of gold nanoparticles on the electroactivity of nickel tetrasulfonated phthalocyanine
- Maringa, Audacity, Nyokong, Tebello
- Authors: Maringa, Audacity , Nyokong, Tebello
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189774 , vital:44930 , xlink:href="https://doi.org/10.1142/S1088424614500333"
- Description: We report on the electrodeposition of gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) followed by deposition of nickel tetrasulfonated phthalocyanine (NiTSPc) film by electropolymerization (poly-NiTSPc-GCE) to form Poly-NiTSPc/AuNPs-GCE. The presence of the gold nanoparticles caused a lowering of the anodic and cathodic peak separation (ΔEp) of ferricyanide from 126 mV on poly-NiTSPc to 110 mV on poly-NiTSPc/AuNPs. The electrooxidation of nitrite improved on modified electrodes compared to GCE, with the latter giving Ep = 0.78 V and the modified electrodes gave Ep = 0.62 V or 0.61 V. Poly-NiTSPc/AuNPs-GCE had higher currents compared to poly-NiTSPc-GCE. This indicates the enhancement effect caused by the AuNPs. Electrochemical impedance spectroscopy and chronoamperometric studies also showed that poly-NiTSPc/AuNPs-GCE was a better electrocatalyst than poly-NiTSPc-GCE or AuNPs-GCE.
- Full Text:
- Date Issued: 2014
- Authors: Maringa, Audacity , Nyokong, Tebello
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189774 , vital:44930 , xlink:href="https://doi.org/10.1142/S1088424614500333"
- Description: We report on the electrodeposition of gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) followed by deposition of nickel tetrasulfonated phthalocyanine (NiTSPc) film by electropolymerization (poly-NiTSPc-GCE) to form Poly-NiTSPc/AuNPs-GCE. The presence of the gold nanoparticles caused a lowering of the anodic and cathodic peak separation (ΔEp) of ferricyanide from 126 mV on poly-NiTSPc to 110 mV on poly-NiTSPc/AuNPs. The electrooxidation of nitrite improved on modified electrodes compared to GCE, with the latter giving Ep = 0.78 V and the modified electrodes gave Ep = 0.62 V or 0.61 V. Poly-NiTSPc/AuNPs-GCE had higher currents compared to poly-NiTSPc-GCE. This indicates the enhancement effect caused by the AuNPs. Electrochemical impedance spectroscopy and chronoamperometric studies also showed that poly-NiTSPc/AuNPs-GCE was a better electrocatalyst than poly-NiTSPc-GCE or AuNPs-GCE.
- Full Text:
- Date Issued: 2014
Trends in the TD-DFT calculations of porphyrin and phthalocyanine analogs
- Mack, John, Stone, Justin, Nyokong, Tebello
- Authors: Mack, John , Stone, Justin , Nyokong, Tebello
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193882 , vital:45402 , xlink:href="https://doi.org/10.1142/S108842461450045X"
- Description: In 2005, Kobayashi and coworkers reported trends in the TD-DFT spectra of 17 Zn (II) porphyrinoids [J. Am. Chem. Soc. 2005; 127: 17697] that were analyzed using Michl's perimeter model as part of a study of the anomalous magnetic circular dichroism (MCD) spectroscopy of zinc tetraphenyltetraacenaphthoporphyrin. In recent years, it has become increasingly clear that TD-DFT calculations with the commonly used hybrid B3LYP exchange-correlation functional of the Gaussian software package are problematic in the B-band region of porphyrinoid spectra, since the degree of configurational interaction between the B and higher energy ππ* state appears to be significantly overestimated. The CAM-B3LYP functional is now often preferred for analyzing the optical properties of porphyrinoids, since it includes a long-range correction of the exchange potential, which incorporates an increasing fraction of Hartree–Fock (HF) exchange as the interelectronic separation increases, making it better suited for studying compounds where there is significant charge transfer in the electronic excited states. The trends in the TD-DFT calculations are reexamined with a wider range porphyrinoid compounds including several with pyrazino moieties and are found to provide a closer agreement with the experimental in the B-band region for complexes such as zinc tetraphenylporphyrin and phthalocyanine.
- Full Text:
- Date Issued: 2014
- Authors: Mack, John , Stone, Justin , Nyokong, Tebello
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193882 , vital:45402 , xlink:href="https://doi.org/10.1142/S108842461450045X"
- Description: In 2005, Kobayashi and coworkers reported trends in the TD-DFT spectra of 17 Zn (II) porphyrinoids [J. Am. Chem. Soc. 2005; 127: 17697] that were analyzed using Michl's perimeter model as part of a study of the anomalous magnetic circular dichroism (MCD) spectroscopy of zinc tetraphenyltetraacenaphthoporphyrin. In recent years, it has become increasingly clear that TD-DFT calculations with the commonly used hybrid B3LYP exchange-correlation functional of the Gaussian software package are problematic in the B-band region of porphyrinoid spectra, since the degree of configurational interaction between the B and higher energy ππ* state appears to be significantly overestimated. The CAM-B3LYP functional is now often preferred for analyzing the optical properties of porphyrinoids, since it includes a long-range correction of the exchange potential, which incorporates an increasing fraction of Hartree–Fock (HF) exchange as the interelectronic separation increases, making it better suited for studying compounds where there is significant charge transfer in the electronic excited states. The trends in the TD-DFT calculations are reexamined with a wider range porphyrinoid compounds including several with pyrazino moieties and are found to provide a closer agreement with the experimental in the B-band region for complexes such as zinc tetraphenylporphyrin and phthalocyanine.
- Full Text:
- Date Issued: 2014
Axial coordination of zinc and silicon phthalocyanines to silver and gold nanoparticles: an investigation of their photophysicochemical and antimicrobial behavior
- Masilela, Nkosiphile, Antunes, Edith M, Nyokong, Tebello
- Authors: Masilela, Nkosiphile , Antunes, Edith M , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/241818 , vital:50972 , xlink:href="https://doi.org/10.1142/S1088424613500016"
- Description: This work reports on the axial coordination of zinc phthalocyanine and bis-(1,6-hexanedithiol) silicon phthalocyanine to silver and gold nanoparticles. Red shifting of absorption spectra of the phthalocyanine complexes was observed after conjugation with the nanoparticles. An improvement in the photophysicochemical behavior and antimicrobial activity was achieved in the presence of metal nanoparticles for both complexes. A decrease in triplet lifetimes was observed for all the phthalocyanine metal nanoparticle conjugates. The Zn phthalocyanine complex gave the highest triplet and singlet oxygen quantum yield in the presence of gold nanoparticles. On the other hand, the bacterial inhibition was found to be best for the Si phthalocyanine derivative in the presence of nanoparticles compared to the Zn phthalocyanine counterpart. The highest antimicrobial activity was achieved for both conjugates against B. subtilis compared to S. aureaus both in the dark and under illumination with light.
- Full Text:
- Date Issued: 2013
- Authors: Masilela, Nkosiphile , Antunes, Edith M , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/241818 , vital:50972 , xlink:href="https://doi.org/10.1142/S1088424613500016"
- Description: This work reports on the axial coordination of zinc phthalocyanine and bis-(1,6-hexanedithiol) silicon phthalocyanine to silver and gold nanoparticles. Red shifting of absorption spectra of the phthalocyanine complexes was observed after conjugation with the nanoparticles. An improvement in the photophysicochemical behavior and antimicrobial activity was achieved in the presence of metal nanoparticles for both complexes. A decrease in triplet lifetimes was observed for all the phthalocyanine metal nanoparticle conjugates. The Zn phthalocyanine complex gave the highest triplet and singlet oxygen quantum yield in the presence of gold nanoparticles. On the other hand, the bacterial inhibition was found to be best for the Si phthalocyanine derivative in the presence of nanoparticles compared to the Zn phthalocyanine counterpart. The highest antimicrobial activity was achieved for both conjugates against B. subtilis compared to S. aureaus both in the dark and under illumination with light.
- Full Text:
- Date Issued: 2013
MCD spectroscopy and TD-DFT calculations of a naphthalene-ring-bridged coplanar binuclear phthalocyanine dimer
- Mack, John, Liang, Xu, Dubinina, Tatiana V, Tomilova, Larisa G, Nyokong, Tebello, Kobayashi, Nagao
- Authors: Mack, John , Liang, Xu , Dubinina, Tatiana V , Tomilova, Larisa G , Nyokong, Tebello , Kobayashi, Nagao
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232511 , vital:49998 , xlink:href="https://doi.org/10.1142/S1088424613500259"
- Description: Magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations are used to analyze the electronic structure and optical properties of an alkyl-substituted naphthalene-ring-bridged coplanar binuclear phthalocyanine dimer. An analysis of the MCD spectrum of the naphthalene-ring-bridged dimer relative to those of benzene-bridged compounds reported previously, demonstrates that there is a significantly weaker interaction between the two phthalocyanine rings. TD-DFT results obtained using the B3LYP functional with 6–31G basis sets were found to be problematic. Closer agreement with the experimental data is obtained when the CAM-B3LYP functional is used instead. The naphthalene-ring-bridged compound is found to be unsuitable for use as a photosensitizer for the formation of singlet oxygen, because the ΦT values are negligible.
- Full Text:
- Date Issued: 2013
- Authors: Mack, John , Liang, Xu , Dubinina, Tatiana V , Tomilova, Larisa G , Nyokong, Tebello , Kobayashi, Nagao
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232511 , vital:49998 , xlink:href="https://doi.org/10.1142/S1088424613500259"
- Description: Magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations are used to analyze the electronic structure and optical properties of an alkyl-substituted naphthalene-ring-bridged coplanar binuclear phthalocyanine dimer. An analysis of the MCD spectrum of the naphthalene-ring-bridged dimer relative to those of benzene-bridged compounds reported previously, demonstrates that there is a significantly weaker interaction between the two phthalocyanine rings. TD-DFT results obtained using the B3LYP functional with 6–31G basis sets were found to be problematic. Closer agreement with the experimental data is obtained when the CAM-B3LYP functional is used instead. The naphthalene-ring-bridged compound is found to be unsuitable for use as a photosensitizer for the formation of singlet oxygen, because the ΦT values are negligible.
- Full Text:
- Date Issued: 2013
Nonlinear optical behavior of metal octaphenoxy phthalocyanines
- Sanusi, Sikiru O, Antunes, Edith M, Nyokong, Tebello
- Authors: Sanusi, Sikiru O , Antunes, Edith M , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/241717 , vital:50963 , xlink:href="https://doi.org/10.1142/S1088424613500715"
- Description: In this work, we investigated the nonlinear optical absorption properties of chloroaluminum, chlorogallium, chloroindium, zinc and lead octaphenoxy phthalocyanines in a dimethyl sulphoxide solution using 5 ns pulses at 532 nm. Using the Z-scan technique, the nonlinear optical properties and the excited state absorption cross-sections were determined by fitting the Z-scan data. The k value was the highest for Pb derivative at 211, making it the best nonlinear optical material. In terms of hyperpolarizability, Pb derivative (containing a larger central metal) also gave the largest value followed by aluminum derivative (containing a small central metal). The distortion of the ring caused by the central metal is used to explain the hyperpolarizability values. Large nonlinear absorption coefficient values, βeff, in the range of 3.558–4.763 × 10-9 cm.W-1 and low saturation fluence values, Fsat between 21.5–38.5 mJ.cm-2, were obtained for these samples.
- Full Text:
- Date Issued: 2013
- Authors: Sanusi, Sikiru O , Antunes, Edith M , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/241717 , vital:50963 , xlink:href="https://doi.org/10.1142/S1088424613500715"
- Description: In this work, we investigated the nonlinear optical absorption properties of chloroaluminum, chlorogallium, chloroindium, zinc and lead octaphenoxy phthalocyanines in a dimethyl sulphoxide solution using 5 ns pulses at 532 nm. Using the Z-scan technique, the nonlinear optical properties and the excited state absorption cross-sections were determined by fitting the Z-scan data. The k value was the highest for Pb derivative at 211, making it the best nonlinear optical material. In terms of hyperpolarizability, Pb derivative (containing a larger central metal) also gave the largest value followed by aluminum derivative (containing a small central metal). The distortion of the ring caused by the central metal is used to explain the hyperpolarizability values. Large nonlinear absorption coefficient values, βeff, in the range of 3.558–4.763 × 10-9 cm.W-1 and low saturation fluence values, Fsat between 21.5–38.5 mJ.cm-2, were obtained for these samples.
- Full Text:
- Date Issued: 2013
Third order nonlinear optical properties of phthalocyanines in the presence nanomaterials and in polymer thin films
- Britton, Jonathan, Durmus, Mahmut, Khene, Samson M, Chauke, Vongani, Nyokong, Tebello
- Authors: Britton, Jonathan , Durmus, Mahmut , Khene, Samson M , Chauke, Vongani , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/241772 , vital:50968 , xlink:href="https://doi.org/10.1142/S108842461350003X"
- Description: Third order nonlinear optical properties were determined for phthalocyanine complexes 1–10 containing In, Ga and Zn central metals and tetra- or octa-substituted with benzyloxyphenoxy, phenoxy, tert-butylphenoxy and amino groups at peripheral or non-peripheral positions. The phthalocyanines were embedded in poly (methyl methacrylate) polymer in the presence of CdTe quantum dots. All complexes 1–10 were studied in the presence of CdTe quantum dots and embedded in poly (methyl methacrylate) to form thin films. Complex 3 tetrasubstituted with tert-butylphenoxy groups at non-peripheral positions was also studied in the presence of CdS, CdSe quantum dots, fullerenes, single walled carbon nanotubes. Third order nonlinear optical parameters generally increase for Pcs in the presence of CdTe quantum dots.
- Full Text:
- Date Issued: 2013
- Authors: Britton, Jonathan , Durmus, Mahmut , Khene, Samson M , Chauke, Vongani , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/241772 , vital:50968 , xlink:href="https://doi.org/10.1142/S108842461350003X"
- Description: Third order nonlinear optical properties were determined for phthalocyanine complexes 1–10 containing In, Ga and Zn central metals and tetra- or octa-substituted with benzyloxyphenoxy, phenoxy, tert-butylphenoxy and amino groups at peripheral or non-peripheral positions. The phthalocyanines were embedded in poly (methyl methacrylate) polymer in the presence of CdTe quantum dots. All complexes 1–10 were studied in the presence of CdTe quantum dots and embedded in poly (methyl methacrylate) to form thin films. Complex 3 tetrasubstituted with tert-butylphenoxy groups at non-peripheral positions was also studied in the presence of CdS, CdSe quantum dots, fullerenes, single walled carbon nanotubes. Third order nonlinear optical parameters generally increase for Pcs in the presence of CdTe quantum dots.
- Full Text:
- Date Issued: 2013
Electrocatalytic behavior of cobalt phthalocyanine complexes immobilized on glassy carbon electrode towards the reduction of dicrotophos pesticide
- Vilakazi, Sibulelo, Nyokong, Tebello, Fukuda, Takamitsu, Kobayashi, Nagao
- Authors: Vilakazi, Sibulelo , Nyokong, Tebello , Fukuda, Takamitsu , Kobayashi, Nagao
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245832 , vital:51409 , xlink:href="https://doi.org/10.1142/S1088424612501040"
- Description: Electrocatalytic properties of cobalt phthalocyanine (CoPc), cobalt tetra-carboxy phthalocyanine (CoTCPc) and cobalt octa-carboxy (CoOCPc), towards the detection of dicrotophos have been studied. Catalytic behavior towards the reduction of dicrotophos was found to be dependent on the pH, as well as the substitution on the phthalocyanine ring. Strong electron withdrawing groups on the phthalocyanine ring yielded best catalysis as evidenced by the enhancement of the reduction peak current, (~5 fold) compared to the bare glassy carbon electrode. The analysis gave a good detection limit of 1.25 × 10-7 M, and good linearity for the studied concentration range. A high Tafel slope value was obtained, indicating a strong interaction between dicrotophos and the cobalt phthalocyanine complex.
- Full Text:
- Date Issued: 2012
- Authors: Vilakazi, Sibulelo , Nyokong, Tebello , Fukuda, Takamitsu , Kobayashi, Nagao
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245832 , vital:51409 , xlink:href="https://doi.org/10.1142/S1088424612501040"
- Description: Electrocatalytic properties of cobalt phthalocyanine (CoPc), cobalt tetra-carboxy phthalocyanine (CoTCPc) and cobalt octa-carboxy (CoOCPc), towards the detection of dicrotophos have been studied. Catalytic behavior towards the reduction of dicrotophos was found to be dependent on the pH, as well as the substitution on the phthalocyanine ring. Strong electron withdrawing groups on the phthalocyanine ring yielded best catalysis as evidenced by the enhancement of the reduction peak current, (~5 fold) compared to the bare glassy carbon electrode. The analysis gave a good detection limit of 1.25 × 10-7 M, and good linearity for the studied concentration range. A high Tafel slope value was obtained, indicating a strong interaction between dicrotophos and the cobalt phthalocyanine complex.
- Full Text:
- Date Issued: 2012
Photophysical and photochemical properties of novel phthalocyanines bearing non-peripherally substituted mercaptoquinoline moiety
- Yaşa, Göknur, Erdoğmuş, Ali, Uğur, Ahmet Lütf, Şener, M Kasım, Avcıata, Ulvi, Nyokong, Tebello
- Authors: Yaşa, Göknur , Erdoğmuş, Ali , Uğur, Ahmet Lütf , Şener, M Kasım , Avcıata, Ulvi , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244360 , vital:51250 , xlink:href="https://doi.org/10.1142/S1088424612500940"
- Description: The synthesis, photophysical and photochemical properties of nonperipherally (a) mercaptoquinoline substituted Zn(II), TiO(IV) and Mg(II) and quaternized Zn(II) phthalocyanines are described for the first time. These complexes (2 to 5) and their precursor are characterized by elemental analysis, FT-IR, 1 H NMR, electronic spectroscopy as well as mass spectroscopy. Complexes 2, 4 and 5 have good solubility in organic solvents such as CHCl3, DCM, DMSO, DMF, THF and toluene and are not aggregated in all solvents within a wide concentration range. Complex 3 showed very good solubility in water as well as DMSO and DMF. General trends are described for singlet oxygen, photodegradation and fluorescence quantum yields of these complexes in DMSO and DMF. While complex 2 has higher singlet oxygen and fluorescence quantum yields than 3, 4 and 5, complex 4 has higher fluorescence quantum yields in DMF and DMSO than 2, 3 and 5. The effect of the solvents and metal on the photophysical and photochemical parameters of the metallophthalocyanines are also reported.
- Full Text:
- Date Issued: 2012
- Authors: Yaşa, Göknur , Erdoğmuş, Ali , Uğur, Ahmet Lütf , Şener, M Kasım , Avcıata, Ulvi , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244360 , vital:51250 , xlink:href="https://doi.org/10.1142/S1088424612500940"
- Description: The synthesis, photophysical and photochemical properties of nonperipherally (a) mercaptoquinoline substituted Zn(II), TiO(IV) and Mg(II) and quaternized Zn(II) phthalocyanines are described for the first time. These complexes (2 to 5) and their precursor are characterized by elemental analysis, FT-IR, 1 H NMR, electronic spectroscopy as well as mass spectroscopy. Complexes 2, 4 and 5 have good solubility in organic solvents such as CHCl3, DCM, DMSO, DMF, THF and toluene and are not aggregated in all solvents within a wide concentration range. Complex 3 showed very good solubility in water as well as DMSO and DMF. General trends are described for singlet oxygen, photodegradation and fluorescence quantum yields of these complexes in DMSO and DMF. While complex 2 has higher singlet oxygen and fluorescence quantum yields than 3, 4 and 5, complex 4 has higher fluorescence quantum yields in DMF and DMSO than 2, 3 and 5. The effect of the solvents and metal on the photophysical and photochemical parameters of the metallophthalocyanines are also reported.
- Full Text:
- Date Issued: 2012
Photophysics and photochemistry of octaglucosylated zinc phthalocyanine derivatives
- Iqbal, Zafar, Ogunsipe, Abimbola, Nyokong, Tebello, Lyubimtsev, Alexey, Hanack, Michael, Ziegler, Thomas
- Authors: Iqbal, Zafar , Ogunsipe, Abimbola , Nyokong, Tebello , Lyubimtsev, Alexey , Hanack, Michael , Ziegler, Thomas
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244416 , vital:51255 , xlink:href="https://doi.org/10.1142/S1088424612500630"
- Description: The ground state electronic absorption spectra, photophysics and photochemistry of amphiphilic octaglucosylated zinc phthalocyanines containing oxygen or sulfur bridges are presented. Triplet quantum yield values for the two dyes (in DMF and DMSO) vary between 0.71 and 0.84, while singlet quantum yield values lie between 0.63 and 0.75. Fluorescence lifetimes were determined experimentally by time correlated single photon counting and semi-empirically by fluorescence quenching techniques; and values from both methods were within the same range. Kinetic data were obtained for the quenching of the triplet state of the phthalocyanines by ground state molecular oxygen; the bimolecular collisional quenching rate constant range between 2.35 × 108 and 1.13 × 109 M-1.s-1. These values suggest that triplet states of the dyes are effectively quenched by ground molecular oxygen.
- Full Text:
- Date Issued: 2012
- Authors: Iqbal, Zafar , Ogunsipe, Abimbola , Nyokong, Tebello , Lyubimtsev, Alexey , Hanack, Michael , Ziegler, Thomas
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244416 , vital:51255 , xlink:href="https://doi.org/10.1142/S1088424612500630"
- Description: The ground state electronic absorption spectra, photophysics and photochemistry of amphiphilic octaglucosylated zinc phthalocyanines containing oxygen or sulfur bridges are presented. Triplet quantum yield values for the two dyes (in DMF and DMSO) vary between 0.71 and 0.84, while singlet quantum yield values lie between 0.63 and 0.75. Fluorescence lifetimes were determined experimentally by time correlated single photon counting and semi-empirically by fluorescence quenching techniques; and values from both methods were within the same range. Kinetic data were obtained for the quenching of the triplet state of the phthalocyanines by ground state molecular oxygen; the bimolecular collisional quenching rate constant range between 2.35 × 108 and 1.13 × 109 M-1.s-1. These values suggest that triplet states of the dyes are effectively quenched by ground molecular oxygen.
- Full Text:
- Date Issued: 2012
Schottky barrier diode parameters of Ag/MgPc/p-Si structure
- Canlıca, Mevlüde, Coskun, Mustafa, Altındal, Ahmet, Nyokong, Tebello
- Authors: Canlıca, Mevlüde , Coskun, Mustafa , Altındal, Ahmet , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245820 , vital:51408 , xlink:href="https://doi.org/10.1142/S1088424612500824"
- Description: An Ag/Pc/p-Si Schottky barrier (SB) diode was fabricated. The current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G-V) measurements were carried out to determine the characteristic parameters such as barrier height, ideality factor and series resistance of the SB diode. The non-linear behavior of ln (I) vs. ln (V) and ln (I/V) vs. V1/2 plots indicated that the thermoionic emission theory can be applied to evaluate junction parameters for the investigated SB diode rather than space-charge limited conduction (SCLC) mechanism and bulk-limited Poole–Frenkel emission. The bulk doping concentration NB and fixed oxide charges Nf was determined from the measured high frequency C-V curve and was found to be 9.5 × 1014 cm-3 and 2.3 × 1013 cm-2, respectively. The values of barrier height obtained from Norde's function were compared with those from the forward bias current-voltage characteristic, and it was seen that there was a good agreement between barrier heights from both methods.
- Full Text:
- Date Issued: 2012
- Authors: Canlıca, Mevlüde , Coskun, Mustafa , Altındal, Ahmet , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245820 , vital:51408 , xlink:href="https://doi.org/10.1142/S1088424612500824"
- Description: An Ag/Pc/p-Si Schottky barrier (SB) diode was fabricated. The current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G-V) measurements were carried out to determine the characteristic parameters such as barrier height, ideality factor and series resistance of the SB diode. The non-linear behavior of ln (I) vs. ln (V) and ln (I/V) vs. V1/2 plots indicated that the thermoionic emission theory can be applied to evaluate junction parameters for the investigated SB diode rather than space-charge limited conduction (SCLC) mechanism and bulk-limited Poole–Frenkel emission. The bulk doping concentration NB and fixed oxide charges Nf was determined from the measured high frequency C-V curve and was found to be 9.5 × 1014 cm-3 and 2.3 × 1013 cm-2, respectively. The values of barrier height obtained from Norde's function were compared with those from the forward bias current-voltage characteristic, and it was seen that there was a good agreement between barrier heights from both methods.
- Full Text:
- Date Issued: 2012
Single walled carbon nanotubes functionalized with nickel phthalocyanines
- Khene, Samson, Nyokong, Tebello
- Authors: Khene, Samson , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245843 , vital:51410 , xlink:href="https://doi.org/10.1142/S1088424611004439"
- Description: In this work we report on electrochemical behavior of nickel phthalocyanine derivatives tetrasubstituted peripherally and non-peripherally with hydroxy and used to modify single walled carbon nanotubes. Nickel phthalocyanine complex octasubstituted at the peripheral positions with hydroxy groups was also used to modify single walled carbon nanotubes. Nickel phthalocyanine complex tetrasubstituted with amino groups at peripheral position was covalently and non-covalently linked to single walled carbon nanotubes. All the conjugates of nickel phthalocyanine derivatives with single walled carbon nanotubes were used for the electro oxidation of 4-chlorophenol. The nickel phthalocyanine octabsubstituted with hydroxy groups at the non-peripheral positions gave the best current response and the best resistance against electrode fouling for the oxidation of 4-chlorophenol.
- Full Text:
- Date Issued: 2012
- Authors: Khene, Samson , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245843 , vital:51410 , xlink:href="https://doi.org/10.1142/S1088424611004439"
- Description: In this work we report on electrochemical behavior of nickel phthalocyanine derivatives tetrasubstituted peripherally and non-peripherally with hydroxy and used to modify single walled carbon nanotubes. Nickel phthalocyanine complex octasubstituted at the peripheral positions with hydroxy groups was also used to modify single walled carbon nanotubes. Nickel phthalocyanine complex tetrasubstituted with amino groups at peripheral position was covalently and non-covalently linked to single walled carbon nanotubes. All the conjugates of nickel phthalocyanine derivatives with single walled carbon nanotubes were used for the electro oxidation of 4-chlorophenol. The nickel phthalocyanine octabsubstituted with hydroxy groups at the non-peripheral positions gave the best current response and the best resistance against electrode fouling for the oxidation of 4-chlorophenol.
- Full Text:
- Date Issued: 2012
Synthesis and photophysical properties of covalent conjugates of aqua platinum (II) and octacarboxy-substituted zinc phthalocyanine
- Bulgakov, Roman A, Kuznetsova, Nina A, Dolotova, Olga V, Solovieva, Ludmila I, Mack, John, Chidawanyika, Wadzanai J U, Kaliya, Oleg L, Nyokong, Tebello
- Authors: Bulgakov, Roman A , Kuznetsova, Nina A , Dolotova, Olga V , Solovieva, Ludmila I , Mack, John , Chidawanyika, Wadzanai J U , Kaliya, Oleg L , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/242726 , vital:51073 , xlink:href="https://doi.org/10.1142/S1088424612501209"
- Description: New covalent conjugates of aqua platinum(II) and octacarboxy-substituted zinc phthalocyanine, bearing one, two, three and four aqua platinum moieties on the periphery of the Pc ligand have been synthesized and characterized. The effect of the stepwise introduction of the aqua platinums on the photophysical and photochemical properties of these compounds has been investigated in dimethylsulfoxide solution. It has been found that aqua platinum moieties have only a limited effect on the dynamics of the singlet and triplet excited states, on the ability to sensitize singlet oxygen formation and on the photostability. Each conjugate has a high singlet oxygen quantum yield (ΦΔ 0.51–0.62) and thus retains potential for use as a dual action anticancer drugs by acting as a sensitizer for PDT in addition to the likely chemotherapeutic effects of the Pt(II) complexes.
- Full Text:
- Date Issued: 2012
- Authors: Bulgakov, Roman A , Kuznetsova, Nina A , Dolotova, Olga V , Solovieva, Ludmila I , Mack, John , Chidawanyika, Wadzanai J U , Kaliya, Oleg L , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/242726 , vital:51073 , xlink:href="https://doi.org/10.1142/S1088424612501209"
- Description: New covalent conjugates of aqua platinum(II) and octacarboxy-substituted zinc phthalocyanine, bearing one, two, three and four aqua platinum moieties on the periphery of the Pc ligand have been synthesized and characterized. The effect of the stepwise introduction of the aqua platinums on the photophysical and photochemical properties of these compounds has been investigated in dimethylsulfoxide solution. It has been found that aqua platinum moieties have only a limited effect on the dynamics of the singlet and triplet excited states, on the ability to sensitize singlet oxygen formation and on the photostability. Each conjugate has a high singlet oxygen quantum yield (ΦΔ 0.51–0.62) and thus retains potential for use as a dual action anticancer drugs by acting as a sensitizer for PDT in addition to the likely chemotherapeutic effects of the Pt(II) complexes.
- Full Text:
- Date Issued: 2012
Tetra and octa (2, 6-di-iso-propylphenoxy)-substituted phthalocyanines
- Tuhl, Ahmad, Chidawanayika, Wadzanai J U, Ibrahim, Hamada Mohamed, Al-Awadi, Nouria, Litwinski, Christian, Nyokong, Tebello, Behbehani, Haider, Manaa, Hacene, Makhseed, Saad
- Authors: Tuhl, Ahmad , Chidawanayika, Wadzanai J U , Ibrahim, Hamada Mohamed , Al-Awadi, Nouria , Litwinski, Christian , Nyokong, Tebello , Behbehani, Haider , Manaa, Hacene , Makhseed, Saad
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245855 , vital:51411 , xlink:href="https://doi.org/10.1142/S1088424612004495"
- Description: This work reports on the synthesis of novel metal free, zinc, aluminum, gallium and indium tetra and octa (2,6-di-iso-propylphenoxy)-substituted phthalocyanine derivatives. UV-visible and 1H NMR analyses confirm that a non-planar conformation, adapted by the phenoxy substituents due to steric interaction in both derivative series, perfectly discourage cofacial aggregation. Fluorescence quantum yields vary as a function of the number of substituents on the ring periphery, while the fluorescence lifetimes display no distinct trend. Triplet quantum yields are significantly larger for the tetra 2,6-di-iso-propylphenoxy- substituted derivatives relative to their corresponding octa-substituted species. However there was no overall trend in the triplet lifetime values. For almost all of the phthalocyanine derivatives, singlet oxygen was produced with relatively good quantum yields. This study explores the possibility of fine-tuning their physicochemical properties by simple structural modification.
- Full Text:
- Date Issued: 2012
- Authors: Tuhl, Ahmad , Chidawanayika, Wadzanai J U , Ibrahim, Hamada Mohamed , Al-Awadi, Nouria , Litwinski, Christian , Nyokong, Tebello , Behbehani, Haider , Manaa, Hacene , Makhseed, Saad
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245855 , vital:51411 , xlink:href="https://doi.org/10.1142/S1088424612004495"
- Description: This work reports on the synthesis of novel metal free, zinc, aluminum, gallium and indium tetra and octa (2,6-di-iso-propylphenoxy)-substituted phthalocyanine derivatives. UV-visible and 1H NMR analyses confirm that a non-planar conformation, adapted by the phenoxy substituents due to steric interaction in both derivative series, perfectly discourage cofacial aggregation. Fluorescence quantum yields vary as a function of the number of substituents on the ring periphery, while the fluorescence lifetimes display no distinct trend. Triplet quantum yields are significantly larger for the tetra 2,6-di-iso-propylphenoxy- substituted derivatives relative to their corresponding octa-substituted species. However there was no overall trend in the triplet lifetime values. For almost all of the phthalocyanine derivatives, singlet oxygen was produced with relatively good quantum yields. This study explores the possibility of fine-tuning their physicochemical properties by simple structural modification.
- Full Text:
- Date Issued: 2012
The synthesis, photophysical and dielectric properties of ball-type dinuclear zinc phthalocyanine
- Canlıca, Mevlüde, Altındal, Ahmet, Nyokong, Tebello
- Authors: Canlıca, Mevlüde , Altındal, Ahmet , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/243532 , vital:51161 , xlink:href="https://doi.org/10.1142/S1088424612500836"
- Description: The synthesis of ball-type dinuclear Zn(II) phthalocyanine containing four 4,4′-(9H-fluorene-9,9-diyl)diphenol substituents at the non-peripheral position is presented. The structure of the synthesized compound was characterized using elemental analyzes, and UV-vis, FT-IR, 1H NMR and mass spectroscopies. The ΦF value was 0.16 and ΦT value was 0.72. The complex showed reasonably long triplet lifetimes with τT 7210 μs in DMSO. The frequency and temperature dependence of the dielectric properties of ZnPc were also investigated in the frequency range of 40–105 Hz and in the temperature range of 300–440 °K. It has been observed that both dielectric constant ε′ and dielectric loss ε″ decrease with the rise in frequency as they increase with the rise in temperature. The decrease in ε′ with increasing frequency is attributed to the fact that as the frequency increases, the polarizability contribution from orientation sources decreases and finally disappears.
- Full Text:
- Date Issued: 2012
- Authors: Canlıca, Mevlüde , Altındal, Ahmet , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/243532 , vital:51161 , xlink:href="https://doi.org/10.1142/S1088424612500836"
- Description: The synthesis of ball-type dinuclear Zn(II) phthalocyanine containing four 4,4′-(9H-fluorene-9,9-diyl)diphenol substituents at the non-peripheral position is presented. The structure of the synthesized compound was characterized using elemental analyzes, and UV-vis, FT-IR, 1H NMR and mass spectroscopies. The ΦF value was 0.16 and ΦT value was 0.72. The complex showed reasonably long triplet lifetimes with τT 7210 μs in DMSO. The frequency and temperature dependence of the dielectric properties of ZnPc were also investigated in the frequency range of 40–105 Hz and in the temperature range of 300–440 °K. It has been observed that both dielectric constant ε′ and dielectric loss ε″ decrease with the rise in frequency as they increase with the rise in temperature. The decrease in ε′ with increasing frequency is attributed to the fact that as the frequency increases, the polarizability contribution from orientation sources decreases and finally disappears.
- Full Text:
- Date Issued: 2012
Optical limiting behavior of ring substituted zinc, indium and gallium phthalocyanines in the presence of quantum dots
- Britton, Jonathan, Litwinski, Christian, Durmus, Mahmut, Chauke, Vongani, Nyokong, Tebello
- Authors: Britton, Jonathan , Litwinski, Christian , Durmus, Mahmut , Chauke, Vongani , Nyokong, Tebello
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/247122 , vital:51548 , xlink:href="https://doi.org/10.1142/S1088424611004142"
- Description: This paper presents the study of the effects of CdTe-TGA quantum dots (QDs) on optical limiting ability of different phthalocyanine (Pc) complexes (1–10) containing Zn, Ga, In central metals and substituted with benzyloxyphenoxy, phenoxy, tert-butylphenoxy and amino groups. The optical limiting parameters of Pcs were higher for tert-butylphenoxy when compared to benzyloxyphenoxy and phenoxy substituents, in DMSO. Non-peripheral substitution decreased the optical limiting parameters. Third-order susceptibility (Im[χ(3)]/α) values of Pcs in the absence and presence of CdTe QDs were in the 10-12 to 10-10 esu.cm range. Hyperpolarizabilities (γ) ranged from 10-31 to 10-29 esu L for Pc alone or in mixture with QDs. There is a general improvement in optical limiting ability of Pc complexes in the presence of CdTe TGA QDs. Due to these promising results, future work can be implemented for the creation of Pc:QD thin films, which would then be examined to ensure that their optical limiting ability is still acceptable.
- Full Text:
- Date Issued: 2011
- Authors: Britton, Jonathan , Litwinski, Christian , Durmus, Mahmut , Chauke, Vongani , Nyokong, Tebello
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/247122 , vital:51548 , xlink:href="https://doi.org/10.1142/S1088424611004142"
- Description: This paper presents the study of the effects of CdTe-TGA quantum dots (QDs) on optical limiting ability of different phthalocyanine (Pc) complexes (1–10) containing Zn, Ga, In central metals and substituted with benzyloxyphenoxy, phenoxy, tert-butylphenoxy and amino groups. The optical limiting parameters of Pcs were higher for tert-butylphenoxy when compared to benzyloxyphenoxy and phenoxy substituents, in DMSO. Non-peripheral substitution decreased the optical limiting parameters. Third-order susceptibility (Im[χ(3)]/α) values of Pcs in the absence and presence of CdTe QDs were in the 10-12 to 10-10 esu.cm range. Hyperpolarizabilities (γ) ranged from 10-31 to 10-29 esu L for Pc alone or in mixture with QDs. There is a general improvement in optical limiting ability of Pc complexes in the presence of CdTe TGA QDs. Due to these promising results, future work can be implemented for the creation of Pc:QD thin films, which would then be examined to ensure that their optical limiting ability is still acceptable.
- Full Text:
- Date Issued: 2011
Applications of polymerized metal tetra-amino phthalocyanines towards hydrogen peroxide detection
- Mashazi, Philani N, Togo, Chumunorwa, Limson, Janice L, Nyokong, Tebello
- Authors: Mashazi, Philani N , Togo, Chumunorwa , Limson, Janice L , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/261840 , vital:53451 , xlink:href="https://doi.org/10.1142/S1088424610001994"
- Description: This work reports the use of metallo tetra-amino phthalocyanines (MTAPc, M = Co and Mn) polymer thin films on gold and glassy carbon electrode surfaces for the detection and monitoring of hydrogen peroxide (H2O2). The polymer-modified electrodes were characterized using electrochemical and microscopic-based methods. Atomic force microscopy (AFM) was used to study the bare and polymer-modified ITO surfaces. The electrocatalytic reduction of H2O2 with glassy carbon polymer-modified electrodes gave higher current densities compared to their gold counterparts. The electroanalytical properties of H2O2 were obtained using a real-time calibration curve of the amperometric determination in pH 7.4 aqueous solution. The limits of detection (LoD) of the polymer-modified electrodes towards electroreduction of H2O2 were of the order of 10–7 M, with high sensitivity ranging from 6.0–15.4 mA.mM-1.cm-2.
- Full Text:
- Date Issued: 2010
- Authors: Mashazi, Philani N , Togo, Chumunorwa , Limson, Janice L , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/261840 , vital:53451 , xlink:href="https://doi.org/10.1142/S1088424610001994"
- Description: This work reports the use of metallo tetra-amino phthalocyanines (MTAPc, M = Co and Mn) polymer thin films on gold and glassy carbon electrode surfaces for the detection and monitoring of hydrogen peroxide (H2O2). The polymer-modified electrodes were characterized using electrochemical and microscopic-based methods. Atomic force microscopy (AFM) was used to study the bare and polymer-modified ITO surfaces. The electrocatalytic reduction of H2O2 with glassy carbon polymer-modified electrodes gave higher current densities compared to their gold counterparts. The electroanalytical properties of H2O2 were obtained using a real-time calibration curve of the amperometric determination in pH 7.4 aqueous solution. The limits of detection (LoD) of the polymer-modified electrodes towards electroreduction of H2O2 were of the order of 10–7 M, with high sensitivity ranging from 6.0–15.4 mA.mM-1.cm-2.
- Full Text:
- Date Issued: 2010
Electrochemical, spectroscopic and microscopic studies of new manganese phthalocyanine complexes in solution and as self-assembled monolayers on gold
- Coates, Megan, Antunes, Edith M, Nyokong, Tebello
- Authors: Coates, Megan , Antunes, Edith M , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/261144 , vital:53363 , xlink:href="https://doi.org/10.1142/S1088424610002471"
- Description: Four new manganese(III) phthalocyanines (3a–d), octasubstituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups, respectively, were synthesized. Their specific electrochemical, spectroscopic and microscopic properties in solution and as self-assembled monolayers on gold were characterized. The UV-vis spectra confirmed red-shifted Q bands for all the complexes, due to the effect of the central metal and the electron-donating substituents. Three redox couples were visible during cyclic voltammetry studies for the four complexes, and spectroelectrochemistry confirmed the couples as corresponding to MnIIIPc-2/MnIIPc-2 (II) (metal reduction), MnIIPc-2/MnIIPc-3 (III) (ring reduction) and MnIIIPc-1/MnIIIPc-2 (I) (ring oxidation). Electrochemistry was also used to determine the blocking characteristics of the MnPc self-assembled monolayers on gold, which proved to be highly dependent on the type of substituent. Other methods of characterization included Raman spectroscopy, atomic force and scanning electrochemical microscopy analyses of the SAMs.
- Full Text:
- Date Issued: 2010
- Authors: Coates, Megan , Antunes, Edith M , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/261144 , vital:53363 , xlink:href="https://doi.org/10.1142/S1088424610002471"
- Description: Four new manganese(III) phthalocyanines (3a–d), octasubstituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups, respectively, were synthesized. Their specific electrochemical, spectroscopic and microscopic properties in solution and as self-assembled monolayers on gold were characterized. The UV-vis spectra confirmed red-shifted Q bands for all the complexes, due to the effect of the central metal and the electron-donating substituents. Three redox couples were visible during cyclic voltammetry studies for the four complexes, and spectroelectrochemistry confirmed the couples as corresponding to MnIIIPc-2/MnIIPc-2 (II) (metal reduction), MnIIPc-2/MnIIPc-3 (III) (ring reduction) and MnIIIPc-1/MnIIIPc-2 (I) (ring oxidation). Electrochemistry was also used to determine the blocking characteristics of the MnPc self-assembled monolayers on gold, which proved to be highly dependent on the type of substituent. Other methods of characterization included Raman spectroscopy, atomic force and scanning electrochemical microscopy analyses of the SAMs.
- Full Text:
- Date Issued: 2010
Photoelectrochemical characterization of electrodeposited ZnO thin films sensitized by octacarboxymetallophthalocyanine derivatives
- Idowu, Mopelola, Loewenstein, Thomas, Hastall, Andreas, Nyokong, Tebello, Schlettwein, Derck
- Authors: Idowu, Mopelola , Loewenstein, Thomas , Hastall, Andreas , Nyokong, Tebello , Schlettwein, Derck
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/262655 , vital:53541 , xlink:href="https://doi.org/10.1142/S1088424610001854"
- Description: Hybrid thin films of crystalline zinc oxide (ZnO) modified by different octacarboxymetallophthalocyanines (MOCPc) were prepared by the readsorption method. Homogeneously blue or green thin films were formed. The photoelectrochemical characteristics of the electrodes were studied by time-resolved photocurrent measurements. Zinc(II) 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine (ZnOCPc) showed considerably large quantum efficiency in sensitization of ZnO, one of the highest quantum efficiencies obtained so far with phthalocyanine-type sensitizers on nanocrystalline ZnO films.
- Full Text:
- Date Issued: 2010
- Authors: Idowu, Mopelola , Loewenstein, Thomas , Hastall, Andreas , Nyokong, Tebello , Schlettwein, Derck
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/262655 , vital:53541 , xlink:href="https://doi.org/10.1142/S1088424610001854"
- Description: Hybrid thin films of crystalline zinc oxide (ZnO) modified by different octacarboxymetallophthalocyanines (MOCPc) were prepared by the readsorption method. Homogeneously blue or green thin films were formed. The photoelectrochemical characteristics of the electrodes were studied by time-resolved photocurrent measurements. Zinc(II) 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine (ZnOCPc) showed considerably large quantum efficiency in sensitization of ZnO, one of the highest quantum efficiencies obtained so far with phthalocyanine-type sensitizers on nanocrystalline ZnO films.
- Full Text:
- Date Issued: 2010
Probing electrochemical and electrocatalytic properties of cobalt (II) and manganese (III) octakis (hexylthio) phthalocyanine as self-assembled monolayers
- Mashazi, Philani N, Antunes, Edith M, Nyokong, Tebello
- Authors: Mashazi, Philani N , Antunes, Edith M , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/249115 , vital:51779 , xlink:href="https://doi.org/10.1142/S108842461000277X"
- Description: New peripherally (β) and non-peripherally (α) substituted metal octakis(hexylthio)phthalocyanines (β- and α-MOcHexTPc) containing cobalt and manganese as metal centers were synthesized. Their characterization using electrochemical methods showed that these complexes exhibit several redox processes at E1/2 (mV vs. Ag∣AgCl) = 380 (212) (I), 1140 (864) (II), -450 (-460) (III) and -1170 (-1304) (IV) for β- (α-) CoOcHexTPc. These redox processes were assigned to CoIIIPc-2/CoIIPc-2 (I), CoIIIPc-1/CoIIIPc-2 (II), CoIIPc-2/CoIPc-2 (III) and CoIPc-2/CoIPc-3 (IV) using spectroelectrochemistry. For the β- (α-) MnOcHexTPc complex the redox processes were observed at E1/2 (mV vs. Ag∣AgCl) = -20 (5) (I), -530 (-640) (II) and -1270 (-1380) (III) and were assigned to MnIIIPc-2/MnIIPc-2 (I), MnIIPc-2/MnIIPc-3 (II) and MnIIPc-3/MnIIPc-4 (III). Electrochemical and microscopic characterization using AFM showed that the self-assembled monolayers (SAMs) are formed on the gold surface using these complexes. The electrochemical characterization showed the blocking of the Faradaic processes at SAMs modified electrodes and these reactions are well-known to easily occur at unmodified gold electrodes. The AFM characterization showed an increase in surface roughness upon modifying the gold surface with MOcHexTPc SAMs, further confirming the presence of the monolayers on the gold surface. The MOcHexTPc SAMs were investigated for their electrocatalytic application towards H2O2 detection. The MOcHexTPc SAMs modified gold electrodes gave excellent currents for H2O2 detection. The observed H2O2 electrocatalytic reduction peaks were close to where the metal redox processes from the MOcHexTPc occurred, showing the involvement of the metal redox processes in the electrocatalytic mediation reactions.
- Full Text:
- Date Issued: 2010
- Authors: Mashazi, Philani N , Antunes, Edith M , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/249115 , vital:51779 , xlink:href="https://doi.org/10.1142/S108842461000277X"
- Description: New peripherally (β) and non-peripherally (α) substituted metal octakis(hexylthio)phthalocyanines (β- and α-MOcHexTPc) containing cobalt and manganese as metal centers were synthesized. Their characterization using electrochemical methods showed that these complexes exhibit several redox processes at E1/2 (mV vs. Ag∣AgCl) = 380 (212) (I), 1140 (864) (II), -450 (-460) (III) and -1170 (-1304) (IV) for β- (α-) CoOcHexTPc. These redox processes were assigned to CoIIIPc-2/CoIIPc-2 (I), CoIIIPc-1/CoIIIPc-2 (II), CoIIPc-2/CoIPc-2 (III) and CoIPc-2/CoIPc-3 (IV) using spectroelectrochemistry. For the β- (α-) MnOcHexTPc complex the redox processes were observed at E1/2 (mV vs. Ag∣AgCl) = -20 (5) (I), -530 (-640) (II) and -1270 (-1380) (III) and were assigned to MnIIIPc-2/MnIIPc-2 (I), MnIIPc-2/MnIIPc-3 (II) and MnIIPc-3/MnIIPc-4 (III). Electrochemical and microscopic characterization using AFM showed that the self-assembled monolayers (SAMs) are formed on the gold surface using these complexes. The electrochemical characterization showed the blocking of the Faradaic processes at SAMs modified electrodes and these reactions are well-known to easily occur at unmodified gold electrodes. The AFM characterization showed an increase in surface roughness upon modifying the gold surface with MOcHexTPc SAMs, further confirming the presence of the monolayers on the gold surface. The MOcHexTPc SAMs were investigated for their electrocatalytic application towards H2O2 detection. The MOcHexTPc SAMs modified gold electrodes gave excellent currents for H2O2 detection. The observed H2O2 electrocatalytic reduction peaks were close to where the metal redox processes from the MOcHexTPc occurred, showing the involvement of the metal redox processes in the electrocatalytic mediation reactions.
- Full Text:
- Date Issued: 2010
Symmetrically and unsymmetrically substituted carboxy phthalocyanines as sensitizers for nanoporous ZnO films
- Masilela, Nkosiphile, Nombona, Nolwazi, Loewenstein, Thomas, Nyokong, Tebello, Schlettwein, Derck
- Authors: Masilela, Nkosiphile , Nombona, Nolwazi , Loewenstein, Thomas , Nyokong, Tebello , Schlettwein, Derck
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/249126 , vital:51780 , xlink:href="https://doi.org/10.1142/S1088424610002793"
- Description: The photoelectroectrochemical studies of water soluble octacarboxylated oxotitanium (OTiOCPc), zinc (ZnOCPC), hydroxyaluminium ((OH)AlOCPc), dihydroxysilicon ((OH)2SiOCPc), hydroxygallium (OHGaOCPc) and low symmetry zinc monocarboxy (ZnMCPc) phthalocyanines were performed. The dyes were adsorbed to nanoporous ZnO electrodeposited in the presence of eosin Y as structure directing agent (SDA) on FTO substrates by refluxing or soaking the films in a solution containing the dye of interest such that a full surface coverage was achieved. High external (IPCE) and internal (APCE) quantum efficiencies of up to 50.6% and 96.7% were achieved for the OTiOCPc complex. There was a lower overall cell efficiency for cells sensitized with phthalocyanines containing hydroxyl as axial ligand ZnO/(OH)2SiOCPc, ZnO/(OH)GaOCPc and (OH)AlOCPc because of strong aggregation on the surface of the electrodes. To further suppress dye aggregation, the zinc complex of a new monocarboxylated phthalocyanine sensitizer with bulky naphtho side groups (ZnMCPc) was employed. Among the studied sensitizers, ZnMCPc gave the highest overall cell efficiency of phthalocyanine electrodeposited on ZnO of η = 0.48%.
- Full Text:
- Date Issued: 2010
- Authors: Masilela, Nkosiphile , Nombona, Nolwazi , Loewenstein, Thomas , Nyokong, Tebello , Schlettwein, Derck
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/249126 , vital:51780 , xlink:href="https://doi.org/10.1142/S1088424610002793"
- Description: The photoelectroectrochemical studies of water soluble octacarboxylated oxotitanium (OTiOCPc), zinc (ZnOCPC), hydroxyaluminium ((OH)AlOCPc), dihydroxysilicon ((OH)2SiOCPc), hydroxygallium (OHGaOCPc) and low symmetry zinc monocarboxy (ZnMCPc) phthalocyanines were performed. The dyes were adsorbed to nanoporous ZnO electrodeposited in the presence of eosin Y as structure directing agent (SDA) on FTO substrates by refluxing or soaking the films in a solution containing the dye of interest such that a full surface coverage was achieved. High external (IPCE) and internal (APCE) quantum efficiencies of up to 50.6% and 96.7% were achieved for the OTiOCPc complex. There was a lower overall cell efficiency for cells sensitized with phthalocyanines containing hydroxyl as axial ligand ZnO/(OH)2SiOCPc, ZnO/(OH)GaOCPc and (OH)AlOCPc because of strong aggregation on the surface of the electrodes. To further suppress dye aggregation, the zinc complex of a new monocarboxylated phthalocyanine sensitizer with bulky naphtho side groups (ZnMCPc) was employed. Among the studied sensitizers, ZnMCPc gave the highest overall cell efficiency of phthalocyanine electrodeposited on ZnO of η = 0.48%.
- Full Text:
- Date Issued: 2010