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Aptamer-based biosensor for prostate specific antigen detection using cobalt phthalocyanine-exfoliated graphite composites

  • Authors: Benise, Emihle
  • Date: 2024-04-04
  • Subjects: Aptamer , Exfoliated graphite nano-platelets , Phthalocyanines , Impedance spectroscopy , Prostate-specific antigen
  • Language: English
  • Type: Academic theses , Master's theses , text
  • Identifier: http://hdl.handle.net/10962/434850 , vital:73110
  • Description: The work focuses on the development of biosensors and their use for the detection of prostate specific antigen (PSA). Four cobalt phthalocyanines (CoPcs) complexes: (1) cobalt tetra pyridyloxy phthalocyanine, (2) cobalt tetra acetamidophenoxy phthalocyanine, (3) cobalt tris(acetamidophenoxy) mono benzoic acid phthalocyanine, and (4) cobalt tris(acetamidophenoxy) mono propionic acid phthalocyanine, an exfoliated graphite (EG), and aptamer are used to make probes for PSA detection. Each complex is π-π stacked onto the EG to form EG-CoPc(π-π) hybrid which was used to modify a glassy carbon electrode (GCE). EG and CoPc were also used to modify the GCE sequential (seq) with CoPc on top to give GCE-EG-CoPc(seq). For the detection PSA, PSA specific aptamer was either sequential added or covalently linked to complexes 3 and 4 on the modified electrodes and was only sequentially added onto complexes 1 and 2 modified electrodes. Electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) were the techniques used for the detection of PSA. The electrodes were found to be selective in bovine serum albumin, glucose and cysteine and stable when 50 DPV scans were run. Electrodes gave good % recovery when human serum was spiked with different PSA concentrations. , Thesis (MSc) -- Faculty of Science, Chemistry, 2024
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  • Date Issued: 2024-04-04

Enhancement of the electrocatalytic activity of phthalocyanines through the reduction in symmetry and conjugation to detonation nanodiamonds

  • Authors: Ncwane, Lunathi
  • Date: 2023-10-13
  • Subjects: Phthalocyanines , Electrocatalysis , Nanodiamonds , Hydrazine
  • Language: English
  • Type: Academic theses , Master's theses , text
  • Identifier: http://hdl.handle.net/10962/424541 , vital:72162
  • Description: This thesis reports on the synthesis of novel phthalocynines tetrakis[(benzo[d]thiazol-2ylthio)phthalocyaninato]cobalt(II)chloride (complex 1) and tris(2-(ethylthio)benzo[d]thiazole)2-(phthalocyanine-9-ylthio)propionate cobalt(II) chloride (complex 2). The complexes are combined with DNDs via different techniques such as π-π stacking, covalent linkage and sequential modification on glassy carbon electrode. The synthesized MPcs and conjugates were characterized using UV-visible, mass, Fourier transform infrared, and Raman spectroscopies as well as transmission electron microscopy and dynamic light scattering. Combining MPcs with DNDs sought to improve electrooxidation of hydrazine. The electrochemical studies were conducted using cyclic voltammetry, chronocoloumetry, electrochemical impedance spectroscopy and chronoamperometry. Hydrazine was utilized as an analyte of interest, due to its mutagenic and carcinogenic effects. Glassy carbon electrodes (GCE) were modified using drop and dry method. The conjugation via covalent linkage proved to be the best way of enhancing electrocatalytic properties. Since it performed better in terms of limit of detection (0.33 μM), even though catalytic rate and sensitivity are not the highest. , Thesis (MSc) -- Faculty of Science, Chemistry, 2023
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  • Date Issued: 2023-10-13

Enhancing the electrocatalytic activity of phthalocyanines through finding the ideal combination of substituents in push-pull phthalocyanine-based systems

  • Authors: Nkhahle, Reitumetse Precious
  • Date: 2023-10-13
  • Subjects: Phthalocyanines , Electrocatalysis , Hydrazine , Nitrites , Activating group , Deactivating group
  • Language: English
  • Type: Academic theses , Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/432578 , vital:72882 , DOI 10.21504/10962/432578
  • Description: Phthalocyanines (Pcs) are a class of synthetic pigments with a similar structure to porphyrins. The work presented in this thesis is centred around these electron-rich macrocycles and their use in electrocatalysis. This body of work provides a more rigorous analysis on asymmetric Pcs, focusing on finding the “ideal” combination of substituents in the synthesis of A3B-type Pcs and how these asymmetric structures compare with their symmetric counterparts (A4) in the electrocatalysis of hydrazine and nitrite. The choice in substituents in the syntheses of the Pcs was such that there is both electron-donating and electron-withdrawing groups to induce a push-pull effect. In the studies involving the electrocatalysis of hydrazine, asymmetric cobalt Pcs (CoPcs) possessing alkyl groups as the primary substituents, with variations in the acid-containing group, along with their symmetric counterparts, probes with potential for further improvement were identified. Using voltammetric and amperometric techniques, the analyte-electrode kinetics, mechanism in which the electrochemical reaction proceeds along with the limits of detection (LoD) were determined. In the general sense, the pentadecylphenoxy-derived CoPcs performed better than those containing the tert-butyl substituent as the dominant substituent with the asymmetric CoPcs producing more favourable results than their symmetric analogues. With respect to the probes designed for nitrite, a multi-dimensional approach was undertaken in that acetaminophen was chosen as the primary substituent whilst multiple changes in the asymmetric component were made. In addition to varying the carboxylic acid-containing substituent, alkyne- and amine-based substituents were also explored in which the alkyne-containing Pc was anchored onto the electrode surface through click chemistry while the amine-bearing Pc was covalently linked (and π-stacked) to nitrogen-doped graphene quantum dots (NGQDs). Another component that was altered was the central metal where CoPcs were compared to manganese Pcs (MnPcs). The most desirable peak oxidation potential for nitrite was observed in the MnPcs as it was the lowest with adsorption sometimes being a better suited method of electrode modification relative to clicking. The inclusion of NGQDs was found to be beneficial when combined with the symmetric CoPc whilst in the presence of an asymmetric Pc complex, less desirable results were observed. Overall, there were variations in the results with the symmetric CoPc sometimes being better than some of the asymmetric CoPcs demonstrating that a blanket-approach in terms of synthesizing and applying asymmetric Pcs is not always viable. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
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  • Date Issued: 2023-10-13

Liposomal formulations of metallophthalocyanines-nanoparticle conjugates for hypoxic photodynamic therapy and photoelectrocatalysis

  • Authors: Nwahara, Nnamdi Ugochinyere
  • Date: 2023-10-13
  • Subjects: Liposomes , Photochemotherapy , Phthalocyanines , Photoelectrochemistry , Cancer Treatment
  • Language: English
  • Type: Academic theses , Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/432159 , vital:72847 , DOI 10.21504/10962/432159
  • Description: This thesis investigates new strategies to enhance the efficacy of photodynamic therapy (PDT) under hypoxic conditions using in-vitro cancer cell models. Phthalocyanines are chosen as viable photosensitizer complexes owing to the favourable absorption properties. To this end, this thesis reports on the synthesis and photophysicochemical properties of various zinc and silicon phthalocyanines (Pcs). To afford better photophysicochemical properties, the reported Pcs were conjugated to different nanoparticles (NPs) through chemisorption as well as amide bond formation to yield Pc-NP conjugates. All the studied Pcs showed relatively high triplet and singlet oxygen quantum yields corresponding to their low fluorescence quantum yields. The various mechanisms for hypoxic response include (i) Type I PDT, (ii) PDT coupled with oxygen-independent therapy and (iii) in-situ oxygen generation using catalase-mimicking nanoparticles which serve to supplement in-vitro oxygen concentrations using MPcs or MPc-NPs conjugates. The mechanisms were assessed using electrochemical, computational techniques and catalase mimicking experiments. The as-synthesised Pcs or Pc-NPs were subjected to liposomal loading before PDT studies which led to enhanced biocompatibility and aqueous dispersity. The in-vitro dark cytotoxicity tests and photodynamic therapy activities of the fabricated Pc-liposomes and Pc-NPs-liposomes on either Henrietta Lacks (HeLa) or Michigan Cancer Foundation-7 (MCF-7) breast cancer cells are presented herein. This work further showed that folic acid (FA) functionalization of liposomes could be exploited for active drug delivery and herein led to an almost 3-fold increase in drug uptake vs non-FA functionalised liposomes in accordance with folate receptor (FR) expression levels between HeLa and MCF-7 cells. The in-vitro dark cytotoxicity and photodynamic therapy of selected Pc complexes and conjugates were accessed using MCF-7 and HeLa cell lines. The various mechanisms; (i) Type I PDT, (ii) PDT coupled with oxygen -independent therapy and (iii) in-situ oxygen generation using catalase-mimicking nanoparticles were shown to adequately compensate for the otherwise attenuation of PDT activity under hypoxia. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
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  • Date Issued: 2023-10-13

Octa carboxy metal (II) phthalocyanine covalent films as pH sensitive electrochemical sensor for neurotransmitters

  • Authors: Moyo, Iphithuli
  • Date: 2023-10-13
  • Subjects: Phthalocyanines , Thin films , Neurotransmitters , Carboxylic acids
  • Language: English
  • Type: Academic theses , Master's theses , text
  • Identifier: http://hdl.handle.net/10962/424525 , vital:72161
  • Description: Octa acyl chloride metallophthalocyanines of cobalt (CoOAClPc) and iron (FeOAClPc) were synthesized and characterized using spectroscopic and electrochemical techniques. The metallophthalocyanines were fabricated as thin films onto phenylethylamine (PEA) pre-grafted Au electrode following a covalent amide reaction. The spectroscopic and electrochemical characterization confirmed the modification of the bare Au with PEA monolayer thin film (Au-PEA) and the covalent immobilization of MOAClPc to yield Au-PEA-MOAClPc (where M is Co and Fe). The acyl chloride functional groups were hydrolyzed forming pH sensitive thin films of terminal carboxylic acid (-COOH) functional groups (Au-PEA-MOCAPc). The Au-PEA-MOCAPc electrode exhibited pH selectivity and sensitivity properties towards the negatively charged [Fe(CN)6]3-/4- and positively charged [Ru(NH3)6]2+/3+ redox probes. The Au-PEA-MOCAPc electrodes were studied for their electrocatalytic and electroanalytical properties towards the detection of catecholamine neurotransmitters; dopamine (DA), epinephrine (EP) and norepinephrine (NOR). The electrodes were further investigated in the screening of ascorbic and uric acids by means of pH sensitive functional groups. The modification process exhibited good reproducibility. Excellent electrocatalytic and electroanalytical properties were observed. The limits of detection (LOD) determined using 3σ/m was found to be 64 nM, 0.22 μM and 0.17 μM for DA, EP and NOR respectively using Au-PEA-CoOCAPc. For Au-PEA-FeOCAPc, the LOD was found to 0.24 μM, 0.45 μM and 0.34 μM for DA, EP and NOR respectively. The Au-PEA-MOCAPc electrodes screened off the strong interferents, ascorbic and uric acid. The Au-PEA-FeOCAPc electrode was evaluated for its potential application in real sample analysis using new born calf serum, and it showed excellent percentage recoveries. , Thesis (MSc) -- Faculty of Science, Chemistry, 2023
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  • Date Issued: 2023-10-13

The electrocatalytic activity of metallophthalocyanines and their conjugates with carbon nanomaterials and metal tungstate nanoparticles

  • Authors: Ndebele, Nobuhle
  • Date: 2023-10-13
  • Subjects: Phthalocyanines , Electrocatalysis , Nitrites , Dopamine , Catechol , Detection limit
  • Language: English
  • Type: Academic theses , Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/431934 , vital:72816 , DOI 10.21504/10962/431933
  • Description: In this dissertation, seventeen phthalocyanine complexes were synthesised. Of these, only four are known and have been published. These complexes were synthesised using the conventional statistical condensation method that involves refluxing the phthalonitrile(s) (4-((1,3-bis(dimethylamino)propan-2-yl)oxy)phthalonitrile, 4-(4-carboxyphenoxy)phthalonitrile, 4-(4-acetylphenoxy)phthalonitrile, dimethyl 5-(3,4-dicyanophenoxy)-isophthalate, 4-(4-(tert-butyl)phenoxy)phthalonitrile, 5-phenoxylpicolinic acid phthalonitrile 4-(4-formylphenoxy) phthalonitrile, and 4-(4-(3-oxo-3-phenylprop-1-enyl) phenoxy) phthalonitrile) with the metal salt and 1,8-diazabicyclo[5.4.0]undecane as a catalyst in a high-temperature solvent. And thereafter (when necessary), isolation and purification of the target compounds were achieved through the use of silica column chromatography. These compounds were characterised using various analytical techniques such as; ultraviolet-visible absorption, mass spectroscopy, and Fourier transform infrared spectra and elemental analysis. These techniques proved that the complexes were successfully synthesised and isolated as pure compounds. Carbon-based (graphene quantum dots and nitrogen-doped graphene quantum dots) and metal oxide (bismuth tungsten oxide and nickel tungsten oxide) nanomaterials were synthesised. Together with the purchased single-walled carbon nanotubes, these nanomaterials were conjugated to some of the MPc complexes via non-covalent (carbon-based nanomaterials) and covalent (metal oxides) linkage forming hybrid materials. These nanomaterials and hybrids were characterised using various analytical methods (ultraviolet-visible absorption, X-ray diffraction, Raman spectroscopy, thermographic analysis, and dynamic light scattering). Nanomaterials were utilised herein to determine their effect on the properties of MPc complexes and provide a synergistic effect in the hope of enhancing these properties. All complexes synthesised in this work (MPcs, nanomaterials and hybrids) were employed as electrocatalysts in electrochemical sensing. These electrocatalysts were embedded onto the glassy carbon electrode via an adsorption method known as drop-casting. The modified electrode surfaces were characterised using cyclic voltammetry, electrochemical impedance spectroscopy and scanning electrochemical microscopy to determine various electrochemical parameters. These electrocatalysts were used in the detection of either nitrite, catechol and/or dopamine. The detection limits, sensitivities, kinetics and catalytic constants were among other parameters determined for each electrocatalyst. These electrocatalysts proved to be stable electrocatalysts that could potentially be used for practical applications. The determined parameters were comparable and sometimes better than those obtained in literature. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
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  • Date Issued: 2023-10-13

The development of ionic zinc(II) phthalocyanines for sono-photodynamic combination therapy of cervical and breast cancer

  • Authors: Nene, Lindokuhle Cindy
  • Date: 2023-03-31
  • Subjects: Phthalocyanines , Sonochemistry , Photochemotherapy , Cancer Treatment
  • Language: English
  • Type: Academic theses , Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/422565 , vital:71958 , DOI 10.21504/10962/422565
  • Description: This study focuses on the development of the sono-photodynamic combination therapy (SPDT) activity of phthalocyanines (Pcs) on the cervical and breast cancer cell lines in vitro. The SPDT technique utilizes ultrasound in combination with light to elicit cytotoxic effects for cancer eradication. In this work, a selection of tetra-peripherally substituted Zn(II) cationic and zwitterionic Pcs were prepared. The photophysical parameters of the Pcs were determined including their fluorescence behaviours and efficiency of the triplet excited state population. The effects of the ultrasonic parameters (frequencies (MHz) and power (W.cm-2)) on the stability of the Pcs were evaluated. Four parameters were evaluated: Par I (1 MHz: 1 W.cm-2), Par II (1 MHz: 2 W.cm-2), Par III (3 MHz: 1 W.cm-2) and Par IV (3 MHz: 2 W.cm-2). The stability of the Pcs reduced with the increase in the ultrasonic power (for Par II and Par IV). The Par I showed the least degradation compared to the other parameters and was therefore used for the SPDT treatments. The sonodynamic (SDT), photodynamic (PDT) therapy activities of the Pcs were studied and compared to their SPDT efficacies. The Pcs showed reactive oxygen species generation during the SDT, PDT and SPDT treatments. For the SDT and SPDT, singlet oxygen (1O2) and hydroxyl radicals (•OH) were detected. For PDT, only the 1O2 were detected. The cell cytotoxicity studies for the Pcs showed relatively higher therapeutic efficacies for the SDT treatments compared to the PDT treatments, where the SPDT showed higher therapeutic efficacies compared to both the SDT and PDT monotreatments on both the cell lines in vitro. Overall, the combination treatments were better compared to the monotreatments. The activities of the Pcs were compared by their differences in structures, including the type of R-group, type of quaternizing agent and type of nanoparticle conjugates. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
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  • Date Issued: 2023-03-31

Dual and targeted photodynamic therapy ablation of bacterial and cancer cells using phthalocyanines and porphyrins in the presence of carbon-based nanomaterials

  • Authors: Openda, Yolande Ikala
  • Date: 2022-10-14
  • Subjects: Phthalocyanines , Porphyrins , Active oxygen , Biofilms , Breast Cancer Treatment , Nanostructured materials , Combination therapy , Photochemotherapy
  • Language: English
  • Type: Academic theses , Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/365945 , vital:65804 , DOI https://doi.org/10.21504/10962//365946
  • Description: Phthalocyanines (Pcs) and porphyrins bearing substituents that possess antibacterial/anticancer properties are used as photosensitizers (PS) for the first time in the work. For targeting specificity and improved photoactivity, the PSs were afterward functionalized with carbon nanomaterials such as graphene quantum dots (GQDs) and detonation nanodiamonds (DNDs) via covalent conjugation (amide or ester bonds) or by non-covalent conjugation (π-π stacking and electrostatic interactions). Furthermore, the PSs-DNDs nanoconjugates were conjugated to either chitosan-capped silver nanoparticles (CSAg) via amide bonds or to the bare silver nanoparticles (Ag NPs) using the silver- nitrogen affinity. The as-synthesized nanoconjugates were also fully characterized by spectroscopic and microscopic methods together with thermal analysis. The potential photocytotoxicity of the complexes alone and their nanoconjugates against S. aureus and/or E. coli planktonic and biofilm cultures has been evaluated in vitro. Compared to the non- quaternized PSs, the cationic analogs exhibited a higher photodynamic inactivation against the planktonic cells with log10 reduction values above 9 in the viable count using a concentration of ca. 1.25 μM following 30 min exposure to light (Light dose: 943 J/cm2 for Pcs and 250 mW/cm2 for porphyrins). Whereas, at a concentration of ca. 100 μM the cationic PSs showed complete eradication of biofilms upon 30 min exposure to light. As a result of conjugation to carbon-based nanomaterials and silver nanoparticles, the compounds proved to be more effective as they exhibited stronger antibacterial and anti-biofilm activities on the multi-drug resistant bacteria strains due to synergetic effect, compared to PSs alone. This suggests that the newly prepared nanohybrids (PS concentration ca. 100 μM) could be used as potential antimicrobial agents in the treatment of biofilm-related infections. The target nanoconjugates showed all the advantages of two different groups existing on a single entity. In light of the potential advantages of combined chemotherapy and photodynamic antimicrobial chemotherapy (PACT), this work reports for the first time the use of PACT-ciprofloxacin (CIP) dual therapy using selected indium quaternized PSs which showed higher photoactivity with complete eradication of both Gram-positive and Gram-negative bacteria biofilms at concentrations of 8 μM of PS versus 2 μg/mL of the antibiotic following 15 min irradiation time (light dose: 471 J/cm2 for Pcs and fluence: 250 mW/cm2 for porphyrins) on S. aureus. Whereas the total killing of E. coli was obtained when combining 8 or 16 μM of PS combined with 4 μg/mL of CIP. The combined treatment resulted in the complete eradication of the matured biofilms with the highest log10 reduction values of 7.05 and 7.20 on S. aureus and E. coli, respectively. Used as a model, positively charged dimethylamino-chalcone Pcs also exhibited interesting photodynamic therapy (PDT) activity against MCF-7 cancer cells giving IC50 values of 17.9 and 7.4 μM, respectively following 15 min irradiation. Additionally, the TD-B3LYP/LanL2DZ calculations were run on the dimethylaminophenyl- porphyrins to compare the singlet excitation energies of quaternized and non-quaternized porphyrins in vacuo. the study shows excellent agreement between time-dependent density- functional theory (TD-DFT) exciting energies and the experimental S1>S0 excitation energies. The small deviation observed between the calculated and experimental spectra arises from the solvent effect. The excitation energies observed in these UV-Vis spectra mostly originated from electron promotion between the highest occupied molecular orbital (HOMO) for the less intense band and the HOMO-1 for the most intense band of the ground states to the lower unoccupied molecular orbital (LUMO) of the excited states. , Thesis (PhD) -- Faculty of Science, Chemistry, 2022
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  • Date Issued: 2022-10-14

Inhibition of aluminium corrosion using phthalocyanines: Experimental and computational studies

  • Authors: Nnaji, Nnaemeka Joshua
  • Date: 2022-04-08
  • Subjects: Aluminum Corrosion , Electrochemistry , Phthalocyanines , Corrosion and anti-corrosives , Protective coatings , Density functionals
  • Language: English
  • Type: Academic theses , Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/294643 , vital:57240 , DOI 10.21504/10962/294643
  • Description: Metal deterioration over time is a process known as corrosion, an electrochemical process, which can occur by surface chemical actions on metals by its environment. Metal corrosion have great economic, security, and environmental consequences, and its control is a major research area in corrosion science. Amongst the different corrosion protecting approaches, the use of corrosion inhibitors and protective coatings have attracted enormous research interest in this area of scholasticism. This has necessitated the computational and electrochemical investigations of aluminium corrosion inhibitive potentials of some compounds in 1M HCl. Metal free (5_H2), ClGa(III) (5_Ga) and Co(II) (5_Co) tetrakis(4-acetamidophenoxy)phthalocyanines as well as Co(II) 2,9,16-tris(4-(tert-butyl)phenoxy)-23-(pyridin-4-yloxy)phthalocyanine (6) and Co(II) 2,9,16,24-tetrakis(4-(tert-butyl)phenoxy)phthalocyanine (7) were synthesized for the first time and studied for corrosion inhibition. The reported ClGa(III) tetrakis(benzo[d]thiazol-2-yl-thio)phthalocyaninine (1), ClGa(III) tetrakis(benzo[d]thiazol-2ylphenoxy)phthalocyanine (2), ClGa(III) tetrakis-4-(hexadecane-1,2-dioxyl)-bis(phthalocyanine) (3) and ClGa(III) tetrakis-4,4′-((4-(benzo[d]thiazol-2-yl)-1,2-bis(phenoxy)-bis(phthalocyanine) (4) were also employed for corrosion inhibition of Al in HCl. Corrosion inhibition measurements using electrochemical techniques showed that increased π conjugation caused (1) to (2) to outperform (1a) and (2a) respectively as aluminium corrosion inhibitors in 1.0 M hydrochloric acid. For similar reason, (4) outperformed 2. (1) and (2) were successfully electrodeposited onto aluminium for corrosion retardation in 1.0 M hydrochloric acid solution. Measurements obtained from electrochemical impedance spectroscopy gave corrosion inhibition efficiency values of 82% for 1 and 86% for 2 in 1.0 M hydrochloric acid solution and showed that electrodeposited phthalocyanines have enhanced aluminium corrosion retardation than when in solution. The use of reduced graphene oxide nanosheets (rGONS) alone as aluminium corrosion inhibitor is discouraged because of poor aluminium corrosion inhibition in 1M HCl. However, synergistic effects were observed when rGONS was mixed each with (4) and (3). (5_H2), (5_Ga) and (5_Co) decreased aluminium corrosion in 1M HCl and observation was that the heavier the atom the more decreased the protection and the free base performed best of the three. Studied tertbutylphenoxy-derived CoPcs (6 and 7) exhibited good aluminium corrosion inhibition properties in studied acidic solution and the unsymmetric CoPc (6) which has more heteroatoms, gave better performance. Quantum chemical calculations involved the use of density functional theoretical (DFT) approaches and gave results which corroborated with experimental findings. , Thesis (PhD) -- Faculty of Science, Chemistry, 2022
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  • Date Issued: 2022-04-08

Singlet oxygen and optical limiting applications of BODIPYs and other molecular dyes

  • Authors: May, Aviwe Khanya
  • Date: 2022-04-08
  • Subjects: Dyes and dyeing Chemistry , Phthalocyanines , Photochemotherapy , Active oxygen , Nonlinear optics , Time-dependent density functional theory , Photochemistry
  • Language: English
  • Type: Academic theses , Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/294618 , vital:57238 , DOI 10.21504/10962/294620
  • Description: A series of structurally diverse novel and previously synthesized BODIPY core dyes are synthesized and characterized in this thesis. These BODIPYs were synthesized using 2-methylpyrrole, 2-ethylpyrrole, 2,4-dimethylpyrrole and 3-ethyl-2,4-dimethylpyrrole as the starting pyrroles. The combination of different pyrroles with the same aldehyde results in BODIPY core dyes that are structural analogues. These core dyes were used as precursors to synthesise halogenated BODIPYs and novel styrylBODIPY dyes, which were successfully characterized using FT-IR and 1H NMR spectroscopy. The halogenated BODIPY core dyes and the styrylBODIPY dyes were also characterized using MALDI-TOF mass spectrometry. The introduction of heavy atoms on the BODIPY core leads to a red shift of the main spectral. In the presence of styryl groups, the main spectral band red shifts to the far red end of the visible region. As expected, the halogenated BODIPY core dyes also had moderate singlet oxygen quantum yields. These halogenated core dyes were found to be suitable as photosensitizers as all the dyes reduced bacterial viability to below 50% during photodynamic antimicrobial chemotherapy (PACT) studies against Staphylococcus aureus. The structure-property relationships studied demonstrate that the presence of protons rather than methyls at the 1,7-positions or iodines at the 2,6-positions results in more favorable PACT activity. This is likely to be related to the greater ability of the meso-aryl to rotate into the plane of the dipyrromethene ligand and suggests that there should be a stronger focus on dyes of this type in future studies in this field. During nonlinear optical (NLO) studies, all the styrylBODIPYs exhibited favorable reverse saturable absorption (RSA) responses. In the absence of methyl groups at the 1,7-positions, the meso-aryl ring lies closer to the π-system of the BODIPY core, enhancing donor (D)–π–acceptor (A) properties and resulting in slightly enhanced optical limiting (OL) parameters. Additionally, there is no evidence that the introduction of heavy atoms at the 2,6-positions significantly enhances OL properties. In a similar manner, alkyl substituents at these positions also do not significantly enhance OL properties; this was studied for the first time using 15 with ethyl groups at the 2,6-positions. The combination of z-scan data and transient spectroscopy for 16 demonstrated that the main mechanism responsible for the NLO properties of nonhalogenated BODIPY dyes is one-photon absorption from the ground state followed by ESA in the singlet manifold. From the NLO studies of 25, OL parameters of 1,3,5-tristyrylBODIPY dyes were found to be similar in magnitude to properties of distyrylBODIPY dyes, but to have less favorable optical properties for OL applications. The OL properties of scandium phthalocyanines were assessed for the first time, since the Sc(III) ion, unusually for a first row transition metal ion, is known to readily form sandwich complexes. The presence of a Sc(III) ion does not significantly enhance the OL properties of phthalocyanines relative to those of rare earth metal ions that also form complexes of this type. Because BODIPYs and phthalocyanines typically absorb significantly in the visible region, transparent PBC polymer thin films of disilane-bridged compounds with minimal absorption in this region were studied and exhibited an excellent RSA response. These compounds may be useful in the design of OL materials that can protect the human eye. The optimized geometries and spectroscopic properties of selected BODIPYs were studied. As expected, the presence of bromine, iodine, ethyl and styryl groups at different positions of the BODIPY core leads to a narrowing of the HOMO–LUMO band gap, which results in a red-shift of the main spectral band. Partial atomic charges have also been calculated for some of the styrylBODIPY dyes studied for application in OL, and electrostatic potential energy maps were also visualized to better assess how the dipole moment of BODIPY dyes can be modulated since this can affect the OL properties. For all the BODIPYs studied, the electronegativity of the atoms present influences charge distribution on the BODIPY structure. , Thesis (PhD) -- Faculty of Science, Chemistry, 2022
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  • Date Issued: 2022-04-08

The systematic assembly of prostate specific antigen electrochemical sensors based on asymmetric Co(II) phthalocyanines, graphitic quantum dots and an aptamer

  • Authors: Nxele, Siphesihle Robin
  • Date: 2022-04-08
  • Subjects: Prostate-specific antigen , Electrochemical sensors , Phthalocyanines , Quantum dots , ‎Co(II) phthalocyanines , Aptamer‎
  • Language: English
  • Type: Doctoral thesis , text
  • Identifier: http://hdl.handle.net/10962/232893 , vital:50035 , DOI 10.21504/10962/232893
  • Description: The need for low-cost, efficient and simple diagnostic tools has led to more research going into this subject, with the aim of making such medical devices more accessible where they are needed. This has led to more researchers developing point-of-care devices for this purpose worldwide, by sensor fabrication. This thesis focuses on electrochemical sensor development for the early diagnosis of prostate cancer. It is common knowledge that prostate cancer is one of the most prevalent carcinomas that have claimed lives due to late diagnosis where even the most invasive treatments have failed. For this reason, development of early detection devices that can even be used in the comfort of home is necessary and quite crucial. Electrochemical sensors have gained much attention due to their ease of fabrication, cost effectiveness, simplicity, ease of use and high efficiency. Using nanocomposites as modifiers has also become popular as they provide greater stability and improve detection limits when used together with biomolecules. With that said, the work reported herein has combined nanocomposites of graphenebased quantum dots, gold nanoparticles, phthalocyanines and an aptamer in order to fabricate aptasensors for the electrochemical detection of prostate cancer biomarker. The aptamer is specifically designed to bind to the biomarker, and the nanocomposites are expected to enhance current output thus lowering detection limits and increasing stability and efficiency. Reproducible results are also expected. Prior to the detection of the prostate cancer biomarker, the quantum dots-phthalocyanine nanohybrids were used to detect L-cysteine, which is an amino acid, in order to verify the synergistic effects as electrode modifiers that lead to the enhancement of current output. This increase in current output is then v exploited for the improvement of aptasensor functionality upon incorporation of the aptamer, for the detection of prostate specific antigen. The research in this thesis has been carried out with the intention of contributing to the world of medical research, more so because of the ever-increasing need for medical care to become accessible to all and not only to those who can afford expensive technologies and treatments. , Thesis (PhD) -- Faculty of Science, Chemistry, 2022
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  • Date Issued: 2022-04-08

Design of pH Sensitive Electrochemical Sensor for Catecholamine Neurotransmitters Detection and the Screening Off of Ascorbic Acid

  • Authors: Tshenkeng, Keamogetse Tebogo Charlotte
  • Date: 2021-10-29
  • Subjects: Catecholamines , Electrochemical sensors , Neurotransmitters , Vitamin C , Cobalt , Phthalocyanines , Cobalt (II) tetra-(3-carboxyphenoxy) phthalocyanine (CoTCPhOPc)
  • Language: English
  • Type: thesis , text
  • Identifier: http://hdl.handle.net/10962/176921 , vital:42772
  • Description: This study presents the synthesis of cobalt (II) tetra-(3-carboxyphenoxy) phthalocyanine (CoTCPhOPc) through the cyclotetramerization of 4-(3-carboxyphe-noxy)phthalonitrile and its full characterization using Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, magnetic circular dichroism (MCD) spectroscopy, elemental analysis and mass spectrometry. The CoTCPhOPc was then immobilized onto phenylethylamino (PEA) pre-grafted gold electrode surface, Au-PEA using amide coupling reaction through a reaction with NHS and DCC to obtain Au-PEA-CoTCPhOPc. This yielded pH sensitive thin films due to the terminal carboxylic acid (–COOH) functional groups. Electrochemical and surface characterization was conducted to confirm the modification of the bare Au with PEA thin film (Au-PEA) and amide coupling of CoTCPhOPc (Au-PEA-CoTCPhOPc). The Au-PEA-CoTCPhOPc electrode was shown to possess pH selective properties towards negatively charged [Fe(CN)6]3-/4- and positively charged [Ru(NH3)6]2+/3+ redox probes. Au-PEA-CoTCPhOPc electrode surface enabled the detection of catecholamine neurotransmitters (dopamine, norepinephrine and epinephrine) and the screening off of ascorbic acid by means of pH sensitive functional groups. Bare Au and Au-PEA electrodes exhibited electro-oxidation and electroreduction of catecholamine neuro-transmitters and ascorbic acid at higher potentials compared to Au-PEA-CoTCPhOPc. There was no electro-oxidation or electroreduction of ascorbic acid at Au-PEA-CoTCPhOPc. For Au-PEA-CoTCPhOPc, excellent electrocatalytic oxidation with the limit of detection (LoD) determined using 3σ was found to be 1.32 (0.95), 2.11 (1.78) and 3.08 μM for electro-oxidation and electroreduction (in brackets) of dopamine, norepinephrine and epinephrine respectively. The limit of quantification (LoQ) was determined using 10σ and found to be 4.41 (3.17), 7.02 (5.93) and 10.3 μM electro-oxidation and electroreduction (in brackets) for dopamine, norepinephrine and epinephrine respectively. The Au-PEA-CoTCPhOPc thin film was shown to screen off ascorbic acid as no electrocatalytic oxidation was observed for up to 100.0 μM concentration. , Thesis (MSc) -- Faculty of Science, Department of Chemistry, 2021
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  • Date Issued: 2021-10-29

Phthalocyanine-nanoparticle conjugates supported on inorganic nanofibers as photocatalysts for the treatment of biological and organic pollutants as well as for hydrogen generation

  • Authors: Mapukata, Sivuyisiwe
  • Date: 2021-10-29
  • Subjects: Phthalocyanines , Nanofibers , Nanoparticles , Zinc , Hydrogen , Organic water pollutants , Water Purification , Electrospinning , Photocatalysis , Photodegradation , Anti-infective agents
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/192831 , vital:45268 , 10.21504/10962/192831
  • Description: This thesis reports on the synthesis, photophysicochemical and photocatalytic properties of various zinc phthalocyanines (Pcs). For enhanced properties and catalyst support, the reported Pcs were conjugated to different nanoparticles (NPs) through chemisorption as well as amide bond formation to yield Pc-NP conjugates. For increased catalyst surface area and catalyst reusability, the Pcs and some of their conjugates were also supported on electrospun inorganic nanofibers i.e. SiO2, hematite (abbreviated Hem and has formula α-Fe2O3), ZnO and TiO2 nanofibers. The effect that the number of charges on a Pc has on its antimicrobial activities was evaluated by comparing the photoactivities of neutral, octacationic and hexadecacationic Pcs against S. aureus, E. coli and C. albicans. The extent of enhancement of their antimicrobial activities upon conjugation (through chemisorption) to Ag NPs was also studied in solution and when supported on SiO2 nanofibers. The results showed that the hexadecacationic complex 3 possessed the best antimicrobial activity against all three microorganisms, in solution and when supported on the SiO2 nanofibers. Covalent conjugation of Pcs with carboxylic acid moieties (complexes 4-6) to amine functionalised NPs (Cys-Ag, NH2-Fe3O4 and Cys-Fe3O4@Ag) resulted in enhanced singlet oxygen generation and thus antibacterial efficiencies. Comparison of the photodegradation efficiencies of semiconductor nanofibers (hematite, ZnO and TiO2) when bare and when modified with a Pc (complex 6) were evaluated. Modification of the nanofibers with the Pc resulted in enhanced photoactivities for the nanofibers with the hematite nanofibers being the best. Modification of the hematite nanofibers with two different Pcs i.e. monosubstituted (complex 5) and an asymmetrical tetrasubstituted Pc (complex 6) showed that complex 6 better enhanced the activity of the nanofibers. Evaluation of the hydrogen generation efficiencies of the bare and modified TiO2 nanofibers calcined at different temperatures demonstrated that the anatase nanofibers calcined at 500 oC possessed the best catalytic efficiency. The efficiency of the TiO2 nanofibers was enhanced in the presence of the Co and Pd NPs as well as a Pc (complex 7), with the extent of enhancement being the greatest for the nanofibers modified with the Pd NPs. The reported findings therefore demonstrate the versatility of applications of Pcs for different water purification techniques when supported on different nanomaterials. , Thesis (PhD) -- Faculty of Science, Chemistry, 2021
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  • Date Issued: 2021-10-29

The construction of phthalocyanine- carbon nanoparticle conjugates for applications in photodynamic therapy and non-linear optics

  • Authors: Matshitse, Refilwe Manyama Stephina
  • Date: 2021-10-29
  • Subjects: Phthalocyanines , Nanodiamonds , Photochemotherapy , Nonlinear optics , Quantum dots
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10962/188397 , vital:44750 , 10.21504/10962/188397
  • Description: The syntheses and characterization of symmetric and asymmetric Pcs functionalized at the peripheral position and sometimes positively charged are reported. The Pcs had either H2, zinc or silicon as central metals and have pyridyloxy, benzothiozole phenoxy, and respective cationic analogues as ring substituents. The Pcs were linked to carbon based nanoparticles such as graphene quantum dots, carbon dots, and detonation nanodiamonds (DNDs) via an ester, amide bond and/or π - π stacking. The physicochemical characteristics of the Pcs were assessed when alone and when in a conjugated system. Both symmetrically and asymmetrically substituted benzothiozole Pcs when quaternised displayed higher triplet and singlet oxygen quantum yields than their unquaternised counterparts. Linkage to carbon nanoparticles (especially to detonation nanodiamonds) had an increasing effect on triplet and singlet oxygen quantum yield. However, a general decrease in singlet oxygen quantum yield on linkage to doped detonation nanodiamonds was associated with the screening effect of DNDs. Heteroatom doped DNDs-Pc nanohybrids have less singlet oxygen than Pcs alone due to molecular structural stability associated with strain that is relatively reduced upon linking Pcs. The In vitro dark cytotoxicity and photodynamic therapy of selected Pc complexes and conjugates against MCF-7 cells was tested. All studied Pc complexes and conjugates showed minimum dark toxicity making them applicable for PDT. When Pc complexes are alone, there is less phototoxicity with >22% cell viability at concentrations ≤ 50 μg/mL relative to conjugates with <22% cell viability at concentrations ≤ 50 μg/mL. There was no direct relationship between PDT and singlet oxygen quantum yields. Nonlinear optical characteristics of complexes was improved upon conjugation of DNDs. Absorbance, input energy, percentage loading, central metal, substituent of Pc and nature of interaction (covalent, noncovalent) are amongst some of the factors that influence nonlinear absorption properties of materials used in this study. All materials followed reverse saturable absorption through two photon absorption mechanism at the excitation wavelength of 532 nm. Aggregates reduce excited state lifetime and Beff under high concentrations/absorbance. A direct relationship between absorbance and Beff of DNDs nanoconjugated systems at low concentrations result in increased optical limiting characteristics of materials. The findings from this work show the importance of linking (nonlinear optics and photodynamic therapy) and doping (photodynamic therapy) photosensitisers such as phthalocyanines and sometimes boron dipyrromethenes onto carbon based nanoparticles for the enhanced characteristics in variable applications. , Thesis (PhD) -- Faculty of Science, Chemistry, 2021
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  • Date Issued: 2021-10-29

Nonlinear optical properties of metal free thio alkyl and tert-butyl phenoxy phthalocyanine

  • Authors: Joseph, Otto
  • Date: 2021-10
  • Subjects: Nonlinear optics , Phthalocyanines , Time-dependent density functional theory , Magnetic circular dichroism , Reverse saturable absorption (RSA) , Real Time Dependent Density Functional Theory (RT-TDDFT)
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10962/190712 , vital:45021
  • Description: This work reports on the nonlinear optical properties of tetra - and octa substituted phthalocyanines (Pcs) utilising pentane thiol and 4-tertbutyl phenol as substituents. Their nonlinear absorption coefficient (𝛽) and absorption cross sections were determined using the Z-scan technique with a 10 ns pulse laser at 532 nm. The molecular second order hyperpolarizability Im[γ] was observed and the following Im[γ] trend was obtained for 𝛼-H2Pc(SC5H11)4 isomers, 5.93 ×10−31 (Cs) 2.24×10−32(D2h) > 1.21×10−32(C4h) > 1.05×10−32 (C2v) esu, respectively, in chloroform. Symmetry was seen to have an effect on the observed reverse saturable absorption (RSA) response. Based on the five level model rate equation nonlinear fit of the RSA response curves and Real Time Time Dependant Density Functional Theory (RT-TDDFT) results, the singlet excited state population dynamics was found to play a significant role in producing the observed Im[γ] trend. , Thesis (MSc) -- Faculty of Science, Chemistry, 2021
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  • Date Issued: 2021-10

Evaluation of metallophthalocyanine functionalized photocatalytic asymmetric polymer membranes for pollution control and antimicrobial activity

  • Authors: Mafukidze, Donovan Musizvinoda Chidyamurimi
  • Date: 2021
  • Subjects: Photosensitizing compounds , Water -- Purification -- Photocatalysis , Phthalocyanines , Polymeric membranes , Porphyrins
  • Language: English
  • Type: text , Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10962/171357 , vital:42052 , 10.21504/10962/171357
  • Description: The conceptualisation of photosensitizing water treatment polymer membranes using phthalocyanine based photosensitizers is reported in this thesis. The key to successful preparation of stable photoactive polymer membranes was established as the covalent anchorage of the photosensitizer to a polymer, which was proven by singlet oxygen generation by the membranes without photosensitizer deterioration. Despite this limitation, the covalent linkage-incapable unsubstituted zinc (II) phthalocyanine (complex 2) was applied as a nanoconjugate of graphene quantum dots (2π(GQDs)). 2π(GQDs) was formed through π-π stacking, and was then covalently anchored, as a proof of concept. This concept was also applied to 2-(4-carboxyphenoxy) phthalocyaninato zinc (II) (complex 3) which is capable of covalent linkage but proved to deteriorate the efficiency of singlet oxygen formation with comparison to the covalent conjugates. Singlet oxygen generation by functionalized polymer membranes rendered them photocatalytic in the degradation of organic pollutants and microorganisms in water. Organic pollutant degradation capability was exemplified by 2π(GQDs) and a porphyrin-phthalocyanine heterodyad (complex 10) functionalized membranes (2π(GQDs)-memb and 10-memb respectively), where a MPc loading of approximately 0.139 μmol MPc/g of membrane was able to achieve a 4-chlorophenol degradation rate of 3.77 × 10−6 mol L−1 min−1 in a second order reaction with an initial 4-chlorophenol concentration of 3.24 × 10−4 mol L−1 for 2π(GQDs)-memb as an example. Antibacterial studies against S.aureus using a quaternized MPc and conjugates of silver triangular nanoprisms with zinc (II) and indium (III) MPcs showed note-worthy improvements in photodynamic antimicrobial chemotherapy (PACT) activity in comparison to the unquaternized MPc precursor, and the free zinc and indium MPcs respectively. Functionalization of polymer membranes with these higher activity photosensitizers translated to the formation of potentially superior biological fouling resistant membranes. The use of porphyrin-phthalocyanine polynuclei arrays (complex 10) in polymer membrane functionalization resulted in the use of a wider wavelength range (white light). The findings from this work as a whole, thus presents the potential applicability of phthalocyanine functionalized polymer membranes in water treatment technology.
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  • Date Issued: 2021

Synthesis, spectroscopic and nonlinear optical properties of asymmetric A3B type phthalocyanine complexes

  • Authors: Mugeza, Rhulani Donney
  • Date: 2021
  • Subjects: Spectrum analysis , Mass spectrometry , Phthalocyanines
  • Language: English
  • Type: text , Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10962/171667 , vital:42108
  • Description: This work reports on the synthesis of symmetrical and asymmetrical A 3 B type metal free, cobalt and zinc Phthalocyanines (Pc) .A wide range of spectroscopic techniques such as Uv - visible absorption (UV), magnetic circular dichroism (MCD), mass spectrometry, elemental analysis, IR spectroscopy and time correlated single photo n counting spectroscopy (TCSPC) have been used to study the spectroscopic properties of the phthalocyanine complexes. The Z - scan technique was used to comparatively investigate the nonlinear absorption coefficient ( 휷 ) and the nonlinear refraction index ( 풏 ퟐ ) of the synthesized complexes. The following trend was obtained for the synthesized Pc’s in terms of the 휷 values 7.25 × 10 − 10 ( 4b ) > 3.76 × 10 − 10 ( 4a ) > 3.52 × 10 − 10 ( 4c ) > 2.29 × 10 − 10 ( 3c ) > 1.68 × 10 − 10 ( 3a ) > 1.65 × 10 − 10 ( 3b ) mW - 1 . The 휷 values trend of synthesized Pc complexes show that the asymmetrical A 3 B type metal free, cobalt and zinc Pc complexes ( 4a , 4b and 4c ) have larger 휷 values as compared to the octa - substituted symmetrical metal free, cobalt and zinc Pc complexes ( 3a , 3b and 3c ) which is attributed to the low symmetry of the Pc complexes. The five - level model rate equations were used to determine the two photon absorption, excited state absorption and ground state absorption cross sections of the synthesized complexes. The z inc A 3 B type asymmetrical Pc complexes gave the largest two photon absorption and 휎 푒 / 휎 푔 ratio values. This Pc complex could be used in future work to enhance the nonlinear response further by introducing nanomaterials and converting the Pc complex to a binuclear Pc. This work also reports on the density functional theory (DFT) calculations o f dipolar/octupolar contributions in order to study the first order hyperpolarizability of the synthesized Pc complexes.
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  • Date Issued: 2021

The electrocatalytic response of metallophthalocyanines when clicked to electrodes and to nanomaterials

  • Authors: Mpeta, Lekhetho Simon
  • Date: 2021
  • Subjects: Phthalocyanines , Nanostructured materials , Electrocatalysis , Nanoparticles , Environmental chemistry , Electrodes , Organic wastes -- Purification
  • Language: English
  • Type: text , Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10962/172191 , vital:42174 , 10.21504/10962/172191
  • Description: Conjugates of nanomaterials and metallophthalocyanines (MPcs) have been prepared and their electrocatalytic activity studied. The prepared nanomaterials are zinc oxide and silver nanoparticles, reduced graphene oxide nanosheets and semiconductor quantum dots. The MPcs used in this work are cobalt (II) (1a), manganese(III) (1b) and iron (II) (1c) 2,9(10),16(17),23(24)- tetrakis 4-((4-ethynylbenzyl) oxy) phthalocyaninato, 2,9(10),16(17),23(24)- tetrakis(5-pentyn-oxy) cobalt (II) phthalocyaninato (2), 9(10),16(17),23(24)- tris-[4-tert-butylphenoxy)-2- (4-ethylbezyl-oxy) cobalt (II) phthalocyaninato (3), 9(10),16(17),23(24)- tris-[4-tertbutylphenoxy)-2-(pent-4yn-yloxy)] cobalt (II) phthalocyaninato (4), cobalt (II) (5a) and manganese (III) (5b) 2,9(10),16(17),23(24)- tetrakis [4-(4-(5-chloro-1H-benzo [d]imidazol-2-yl)phenoxy] phthalocyaninato and 9(10),16(17),23(24)- tris tert butyl phenoxy- 2- [4-(4-(5-chloro-1H-benzo[d]imidazole-2-yl)phenoxy] cobalt (II) phthalocyaninato (6). Some of these MPcs (1a, 3 and 4) were directly clicked on azide grafted electrode, while some (1b, 1c, 2, 5a and 5b) were clicked to azide functionalised nanomaterials and then drop-dried on the electrodes. One phthalocyanine (5b) was drop-dried on the electrode then silver nanoparticles were electrodeposited on it taking advantage of metal-N bond. Scanning electrochemical microscopy, voltammetry, chronoamperometry, electrochemical impedance spectroscopy are among electrochemical methods used to characterise modified electrodes. Transmission electron microscopy, X-ray photoelectron spectroscopy, Xray diffractometry, Raman spectroscopy and infrared spectroscopy were employed to study surface functionalities, morphology and topography of the nanomaterials and complexes. Electrocatalytic activity of the developed materials were studied towards oxidation of 2-mercaptoethanol, hydrazine and hydrogen peroxide while the reduction study was based on oxygen and hydrogen peroxide. In general, the conjugates displayed superior catalytic activity when compared to individual materials. Complex 2 alone and when conjugated to zinc oxide nanoparticles were studied for their nonlinear optical behaviour. And the same materials were explored for their hydrazine detection capability. The aim of this study was to develop sensitive, selective and affordable sensors for selected organic waste pollutants. Conjugates were found to achieve the aim of the study compared to when individual materials were employed.
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  • Date Issued: 2021

Determination of nonlinear optical properties of phthalocyanine regioisomers using computational models

  • Date: 2020
  • Subjects: Electrochemistry , Phthalocyanines , Nanoparticles , Nonlinear optics , Nonlinear optical spectroscopy , Refraction
  • Language: English
  • Type: text , Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10962/166197 , vital:41337
  • Description: This work investigates the effects of the nonlinear optical properties of four different constitutional isomers (C4h, C2v, Cs, and D2h) of a series of tetrasubstituted phthalocyanines (free-base 3-4-tert-butylphenoxyether phthalocyanines, free-base 4-4-tertbutylphenoxyether phthalocyanines, SnCl2 tetra substituted 3-4-tert-butylphenoxyether phthalocyanine, and SnCl2 tetra substituted 4-4-tert-butylphenoxyether phthalocyanine). The properties investigated were the real and imaginary components of the 3rd order hyperpolarizability, as well as the excited state absorption and refraction cross sections. The investigations were performed with a z-scan over a range of laser beam intensities. This work determined the imaginary component of the 3rd order hyperpolarizability for the free-base and SnCl2 3-4-tert-butylphenoxyether phthalocyanines and 4-4-tert-butylphenoxyether phthalocyanines to be highly dependent on the excited state cross sections. The refraction caused due to the real component of the 3rd order hyperpolarizability of the phthalocyanines was also investigated, however, the values found were strongly dependent on the laser beam intensity and the cause of this was investigated. A Five-level model was developed and run on GPGPU computing devices in order to isolate the absorption and refractive cross sections. Theeffects of the regio substitution on the excited state cross sections were also investigated, and the 1st singlet excited state and 1st triplet state absorption cross sections were calculated for all constitutional isomers. It was found that the symmetry of the constitutional isomers have a disproportionately large effect on the excited state absorption when compared to the ground state absorption. The nonlinear refractive properties of all constitutional isomers were also investigated, and the values of the parametric susceptibility are reported herein. The nonlinear refraction was found to have less effect than was seen in the nonlinear absorption. The 1st singlet excited state and 1st triplet state refractive cross sections of all constitutional isomer was determined. The results indicated that if more than one excited state was present and contributing to the nonlinear refraction, then more data than was collected here would be required. However, the 1st singlet excited state cross section were successfully determined for the free-base constitutional isomers. This work concluded that the region substitution affected the excited states more than the ground state.
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  • Date Issued: 2020

Development of graphene materials and phthalocyanines for application in dye-sensitized solar cells

  • Authors: Chindeka, Francis
  • Date: 2020
  • Subjects: Dye-sensitized solar cells , Graphene , Phthalocyanines , Molecular orbitals , Impedance spectroscopy
  • Language: English
  • Type: text , Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10962/166092 , vital:41328
  • Description: Two sets of dye-sensitized solar cells (DSSCs) were fabricated. In the first set, dye-sensitized solar cells (DSSC) were fabricated by incorporating graphene materials as catalysts at the counter electrode. Platinum was also used as a catalyst for comparative purposes. Different phthalocyanines: hydroxyl indium tetracarboxyphenoxy phthalocyanine (1), chloro indium octacarboxy phthalocyanine (2) and dibenzoic acid silicon phthalocyanine (3) were used as dyes. Complex 3 gave the highest power conversion efficiency (η) of 3.19% when using nitrogen doped reduced graphene oxide nanosheets (NrGONS) as a catalyst at the counter electrode, and TiO2 containing rGONS at the anode. The value obtained is close to 3.8% obtained when using Pt catalyst instead of NrGONS at the cathode, thus confirming that NrGONS is a promising candidate to replace the more expensive Pt. The study also shows that placing rGONS on both the anode and cathode improves efficiency. In the second set, DSSCs were fabricated by using 2(3,5-biscarboxyphenoxy), 9(10), 16(17), 23(24)-tri(tertbutyl) phthalocyaninato Cu (4) and Zn (5) complexes as dyes on the ITO-TiO2 photoanodes containing reduced graphene oxide nanosheets (rGONS) or nitrogen-doped rGONS (NrGONS). The evaluation of the assembled DSSCs revealed that using ITO-TiO2-NrGONS-CuPc (4) photoanode had the highest fill factor (FF) and power conversion efficiency (ɳ) of 69 % and 4.36 % respectively. These results show that the asymmetrical phthalocyanine complexes (4) and (5) showed significant improvement on the performance of the DSSC compared to previous work on symmetrical carboxylated phthalocyanines with ɳ = 3.19%.
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  • Date Issued: 2020
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