Browsing by Subject "Conjugated polymers."

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Open Access
Conjugated polymer nanoparticles for biomedical applications including bioimaging and drug delivery
(2013) Ünal, Özlem
Open Access
Conjugated polymers based on polyfluorene derivatives and polypyrrole
(2007) Koldemir, Ünsal
In this thesis, a series of polyfluorene based copolymers have been prepared via Suzuki Coupling for use in light emitting diodes (LEDs). Polyfluorene based polymers are synthesized from different monomers. These polymers are characterized with spectroscopic techniques including FT-IR, UV-VIS, Fluorescence and 1H, 13C NMR. Conjugated polymers are attractive chemical structures inherently allowing charge transport. However, in the solid state, conjugated polymers lack stability and form aggregates. To overcome this problem, conjugated polymers can be converted to insulated molecular wires. This can be achieved by separation of the conjugated polymer chains by a macrocycle. In this study, encapsulation of conjugated polymers is tried with two methods. First method is to encapsulate the polymer main chain by macrocycles. Polypyrrole based polypseudorotaxane is prepared in this way. Pyrrole is complexed with the cucurbit[6]uril (CB(6)) and following chemical oxidation by FeCl3 in acidic medium yields the desired polypseudorotaxane. Spectroscopic investigations such as FT-IR, UV-VIS, Fluorescence and 1H-NMR confirm the formation of polypyrrole based polypseudorotaxane. The second method involves the rotaxanation of the polymer side chains. For this purpose, fluorene based monomers are chosen because the 9th position of fluorene can be easily functionalized. After attaching suitable groups to the 9th position of fluorene, the rotaxane formation was attempted via 1,3 dipolar cycloaddition in the presence of CB(6). A white light emitting diode is prepared using a hybrid inorganic and organic material based system. Prepared conjugated polymers were used in white light generation. Good results are obtained with high CRI indices. Also the thermal stability of the conjugated polymers is studied by FT-IR, UV-VIS and Fluorescence spectroscopic techniques under heat exposure.
Open Access
Multifunctional conjugated polymer nanoparticles as an anticancer drug carrier and a fluorescent probe for cell imaging
(2012) Gezici, Özlem
The main motivation of this study is to develop multifunctional nanoparticles which can perform simultaneously the drug delivery and cell imaging tasks. To this end, firstly nanoparticles (Nps) with an average diameter of about 25 nm and based on a green emitting, hydrophobic conjugated polymer, poly[(9,9-bis{propenyl}fluorenyl-2,7- diyl))-co-(1,4-benzo-{2,1,3}-thiodiazole)] (PPFBT) and Nps with an average diameter of about 150 nm and based on a red emitting, hydrophobic conjugated polymer, poly[(9,9-bis{3-azido-propyl}fluorenyl-2,7-divinylene)-co-(1,4-benzo- {2,1,3}-thiodiazole)] (PAPFVBT) were prepared, characterized and their convenience as a fluorescent probe for cell imaging was evaluated via in vitro cell assays. Then, drug loaded nanocapsules in which PPFBT or PAPFVBT acts both as a fluorescent reporter and the main matrix of the nanocapsules accommodating an anticancer drug, camptothecin (CPT), were synthesized through a facile, single step reprecipitation method. CPT is a hydrophobic, water-insoluble drug but the encapsulation improved its water-solubility. The CPT loading efficiency in the nanoparticles has been determined to be 100% when a drug to polymer ratio of 1:25 (w/w) was used. Cell viability of Human hepatocellular carcinoma cell line (Huh7) was investigated in the absence and presence of CPT using Sulforhodamine B (SRB) assay. SRB assay results supported further by the fluorescence microscope cell images clearly confirmed that blank and CPT-loaded PPFBT Nps have been taken up by the cells very efficiently and these nanoparticles were accumulated in the cytoplasm. Time and dose dependent SRB assay results indicate that the blank PPFBT Nps are not toxic to the Huh7 cells up to 25 µM. However, even a very low dose of CPT was found to be sufficient to induce the apoptosis of the cells when it was delivered through nanoparticles. Thus, at the end of 48 h, the half maximal inhibitory concentration (IC50) of free CPT and CPT-loaded PPFBT Nps were calculated to be 0.9 µM and 0.1 µM respectively, corresponding to that CPT-loaded PPFBT Nps are 9 times more effective than free CPT. However, at the end of 72 h, the IC50 of free CPT and CPT-loaded PPFBT Nps decreased to 0.1 µM and 0.008 µM, respectively. In this case, CPT-loaded PPFBT Nps are 12.5 times more effective than free CPT in inducing the apoptosis of Huh7 cells. Although the free drug (CPT) reaches IC50 of 0.1 µM after 72 h, it is possible to achieve this value with CPT-loaded Nps at the end of 48 h. On the other hand, dose dependent SRB assay results indicate that the blank PAPFVBT Nps are not toxic to the Huh7 cells up to 16 µM. At the end of 72 h, IC50 of free CPT and CPTloaded PAPFVBT Nps were calculated to be 0.03 µM and 0.1 µM respectively, corresponding to that CPT-loaded PAPFVBT Nps are 3.3 times less effective than free CPT. Having bigger size (~150 nm) of PAPFVBT Nps is the main reason of not being effective as PPFBT Nps (~25 nm).
Open Access
Supramolecular chemistry of cucurbit[n]uril homologues with a ditopic guest and light emitting conjugated polymers
(2011) Artar, Müge
The general objective of this thesis is to explore the ability of cucurbit[n]uril (CB[n]) (n= 6,7,8) homologues to form nano-structured supramolecular assemblies with various organic guests through self-sorting, self-assembly and recognition. In the first part of the thesis, the selectivity and recognition properties of CB[n] homologues towards a ditopic guest have been investigated. The guest was synthesized through Cu(I)-catalyzed click reaction between the salts of N,N'-bis-(2- azido-ethyl)-dodecane-1,12-diamine and propargylamine and contain two chemically and geometrically distinct recognition sites, namely, a flexible and hydrophobic dodecyl spacer and a five-membered triazole ring terminated with ammonium ions. Complex formation between the guest and CB[6], CB[7] and CB[8] in the ratios of 1:2, 1:1 and 1:1, respectively, was confirmed by 1H NMR spectroscopy and mass spectrometry. It was also revealed that CB[n] homologues have ability to self-sort and recognise the guests according to their chemical nature, size and shape. Kinetic formation of a hetero[4]pseudorotaxane via sequence-specific self-sorting was confirmed and controlled by the order of the addition. In the second part, the effect of CB[n] homologues on the dissolution and the photophysical properties of non-ionic conjugated polymers in water were investigated. A fluorene-based polymer, namely, poly[9,9-bis{6(N,N dimethylamino)hexyl}fluorene-co-2,5-thienylene (PFT) was synthesized via Suzuki coupling and characterization was performed by spectroscopic techniques including 1D and 2D NMR(Nuclear Magnetic Resonans), UV–vis, fluorescent spectroscopy, and matrix-assisted laser desorption mass spectrometry (MALDI-MS)(Matrix Assisted Laser Desorption/Ionization Mass Spectroscopy ). The interaction of CB[6], CB[7] and CB[8] with PFT have been investigated and it was observed that only CB[8] among other CB homologues forms a water-soluble inclusion complex with PFT. Furthermore, upon complex formation a considerable enhancement in the fluorescent quantum yield of PFT in water was observed. The structure of resulting PFT@CB[8] complex was characterized through 1H-NMR and selective 1DNOESY(The Nuclear Overhauser Enhancement Spectroscopy) and further investigated by imaging techniques (e.g. AFM(Atomic Force Microscopy), SEM(Scanning Electron Microscopy), TEM(Transmission Electron Microscopy) and fluorescent optical microscopy) to reveal the morphology. The results suggested that through CB[8]-assisted self-assembly of PFT polymer chains vesicle-like nanostructures formed. The sizes of nanostructures were also determined using dynamic light scattering (DLS(Dynamic Light Scattering)) measurements.
Open Access
Synthesis and characterization of cross-linked water-dispersible conjugated polymer nanoparticles
(2012) Ekiz, Şeyma
In this study, a novel synthetic method was demonstrated for the water-dispersible crosslinked light-emitting conjugated polymer nanoparticles with enhanced stability. In order to synthesize the novel conjugated polymer nanoparticles, thiophene-based monomers were synthesized with different functional groups such as bromine, hydroxyl and azide groups. These monomers were characterized by 1H-NMR spectroscopy. After the synthesis of the monomers, various polymers were synthesized via Suzuki coupling and oxidative polymerization. Their structural and optical properties were fully characterized by spectroscopic techniques such as 1H-NMR spectroscopy, FT-IR spectroscopy and Gel Permeation Chromatography (GPC). Finally, crosslinked conjugated polymer nanoparticles were synthesized by a diaminoalkyne crosslinker and various useful functional groups were introduced to the nanoparticles such as triazoles and amine groups. Incorporation of the hydrophilic functional groups to the conjugated polymer nanoparticles resulted with patchy, janus-like nanoparticles. CB6 was used as a catalyst for the first time in nanoparticle synthesis for 1,3-azide alkyne Huisgen cycloaddition which formed a conjugated polymer-based nanosized rotaxanes. Crosslinking of the conjugated polymer nanoparticles was also achieved by the irradiation of the nanoparticles under UV light in order to get shape-persistent nanoparticles. Various functional groups of the conjugated polymer nanoparticles make them highly versatile for biological studies such as cell imaging and drug delivery in biological systems. Synthesized nanoparticles were fully characterized by dynamic light scattering (DLS) measurement, transmission electron microscopy (TEM), FT-IR spectroscopy and UV-Vis spectroscopy.
Open Access
Synthesis and characterization of water dispersible conjugated polymer nanoparticles
(2011) İbrahimova, Vusala
In this study, novel water dispersible conjugated polymer nanoparticles having various potential applications in the areas including biomedicine and photonics have been synthesized from blue, green and yellow light emitting conjugated polymers. Their sizes, morphology, surface charges and optical properties have been determined using various techniques. Cell viability of nanoparticles was tested in mesenchymal stem cells. For the synthesis of nanoparticles, first the following polymers carrying a number of different functional groups and based on derivatives of fluorene and benzothiodiazole monomers are designed and synthesized using the Suzuki coupling reactions: Poly[(9,9-bis{propeny}fluorenyl-2,7-diyl)-co-(9,9-dihexyl-9H-fluorene)] (P1), poly[(9,9-bis{carboxymethylsulfonyl-propyl}fluorenyl-2,7-diyl)-co-(9,9-dihexyl-9Hfluorene) (P2), poly[(9,9- bis{propeny}fluorenyl-2,7-diyl))-co-(1,4-benzo-{2,1,3}- thiodiazole)] (P3), poly[(9,9- bis{carboxymethylsulfonyl-propyl}fluorenyl-2,7-diyl)- co(1,4-benzo-{2,1,3}-thiodiazole)] (P4), poly[(9,9-bis{3-bromopropyl}fluorenyl- 2,7-diyl)-co-(1,4-benzo-{2,1,3}-thiodiazole)] (P5), poly[(9,9-bis{3- azidopropyl}fluorenyl-2,7-diyl)-co-(benzothiadiazole)] (P6). Polymers were characterized by using spectroscopic techniques such as 1H-NMR, FT-IR, UV-Vis, Fluorescence spectrophotometer and Gel Permeation Chromatography (GPC). Conjugated polymers carry functional groups on their side chains, such as azide and allyl groups that can be cross-linkable using UV light to form shape-persistent, stable nanoparticles. Nanoparticles were characterized by various techniques before and after UV-treatment. Their sizes and morphologies were determined by using dynamic light scattering measurements (DLS) and imaging techniques such as scanning electron microscopy (SEM) and atomic force microscopy (AFM). For optical characterization UV-vis, fluorescent spectroscopies and FT-IR were used. CNPs affect on cells shows their nontoxic and biocompatible properties which give opportunity to use them in cell imaging.
Open Access
Synthesis of vertically aligned CNT arrays using liquid based precursors and their functionalization by conjugated polymers
(2011) Baykal, Beril
In the first part of this work, a new solution based catalyst precursor application method is developed for growing high quality vertically aligned carbon nanotubes arrays (VANTA) through alcohol catalyzed chemical vapor deposition (AC-CVD). For this purpose, various solution based precursor preparation routes are investigated starting from γ-Al2O3 / Fe(NO3)3.9H2O mixtures and ranging to catalyst precursors prepared by mixing aqueous aluminium and iron nitrate solutions. Application of these solutions separately layer by layer on Si(100) substrate resulted in high quality dense vertically aligned CNT arrays. By varying the metal nitrate concentration in the precursor solutions, the dependence of the density and quality of CNT arrays on the catalyst layers are investigated. The CNT array quality and density are characterized by dynamic contact angle measurements using water droplets. Higher density CNT arrays resulted in higher contact angle measurements. The chemical and structural characterizations of CNTs are also done by using TEM, SEM, EDX and Raman spectroscopy. Some of the samples are found to be super hydrophobic even after 30 minutes of exposure to water. In this effort, application of subsequent layers of aqueous aluminium nitrate and iron nitrate on oxidized Si(100) surfaces are found to be most efficient catalyst layer preparation technique resulting in the highest density of CNT arrays. In the second part of this work, functionalization of the synthesized CNT arrays is done for the purpose of achieving good dispersibility of CNTs in aqueous media. To this end, a new approach is used to ensure stability of the CNT-water solution. In this approach, conjugated polymer nanoparticles (CPNs) are successfully used to disperse CNTs through non-covalent functionalization of the sidewalls of CNTs. The attachment of CPNs to CNTs is characterized by SEM, EDX and TEM. Moreover, interactions are investigated by UV-VIS, and Raman spectroscopy. The interaction mechanism of polymer chains with side-walls of CNTs are further scrutinized by follow-up experiments where two different conjugated polymers with brominated-alkyl and bare alkyl groups in THF media are mixed with SWCNTs (commercial), MWCNTs and an-MWCNTs (synthesized in the first part of this study). The results of this investigation suggested a limited number of docking configurations of the polymers with the CNT side-walls. Also, it is found that the defect density of the CNT side-walls play an important role in the nature of the interaction. Overall, in this work a cheap and effective route for application of catalyst is developed for the synthesis of dense, super-hydrophobic CNT arrays using ACCVD. Then, well-dispersion of these CNTs is successfully achieved using CPNs. Finally, the nature of the interaction between conjugate polymers and CNTs sidewalls are investigated using experimental techniques.
Open Access
Theoretical simulations of UV-Vis and UP spectra for conjugated systems
(2009) Alkan, Fahri
Due to their unique electro-optical properties, there has been a great deal of scientific interest in electronic structure of conjugated systems. In order to reveal the complete map of their electronic structure, several experimental investigations are done using UV-Vis and ultraviolet photoelectron spectroscopy (UPS). The experimental findings are usually interpreted by the results of quantum chemical calculations. In this study, we present the theoretical simulations of UV-Vis and UP spectra of conjugated systems by using density functional theory (DFT). In UV-Vis simulations, we investigated the excited states of oligothiophene anions and cations and almost identical UV spectra were obtained for these systems. This similarity in excitation energies are explained by the resemblance in energy levels and nature of excited states in anions and cations. In UPS simulations, the energy levels of conjugated systems were calculated by using ∆SCF/TDDFT and DFT orbital eigenvalues. It is shown that there is a good agreement between ∆SCF/TDDFT and experiment, especially for the investigated oligomers. In contrast, DFT orbital energies are considerably lower than the experiment. However, spacing of energy levels is consistent with both experiment and ∆SCF/TDDFT.