Synthesis of oligomers, polymers and cucurbituril- based polyrotaxanes towards polymer light emitting diode and photodynamic therapy application
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In the first part of this study, porphyrin-thiophene monomers, oligomers and polymer are synthesized for photodynamic therapy application. Water solubility and the ability of a photosensitizer to generate singlet oxygen for tumor destruction are important conditions for ideal photosensitizer in photodynamic therapy application. For this purpose, water soluble pendent groups are attached to the porphyrin monomers before coupling with thiophene monomer to form oligomers and polymer. The presence of sulfur atom in thiophene facilitates intersystem crossing due to spin-orbit coupling and thus will increase singlet oxygen generation. Consequently, the ability of singlet oxygen generation of the polymer is found to be higher than oligomers followed by monomers. In the second part of the thesis, the effects of cucurbit[n]uril on photophysical, electrochemical and thermal properties of ionic conjugated polymers in water are described. Conjugated polymers are well known for their interesting optical properties and are used in the area of light emitting diodes. However, their stacking nature reduces their fluorescent quantum yields and thus limits their further applications. If the interactions among the polymers chains are reduced or the polymer backbones are insulated in some means, the emission efficiency of the polymers could be enhanced. For this purpose, two different green emitting fluorene-thiophene based polymers (29 and 33) and their cucurbituril based polyrotaxanes counterparts (30 and 34) are synthesized through Suzuki Coupling. In both polyrotaxane 30 and 34, enhancement in optical properties was observed showing fluorescent quantum yields of 0.46 and 0.55 in water respectively comparing to polymers 29 and 33 which has only 0.10 and 0.35 in water respectively. Their optical and electroluminescent properties were further utilized by fabricating devices as multilayer white polymer light emitting diodes (PLEDs). The synthesized molecules are characterized by 1H-NMR, 13C-NMR, ESI mass spectrometry, UV-VIS, photoluminescence, time resolved fluorescence spectroscopy, FT-IR, elemental analysis gel permeation chromatography, size exclusion chromatography, thermogravimetric analysis and cyclic voltammetry.
Polymer light emitting diode