Stability Studies of Poly(3-hexylthiophene) and Synthesis and characterization of some Metallo-Supramolecular Polymers

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The thesis entitled DStability Studies of Poly(3-hexylthiophene) and Synthesis and Characterization of Some Metallo-Supramolecular PolymersD is divided into two parts. First part discusses stability of poly(3-hexylthiophene), an important conjugated polymer. Second part discusses synthesis and characterization of some metallosupramolecular polymers. Poly(3-hexylthiophene) (P3HT)) is a very important conjugated polymer which finds wide applications in optoelectronics. Despite the vast and many more applications of P3HT, very modest effort has been devoted to understand their detailed thermal decomposition behavior. Mostly available literature only discusses basic thermal studies without any established thermal decomposition route. We could realize that insight into the details changes of P3HT, that take place when they are subjected to high temperatures, especially during device fabrication is important area to be focused. We took up the project and a plausible degradation route is proposed based on the experimental details acquired from gas chromatography, Raman spectroscopy, FTIR spectroscopy, powder X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. Moreover, photo stability of P3HT is not good enough and it degrades in organic solvents containing dissolved molecular oxygen when irradiated with ultraviolet light. We could show that preparation of composites of P3HT with appropriate amounts of multiwalled carbon nanotubes (MWCNT) result in superior photostability of P3HT. UV visible and fluorescence spectroscopy have been used as primary tools to study the photostability of P3HT and its composites. This enhanced photostability of P3HT on preparing composites with MWCNT in addition to its easy processability directly from solution makes these composites immensely important for optoelectronic applications. Photoluminescence quenching of P3HT upon addition of carbon nanotubes was an important phenomenon that we observed. We could establish the nature as Dstatic quenchingD from the results of photoluminescence spectroscopy and time resolved photoluminescence spectroscopy. Metallo-supramolecular polymers potentially offer the functionality of the metal ion along with the processability of the polymer and this makes them advantageous over the conventional polymers. Designing of efficient ditopic monomers with effective metal binding sites has been a wide area of research. Recently, interest has developed in synthesizing terpyridine ligand based metallo-supramolecular polymers as because they form chelate with metal ions which increase the stability of the polymeric systems. Coordination behavior of benzimidazole, 2-substituted benzimidazoles and benzothiazoles, towards transition metal ions are well established. Looking into the important biological activities of the benzothiazole nucleus, and its similarities in binding modes with benzimidazole as well as availability of easy synthetic methods, we pursued the synthesis of benz0thiazole based ditopic monomers and used it for metallo-supramolecular polymer formation. One of our monomer, apart from forming polymers, showed well ability in selectively recognizing resorcinol from among the other toxic benzene metabolites. Another monomer, with a pentaethylene based ethereal spacer showed remarkable propensity to fold in solut.
Supervisor: P K Iyer