Studies on porphyrin-based nanorods for artificial light harvesting applications

Mongwaketsi, Nametso Precious (2014-04)

Thesis (PhD)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: The work presented in this thesis throws light on the supramolecular approach in exploration of bi-porphyrin nanorods system wherein self-assembly plays an important role. Porphyrin based nanorods were synthesized via self-assembly of meso-tetrakis (4-phenylsulfonicacid) porphyrin dihydrochloride and Sn (IV) tetrakis (4-pyridyl) porphyrin. Understanding the sizes and growth mechanism of the porphyrin nanorods by self-assembly and molecular recognition is essential for their successful implementation in nanodevices. Spectroscopic and microscopic studies were carried out to investigate the effect that time, concentration and solvents have on the fabrication of the porphyrin nanorods by ionic self- assembly. This study demonstrated that aggregates of the di- acid form of meso-tetrakis (4-phenylsulfonic acid) porphyrin dihydrochloride and Sn (IV) tetrakis (4-pyridyl) porphyrin resulted in porphyrin nanorods with diameters between 20 nm and 60 nm, and μm in lengths. Enhanced optical properties illustrated the potential for slightly modifying the method of synthesis to influence the physical and optical properties of porphyrin nanorods. The porphyrin nanorods reflectance data demonstrated that these structures are good absorbers of light and therefore could potentially be used to harvest light. The nonlinear optical (NLO) properties of the porphyrin nanorods were investigated for the first time in this study by second and third harmonic generation techniques. Such study was influenced by the fact that porphyrins have great thermal stability and extended -conjugated macro cyclic ring which give them large nonlinear optical effects. The NLO results showed that the porphyrin nanorods may have many potential uses in photonic applications due to larger third order nonlinear susceptibility. Single molecule spectroscopy was also used to investigate the dynamics of intermolecular and intramolecular processes. Porphyrin nanorods were incorporated into polymer matrices to achieve an arrangement where they can be directly used as a device. The assembly of porphyrin nanorods on track-etched membranes was achieved through altering the surface charge of the respective membranes. Porphyrin nanorods-polymer composites were produced using latex technology and electrospinning techniques. The fibres were characterized with respect to morphology and optical properties.

AFRIKAANSE OPSOMMING: Die werk wat in hierdie tesis beskryf word werp lig op die supramolekulêre benadering in die ondersoek van bi-porfirien nano-silinders waarin self-versameling ‘n belangrike rol speel. Porifirien nano-silinders was voorberei via self-versameling van meso-tetrakis(4-feniel sulfoonsuur) porfirien dihidrochloried en Sn (IV) terakis (4-piridiel) porfirien. Dit is belangrik om die meganismes wat verband hou met die groei en grootte van die nano-silinder struktuur te ondersoek. Dit het ‘n invloed op die self-versameling asook die uiteindelike toepassing. Spectroskopiese en mikroskopiese studies was uitgevoer om die effek van tyd, konsentrasie en oplosmiddel op die selfversamelling te bestudeer. Die studie dui daarop dat bondels van die disuur vorm van meso-tetrakis(4-feniel sulfoonsuur) porfirien dihidrochloried en Sn (IV) terakis (4-piridiel) porfirien het gelei tot porfirien nano-silinders met lengtes tussen 20 nm en 60 nm asook in die mikro meter skaal. Verhoogde optiese eienskappe het die potensiaal om effense veranderinge in die metode om die nano-silinders voor te berei om sodoende ‘n groter invloed op die fisiese en optiese einskappe te hê. Die reflektansie data wys dat hierdie strukture goeie absorbsies van lig toon en daarom geskik sal wees om lig te stoor. Die nie-liniêre optisie (NLO) eienskappe van die profirien nano-silinders was vir die eerste keer ondersoek deur middel van tweed en derde hormoniese generasie tegnieke. Hierdie studie was beïnvloed deur die feit dat porfiriene goeie stabiliteit by hoë temperatuur en ‘n verlengde -gekonjugeerde makro-sikliese ring bevat wat dan groot nie-liniêre optiese effekte gee. Die NLO resultate wys dat die profirien nano-silinders groot potensiaal het in die gebruik van fotoniese toepassings as gevolg van derde orde nie-liniêre vatbaarheid. Enkel molekuul spektroskopie was ook gebruik om die dinamika van intermolekulêre en intramolekulêre prosesse te ondersoek. Porfirien nano-silinders was geïnkorporeer in polimeer matrikse om ‘n eweredige verspreiding te verkry en om direk as ‘n toestel te gebruik. Die versameling van porfirien nano-silinders op baan-ingeëtse membrane was bereik deur die verandering in oppervlak lading van die membrane. Porfirien nano-silinder / polimeer samestellings was verkry deur lateks tegnologie en elektrospin tegnieke. Die vesels was gekarakteriseer in terme van morfologie en optiese eienskappe.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86772
This item appears in the following collections: