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Title: Dendrimeric light-harvesting system
Author: Dyal, Kuljit Kaur
ISNI:       0000 0004 5993 1731
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2015
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Energy is an important term in our daily life. The modern economy is mostly dependent upon non-renewable energy sources such as fossil fuels. However, dependence on fossil fuels generating some severe issues related to energy security and greenhouse gas emissions. This fossil fuel dependence could be avoided by designing light-harvesting systems. Therefore, this thesis describes the synthesis of dendrimeric light-harvesting model systems, which can efficiently transfer light energy from each of its donor molecules on the surface, to a single acceptor unit. In our system, dendron acted as a scaffold to hold the acceptor and the donor unit at a specific distance. The first part of this thesis describes the synthesis of dendrons up to G-4.0 and different chromophores. Preliminary studies towards light-harvesting was carried out using tin(IV) porphyrin as an acceptor and zinc porphyrin as donor units. The ester terminated dendrons were chosen for self-assembly studies, as these dendrons showed stronger interactions than amine terminated dendrons. The successful self-assembly between an acceptor (SnTPP(OH)2), ZnTPP and ester terminated dendrons was achieved. However, the light-harvesting could not be achieved for this acceptor-donor pair because of the similar absorption and emission spectrum of this pair. Then, a different acceptor SnPc(Cl)2 (tin(IV) phthalocyanine dichloride) was chosen. To achieve light-harvesting at a lower concentration range ZnTPP donor unit was not found good enough. Therefore, it was decided to use zinc porphyrin dimer, which was synthesised using mono-nitrated tetraphenylporphyrin. The found binding constant Ka results were 9x103 M-1 (G-1.5), 15x103 M-1 (G-2.5), 16x103 M-1 (G-3.5). These results once again were not good enough to perform the light-harvesting test at lower concentrations range. Therefore, flexible zinc porphyrin dimer (ZnFPD) was synthesised and the found binding constant Ka results at concentration (10-5 -10-6 M) were 1.95x105 M-1 (G-1.5), 1.28x105 M-1 (G-2.5), 1.72x105 M-1 (G-3.5) and were used to perform the LH studies. Finally a self-assembly was achieved using SnPc(Cl)2, ester terminated dendrons and ZnFPD. The confirmation of the self-assembly was achieved using the 1H NMR technique. After observing the successful self-assembly the light-harvesting test was performed for the synthesised dendritic light-harvesting models. The G-0.5 light-harvesting model showed the successful LH behaviour. However, the bigger generation dendron models were failed to show the LH behaviour. This behaviour was assumed due to the inter-quenching within the model systems through PET (photoinduced electron transfer) process via internal tertiary amines. To stop this inter-quenching TFA (10-4 M) solution was used for the protonation of the dendron internal tertiary amines. After the addition of TFA, the bigger generation dendrons showed successful LH behaviour. The calculated quantum yields for the LH complexes of different generation dendrons were 0.07, 0.05, 0.03 and 0.01.
Supervisor: Twyman, Lance Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available