Date of Award

12-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemistry

Advisor

Echegoyen, Luis

Committee Member

Pennington , William

Committee Member

Stuart , Steven

Committee Member

McNeill , Jason

Abstract

Solar energy can be envisioned as a long term alternative to rapidly depleting fossil fuels. The energy from the sun can be harnessed by constructing donor-acceptor (D-A) type devices where the incident photon induces the transfer of an electron from the donor to the acceptor. If recombination is prevented, this electron can then be channeled through an external circuit, thus leading to the generation of photocurrent. Porphyrins, which are the naturally occurring pigments in photosynthesis, have been widely established as donors while fullerenes, such as C60 and C70 , due to their unique electron accepting properties, have been considered as acceptors. The conversion efficiency of these systems has recently reached about 5%; efficiencies greater than 11% are required for these systems to be economically viable. Thus, in order to further improve their efficiency better electron acceptors which can prevent charge recombination more efficiently than C60 and C70 are required.
This study is aimed at investigating the use of multishell fullerenes, also known as carbon nano onions (CNOs), as possible candidate for electron acceptors in D-A systems. An easy and economical method for the synthesis of these CNOs is established. The synthesized particles are completely characterized and their reactivity is demonstrated using functionalization strategies such as cycloaddition, oxidation, and radical addition reactions. Further, these inherently insoluble particles are rendered soluble in polar as well as non-polar media by functionalization with lypophilic and hydrophilic groups. Their solution properties are studied using NMR, UV-Vis, Raman and fluorescence spectroscopies as well as by electrochemistry. The electrochemistry confirms the ability of CNOs to accept electrons and undergo reduction. Finally, a supramolecular D-A system employing CNOs and tetraphenyl zinc porphyrin is demonstrated
In addition to these studies various porphyrin and fullerene based dyads have been investigated with the intent to determine the optimum geometry for photoinduced charge transfer. These studies offer important clues about the relationship between the structure of the dyad and the charge transfer process.

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