City Research Online

Abstract

In order to elucidate the mechanism of important reactions (photo-synthesis, biomimetic methods for harnessing solar energy) it is imperative to understand the principles concerning electron transfer reactions. It is known that compounds in which the redox partners are connected by a flexible chain exhibit intramolecular exciplex formation, intramolecular energy transfer and intramolecular electron transfer. With the intramolecular electron transfer process, the formation of radical ions by electron transfer can and does occur, but the back reaction to produce non-excited species competes. This means that the absorbed electronic energy is completely wasted. This non-productive back electron transfer is due to the radical ions being geminately produced and are not able to diffuse away because of the linking chain. In addition, on linking the two redox groups, it is very difficult to determine the conformational requirements for electron transfer and associated processes such as exciplex fluorescence.

To try to reduce these problems, in this work, the two redox groups were linked via a rigid molecular framework — the b cyclo [2,2,2j - octane framework. A series of 1,4-disubstituted bi cyclo [2,2,2] - octane compounds were synthesised and photochemically investigated. These compounds had an aromatic ring (and some also had an amino and substituted amino group on the aromatic nucleus) and a halogen group separated by the rigid insulating bicyclo [2,2,2] octane frame-work. Photochemical investigation revealed that for those halo- substituted bicyclo [2,2,2] octane compounds that do dehalogenate, the rate of dehalogenation is enhanced if an amine is present during photolysis.

The rigid bicyclo [2,2,2] octane group slows down the back thermal electron transfer. Using a rigid molecular group to separate the redox partners is probably the only way to effectively study conformational effects upon electron transfer reactions.

It would also be interesting to increase the distance between the two redox groups and produce a fairly stable intramolecular radical ion pair.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > Q Science (General) Q Science > QD Chemistry
Departments:	School of Science & Technology School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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