Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Workers in this and many other labs have been studying photoinduced electron transfer seeking to understand the photochemical processes in photosynthesis. Closely related processes also constitute the basis of some photosensitive tissue diseases and of a wide variety of industrial applications. To study the photophysics unhindered by diffusion, a molecule composed of a freebase porphyrin covalently linked to a p-benzoquinone by an amide linkage was used.;A nanosecond laser flash photolysis apparatus permitted the observation of the porphyrin triplet state decay, with the quinone fully reduced or with it fully oxidized to allow enhanced quenching of the porphyrin triplet via electron transfer. A difference of rate constants in the two cases yielded the electron transfer rate constant which ranged from 1.0 {dollar}\times{dollar} 10{dollar}\sp4{dollar}s{dollar}\sp{lcub}-1{rcub}{dollar} in acetonitrile to 2.8 {dollar}\times{dollar} 10{dollar}\sp5{dollar} s{dollar}\sp{lcub}-1{rcub}{dollar} in methylene chloride. It is shown that the available free energy and the electron transfer rate constants, determined in various solvents over a 40{dollar}\sp\circ{dollar}C temperature range, do not exhibit the relationship put forth by Marcus electron transfer theory.;An alternative hypothesis of a fast equilibrium being established between the triplet porphyrin and a triplet exciplex before the electron reaches a radical-ion-pair state is supported by the observation of negative activation energies in benzonitrile and methylene chloride.;Since neither the radical-ion-pair nor the exciplex were observed as intermediate products, it is not possible to identify conclusively the pathway of deexcitation of the porphyrin triplet state.



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