Abstract:
There is considerable interest in intramolecular energy transfer, especially in complexes
which absorb visible light, because it is crucial to the better understanding of photoharvesting
systems in photosynthetic organisms and for utilizing solar energy as well. Porphyrin dimers
represent one of the best systems for the exploration of light-induced intramolecular energy
transfer. Many kinds of porphyrins and porphyrin dimers have been studied over the past decade,
however little attention has been paid to the influence of paramagnetic metals on the behavior of
their excited states. In this thesis, Electron Paramagnetic Resonance Spectroscopy (EPR) is used
to study such compounds. After light irradiation, porphyrins easily produce a variety of excited
states, which are spin polarized and can be detected by the time-resolved (TR) EPR technique.
The spin polarized results for vanadyl porphyrins, their electrostatically-coupled dimers, a
covalently-linked copper porphyrin-free base porphyrin dimer, and free base porphyrins are
presented in this thesis. From these results we can conclude that the spin polarization patterns of
vanadyl porphyrins come primarily from the trip-quartet state generated by intersystem crossing
(lSC) from the excited sing-doublet state through the trip-doublet state. The spin polarization
pattern of electrostatically-coupled vanadyl porphyrin-free base porphyrin dimer is produced by
the triplet state of the free base porphyrin half which is coupled to the unpaired electron on the
vanadyl ion.
