Novel intramolecular electron transfer in axial bis(terpyridoxy)phosphorus(V) porphyrin studied by time-resolved EPR spectroscopy

Laser flash-induced spin-polarized transient electron paramagnetic resonance (TREPR) spectra for bis(terpyridoxy)phosphorus(V) porphyrin in a nematic liquid crystal isotropic and in frozen solution are presented. At room temperature, two sequential spin-polarized TREPR spectra are observed. The firs...

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Bibliographic Details
Published in:Applied magnetic resonance 2006-06, Vol.30 (3-4), p.605-618
Main Authors: Kandrashkin, Y. E., Poddutoori, P. K., van der Est, A.
Format: Article
Language:English
Subjects:
Atomic energy levels
Electron paramagnetic resonance
Electron spin
Electron transfer
Electrons
Liquid crystals
Low temperature
Molecular motion
Nematic crystals
Phosphorus
Polarization (spin alignment)
Porphyrins
Room temperature
Spectra
Spectrum analysis
Spin-orbit interactions
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Summary:Laser flash-induced spin-polarized transient electron paramagnetic resonance (TREPR) spectra for bis(terpyridoxy)phosphorus(V) porphyrin in a nematic liquid crystal isotropic and in frozen solution are presented. At room temperature, two sequential spin-polarized TREPR spectra are observed. The first is consistent with the triplet state of a radical pair, while the later is assigned to the triplet state of the porphyrin formed by charge recombination. On the basis of the spectroscopic and redox properties of the terpyridine and porphyrin moieties it is proposed that electron transfer from the terpyridine to the excited phosphorus(V) porphyrin occurs. The lifetime of the radical pair is estimated to be of about 175 ns. At low temperature, the radical pair spectrumis no longer observed and the spin polarization pattern of the porphyrin triplet is dramatically different. This behavior is explained by postulating that the electron transfer is inhibited at low temperature because molecular motion is required to stabilize the radical pair. It is proposed that in the absence of this stabilization, the porphyrin triplet state is populated via spin-orbit coupling-mediated intersystem crossing from the excited singlet state.
ISSN:0937-9347
1613-7507
DOI:10.1007/BF03166221