Separation of the exchange and dipolar contributions to the spin-spin coupling in the donor-acceptor complex TAPD-ZnP-NQ

A. Van Der Est, G. Fuechsle, D. Stehlik, Michael R Wasielewski

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The donor-acceptor complex, 2-tetraalkylphenylenediamine-zinc porphyrin-2-naphthoquinone (TAPD-ZnP-NQ), is studied using transient EPR at K-band (24 GHz). Spin polarized spectra of the radical pair TAPDNQ and of the triplet state TAPD-3ZnP-NQ are observed simultaneously following light excitation of the complex at 30 K in frozen solutions 2-methyl-tetrahydrofuran and the liquid crystal BDH E7. In the liquid crystal, the complex is partially ordered and the spectra depend on the orientation of the sample with respect to the magnetic field. The orientational distribution function is obtained independently by simulating the spectra of the triplet state and assuming that the principal axes of the order matrix coincide with those of the inertia tensor as has been found for solutes in nematic phases. The spectra of TAPDNQ are analyzed on the basis of the coupled correlated radical pair (CCRP) model using an estimate of the geometry based on the X-ray crystal structures of the components and the independently obtained orientational distribution function. It is shown that the experimental spectra are consistent with the assumed geometry and that the exchange coupling, J, is approximately 0.1 mT. This value is at least two orders of magnitude larger than that found in the analogous radical pair PQ in photosynthetic reaction centres. This difference is rationalized in terms of different mechanisms for the exchange coupling.

Original languageEnglish
Pages (from-to)317-335
Number of pages19
JournalApplied Magnetic Resonance
Volume13
Issue number3-4
Publication statusPublished - 1997

Fingerprint

Naphthoquinones
Liquid Crystals
Exchange coupling
spin-spin coupling
porphyrins
Distribution functions
Ion exchange
zinc
Photosynthetic Reaction Center Complex Proteins
Geometry
Tensors
Paramagnetic resonance
Crystal structure
atomic energy levels
Magnetic fields
X rays
distribution functions
liquid crystals
tetrahydrofuran
extremely high frequencies

ASJC Scopus subject areas

  • Spectroscopy
  • Atomic and Molecular Physics, and Optics

Cite this

Separation of the exchange and dipolar contributions to the spin-spin coupling in the donor-acceptor complex TAPD-ZnP-NQ. / Van Der Est, A.; Fuechsle, G.; Stehlik, D.; Wasielewski, Michael R.

In: Applied Magnetic Resonance, Vol. 13, No. 3-4, 1997, p. 317-335.

Research output: Contribution to journalArticle

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