Determination of the energy levels of radical pair states in photosynthetic models oriented in liquid crystals with time-resolved electron paramagnetic resonance

Haim Levanon, Tamar Galili, Ayelet Regev, Gary P. Wiederrecht, Walter A. Svec, Michael R. Wasielewski

Research output: Contribution to journalArticle

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Abstract

We report the results of time-resolved electron paramagnetic resonance (TREPR) studies of photoinduced charge separation in a series of biomimetic supramolecular compounds dissolved in oriented liquid crystal solvents. The molecules contain a chlorophyll-like (zinc 9-desoxomethylpyropheophorbide a) electron donor, D (ZC), and two electron acceptors with different reduction potentials, i.e., pyromellitimide, A1 (PI), and 1,8:4,5-naphthalenediimide, A2 (NI). The compounds investigated are ZCPI, ZCNI, and ZCPINI, and they have small but well-defined differences of their ion-pair energies. Temperature-dependent TREPR studies on this series of compounds permit the determination of the radical pair energy levels as the solvent reorganization energy increases from the low-temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal. As the temperature is increased, the radical pair with the lowest energy is the first to exhibit triplet-initiated charge separation as the solvent reorganization energy increases in the liquid crystal. The energy levels of the radical pairs and the solvent reorganization energy are determined by using the known singlet and triplet excited state energy levels of ZC, the electrochemically determined relative energies between the radical ion pairs in polar isotropic solvents, and the TREPR data. All these yield information about the ordering of the radical ion pair energy levels relative to the excited-state energy levels of ZC.

Original languageEnglish
Pages (from-to)6366-6373
Number of pages8
JournalJournal of the American Chemical Society
Volume120
Issue number25
DOIs
Publication statusPublished - Jul 1 1998

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Liquid Crystals
Electron Spin Resonance Spectroscopy
Liquid crystals
Electron energy levels
Paramagnetic resonance
Ions
Excited states
Temperature
Electrons
Biomimetics
Chlorophyll
varespladib methyl
Glass
Zinc
Crystalline materials
Molecules

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Determination of the energy levels of radical pair states in photosynthetic models oriented in liquid crystals with time-resolved electron paramagnetic resonance. / Levanon, Haim; Galili, Tamar; Regev, Ayelet; Wiederrecht, Gary P.; Svec, Walter A.; Wasielewski, Michael R.

In: Journal of the American Chemical Society, Vol. 120, No. 25, 01.07.1998, p. 6366-6373.

Research output: Contribution to journalArticle

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