Using spin dynamics of covalently linked radical ion pairs to probe the impact of structural and energetic changes on charge recombination

Shulamit Shaakov, Tamar Galili, Eli Stavitski, Haim Levanon, Aaron Lukas, Michael R Wasielewski

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Abstract

We have synthesized a series of structurally related, covalently linked electron donor - acceptor triads having highly restricted conformations to study the effects of radical ion pair (RP) structure, energetics, and solvation on charge recombination. The chromophoric electron acceptor in these triads is a 4-aminonaphthalene-1,8-dicarboximide (6ANI), in which the 4-amine nitrogen atom is part of a piperazine ring. The second nitrogen atom of the piperazine ring is part of a para-substituted aniline donor, where the para substituents are X = H, OMe, and NMe2. The imide group of 6ANI is linked to a naphthalene-1,8: 4,5-bis(dicarboximide) (NI) electron acceptor across a phenyl spacer in a meta relationship. The triads undergo two-step photoinduced electron transfer to yield their respective XAn.+-6ANI-Ph-NI.- RP states, which undergo radical pair intersystem crossing followed by charge recombination to yield 3*NI. Time-resolved electron paramagnetic resonance experiments on the spin-polarized RPs and triplet states carried out in toluene and in E-7, a mixture of nematic liquid crystals (LCs), show that for all three triads, the XAn.+-6ANI-Ph-NI.- RPs are correlated radical pairs and directly yield values of the spin - spin exchange interaction, J, and the dipolar interaction, D. The values of J are all about -1 mT and show that the LC environment most likely enforces the chair conformation at the piperazine ring, for which the RP distance is larger than that for the corresponding boat conformation. The values of D yield effective RP distances that agree well with those calculated earlier from the spin distributions of the radical ions. Within the LC, changing the temperature shows that the CR mechanism can be changed significantly as the energy levels of the RPs change relative to that of the recombination triplet.

Original languageEnglish
Pages (from-to)6563-6572
Number of pages10
JournalJournal of the American Chemical Society
Volume125
Issue number21
DOIs
Publication statusPublished - May 28 2003

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Spin dynamics
Genetic Recombination
Liquid Crystals
Ions
1-Naphthylamine
Electrons
Conformations
Liquid crystals
Nitrogen
Imides
Atoms
Ships
Nematic liquid crystals
Exchange interactions
Solvation
Electron Spin Resonance Spectroscopy
Toluene
Boats
Aniline
Naphthalene

ASJC Scopus subject areas

  • Chemistry(all)

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Using spin dynamics of covalently linked radical ion pairs to probe the impact of structural and energetic changes on charge recombination. / Shaakov, Shulamit; Galili, Tamar; Stavitski, Eli; Levanon, Haim; Lukas, Aaron; Wasielewski, Michael R.

In: Journal of the American Chemical Society, Vol. 125, No. 21, 28.05.2003, p. 6563-6572.

Research output: Contribution to journalArticle

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