In Search of Stable, High-Spin Polymers
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Applied Magnetic Resonance
ORIGINAL PAPER
In Search of Stable, High‑Spin Polymers Patrick Hewitt1 · David A. Shultz1 Received: 19 July 2020 / Revised: 18 October 2020 / Accepted: 21 October 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Oligomers of poly(thiophene) and poly(ortho-phenyleneethynylene) having pendant S = 1/2 semiquinone radicals (as complexes of cobalt(III)) have been prepared and characterized by electron paramagnetic resonance (EPR) spectroscopy and magnetic measurements (superconducting quantum interferences device = SQUID magnetometry). Our results show that exchange coupling of semiquinone groups along a polythiophene backbone is greater than the corresponding coupling along a poly(orthophenyleneethynylene) backbone.
1 Introduction Polyradicals were once thought to be possible inexpensive, lightweight, flexible replacements for inorganic magnetic materials [1–3]. While polyradicals can and have found application in a variety of devices and materials, they are probably not going to replace inorganic materials due in part to high molecular weights and low spin densities, and lack of rational three-dimenional coupling schemes [2, 4–6]. However, polyradicals may be able to find application in spintronics [7–10], organic memory storage devices [11–14], photovoltaics [15–17] and organic batteries [18–25]. The preparation and study of radical-containing polymers spans over three decades [2, 21, 26–29]. Much effort has been focused on coupling the paramagnetic centers along a polymer backbone comprising s p2- and/or sp-hybridized carbons and heteroatoms. Carbenes [1, 26, 30], triarylmethyl radicals [31–35], amminium radical cations [18, 36–38], nitroxides/nitronylnitroxides [27, 39], galvinoxyl [27, 39–45], phenoxyl [44], and other radicals have been explored as components of such polymers. Lack of stability, spin localization, intermolecular interactions [6, 17, 37, 39,
Electronic Supplementary Material The online version of this article (https://doi.org/10.1007/s0072 3-020-01293-z) contains supplementary material, which is available to authorized users. * David A. Shultz [email protected] 1
Department of Chemistry, North Carolina State University, Raleigh, NC 27695‑8204, USA
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40, 43, 46, 47], defects, and other drawbacks have hampered the realization of optimal materials [31, 35, 37, 38, 48–51]. Herein, we describe the reaction of a previously prepared poly(ortho-phenyleneethynylene-ortho-benzoquinone) (PoPE-BQ, Fig. 1) and its reaction with a cobalt(II) complex (CoIILA) that results in a polymer with pendant cobalt(II) semiquinone groups (PoPE-SQ). We also present the synthesis of oligomers of poly(thiophene) with pendant quinone groups (PTh-BQ, Fig. 1) that also react with the same cobalt(II) complex to produce another semiquinone-containing polymer (PTh-SQ, Fig. 1). Our preliminary investigation is relevant in the search for new high-spin polymers containing redox-active semiquinones which are known to ch
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