Dynamic Nuclear Polarization with Conductive Polymers

Abstract

The low sensitivity of liquid-state nuclear magnetic resonance (NMR) can be overcome by hyperpolarizing nuclear spins by dissolution dynamic nuclear polarization (dDNP). It consists of transferring the near-unity polarization of unpaired electron spins of stable radicals to the nuclear spins of interest at liquid helium temperatures, below 2 K, before melting the sample in view of hyperpolarized liquid-state magnetic resonance experiments. Reaching such a temperature is challenging and requires complex instrumentation, which impedes the deployment of dDNP. Here, we propose organic conductive polymers such as polyaniline (PANI) as a new class of polarizing matrices and report ¹H polarizations of up to 5 %. We also show that ¹³C spins of a host solution impregnated in porous conductive polymers can be hyperpolarized by relayed DNP. Such conductive polymers can be synthesized as chiral and display current induced spin selectivity leading to electron spin hyperpolarization close to unity without the need for low temperatures nor high magnetic fields. Our results show the feasibility of solid-state DNP in conductive polymers that are known to exhibit chirality-induced spin selectivity.

Keywords: conductive polymers; dynamic nuclear polarization; nuclear magnetic resonance; spin hyperpolarization.