Highlighting spin selectivity properties of chiral thin film under an applied magnetic field

The study of the mutual influence between chirality, spin and magnetism is a thoroughly documented field of fundamental research [1], and spin-dependent electrochemistry (SDE) is quite recent, attracting branch of electrochemistry [2]. In particular, the combination of spintronics with magneto-electrochemistry, involving truly chiral molecular spin selectors, was promoted by the discovery of the Chiral Induced Spin Selectivity (CISS) effect by Ron Naaman and coworkers, observing spin polarization in photo-ejected electrons transmitted through a thin layer of enantiopure material adsorbed on gold, acting as an electron spin filter [1]. In this frame we present an innovative set-up, in fact unlike former CISS experiments, in the present case (i) the electrode support is non-ferromagnetic and, most importantly, (ii) a wide potential shift as a function of the applied magnetic field is observed, rather than a current variation [3]. Electron transfer on non-ferromagnetic electrodes coated with chiral conductive thiophene-based films [4] resulted in an impressive shift of the half-wave potential of two achiral Fe(III)/Fe(II) redox couples under an external magnetic field, either upon flipping the magnetic field orientation with a constant layer configuration or inverting the chiral layer configuration with a constant field orientation [3,5,6]. Such spin-related redox potential modulation, obtained in the absence of a magnetic electrode acting as a spin injector, provides striking evidence and an attractive evaluation criterion of the spin selectivity properties of chiral thin films. Such a novel and appealing condensed state system, of easy preparation under ambient conditions, might also be exploited as a “potentiometric” spin-sensitive sensor or a “redox” spin injector, opening the way to innovative spintronic devices.