Chiro‐Spintronics: Spin‐Dependent Electrochemistry and Water Splitting Using Chiral Molecular Films

Abstract

Molecular spintronics or spin‐based electronics, which utilizes both the spin degrees of freedom and electron charge, has become a hot topic in modern science. Since the introduction of spintronics in 1988, many efforts have been devoted to controlling spin‐polarized current using an external magnetic field, leading to the implementation of commercial solid‐state devices based on the giant magnetoresistance effect. In molecular spintronics, much progress has been achieved with organic molecules, but the role played by chiral molecules is yet to be explored in detail, while it promises to play a role in the future. It has been proved that the interaction of electrons with chiral molecules is spin specific, as supported by several experimental tools, and by theoretical studies. This effect is named “chiral‐induced spin selectivity” (CISS). CISS is based on the fact that chiral molecules exhibit spin‐specific transport properties, and hence can be used as a substitute for ferromagnetic materials. Here, recent spin‐dependent electrochemistry results are highlighted, where chiral molecules are immobilized on a ferromagnetic electrode. Practical applications of the CISS effect, for spin control of charge transport in complex molecular architectures, and in the water‐splitting process are also reviewed.

Use of magnetic fields in electrochemistry: A selected review

“…Order of magnitude from 10 3 to 10 transmitted through a chiral molecule, yielding a current of polarized-spins. This "chiral-induced spin-selectivity" (CISS) [44] was applied in several domains [28,[45][46][47]; spinpolarization was observed using FM or antiferromagnetic (AFM) WE [45], and used to reach giant-magnetoresistance [48]. By polarizing the spin through a chiral compound or by applying a magnetic field on a ferromagnetic WE, enhanced electron-transmission was observed for O2 evolution, while the side reaction of H2O2 production was reduced during water-splitting Reproduced from [46] with permission from Wiley.…”

“…[46][49][50][51]. The effect is explained by the more favourable energetic path of the transferred electrons upon polarization: when the OH• radicals reacting into O2 have their electronic spin co-aligned in the laboratory frame, they interact on a triplet potential, yielding triplet oxygen, whereas peroxide formation is symmetry-forbidden (Pauli principle,Figure 2)[46]. One can imagine that by polarizing the electrons, the overlap-integral of the radicals' molecular orbitals is higher than without polarization, leading to the formation of more kinetically-favourable species, even though the thermodynamics is not favoured.…”

Chiral AuCuAu Heterogeneous Nanorods with Tailored Optical Activity

“…The significance of chirality phenomenon has been addressed in different fields, including the evolution of life, [ 1,2 ] enantioselectivity in asymmetrical reactions or biointeractions, [ 3 ] and spin polarization selectivity in chiral nanomaterials for spin chemistry and devices. [ 4,5 ] Nanoparticle fabrication technology have been well developed in recent years that provide rich strategy for chiral construction. [ 6–11 ] Biomolecules, such as amino acids, including cysteine and derivatives, typically display very weak circular dichroism (CD) signals; consequently, only at high concentrations would these biomolecules produce a detectable signal in the ultraviolet (UV) spectral region.…”

“…Phototherapy, including photothermal therapy (PTT) and Photodynamic therapy (PDT), using functional nanomaterials, provide an elegant solution to eradicate tumors for cancer treatment. [ 7 ] The optical active heterostructures provide chirality can benefit for electron spin that further involved in interband transition of noble metal, [ 36–39 ] and thus accelerate the electronic transfer or oscillations [ 5,40,41 ] that can help induce photothermal or photodynamical effect. By the chiral plasmonic nature of optical active metal nanostructures, polarization‐sensitive photochemistry phenomenon that related to hot electrons mediated phototherapy effect was interesting and showed great potential for bioapplications.…”

The Influence of Electronic Structure Modelling and Junction Structure on First-Principles Chiral Induced Spin Selectivity

“…2 This effect has been demonstrated for a variety of molecular systems at room temperature. In addition to its importance for fundamental science, the CISS effect has large potential for applications such as spin-dependent chemistry, electrochemical water splitting, [3][4][5][6] enantiomer separation with achiral magnetic substrates, 7 and spintronic devices. 2,8 It may also contribute to the large efficiency of electron transfer in biological systems due to the coupling of spin angular momentum and linear momentum reducing backscattering.…”