Efficient Transfer of Chirality in Complex Hybrid Materials and Impact on Chirality-induced Spin Selectivity

Abstract

Transfer of chirality, or transmission of asymmetric information from one system to another, plays an essential role in fundamental biological and chemical processes and, therefore, is essential for life. This phenomenon also holds immense potential in spintronics in the context of chirality-induced spin selectivity (CISS). In the CISS, the spatial arrangement of chiral molecules influences the spin state of electrons during the charge-transfer processes. Transfer of chirality from chiral molecules to an achiral material in a hybrid environment enables induction of spin polarization in the achiral material, thus vastly expanding the library of CISS-active electronic materials. Such “induced” CISS signals could have different responses compared to pure chiral molecules because the electronic properties of the achiral material come into play in the former case. In addition, multiple chiral sources can be used, which can have a nontrivial contribution to the induced CISS effect and can act either synergistically or antagonistically. This opens the way to achieving tunability of the CISS signals via chemical means. Earlier, such a chirality-transfer phenomenon and the resulting induced CISS effect were demonstrated in a hybrid system containing carbon nanotubes (CNTs) functionalized with a chiral agent (Fmoc-diphenylalanine l/d). In this context, we extend this result by investigating the role of an additional chiral moiety (l-lysozyme enzyme crystals) in this system. Here, the chiral crystal surrounds the chiral-functionalized CNTs, and we show that synergistic interactions result in more efficient chirality transfer, resulting in nontrivial changes in the CISS effect. This manifests in the form of (a) a stronger CISS signal compared to only one single chiral agent, (b) nonmonotonic temperature dependence and sign reversal of the CISS signal, and (c) persistence of the CISS signal at higher temperatures. Hybrid chiral materials with multiple chiral sources could, therefore, offer intricate control of the CISS signal via modification of its constituents, which is not possible in homogeneous chiral systems with single chiral sources.