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Chiral molecules and the electron spin

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Abstract

The electron’s spin is essential to the stability of matter, and control over the spin opens up avenues for manipulating the properties of molecules and materials. The Pauli exclusion principle requires that two electrons in a single spatial eigenstate have opposite spins, and this fact dictates basic features of atomic states and chemical bond formation. The energy associated with interacting electron clouds changes with their relative spin orientation, and by manipulating the spin directions, one can guide chemical transformations. However, controlling the relative spin orientation of electrons located on two reactants (atoms, molecules or surfaces) has proved challenging. Recent developments based on the chiral-induced spin selectivity (CISS) effect show that the spin orientation is linked to molecular symmetry and can be controlled in ways not previously imagined. For example, the combination of chiral molecules and electron spin opens up a new approach to (enantio)selective chemistry. This Review describes the theoretical concepts underlying the CISS effect and illustrates its importance by discussing some of its manifestations in chemistry, biology and physics. Specifically, we discuss how the CISS effect allows for efficient long-range electron transfer in chiral molecules and how it affects biorecognition processes. Several applications of the effect are presented, and the importance of controlling relative spin orientations in multi-electron processes, such as electrochemical water splitting, is emphasized. We describe the enantiospecific interaction between ferromagnetic substrates and chiral molecules and how it enables the separation of enantiomers with ferromagnets. Lastly, we discuss the relevance of CISS effects to biological electron transfer, enantioselectivity and CISS-based spintronics applications.
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... Before concluding this introduction, we emphasize that developing tools to study nonadiabatic transitions with spin degrees of freedom is very important for making progress on one of the most exciting themes today in physical chemistry: the chiral induced spin selectivity (CISS) effect. 35,36 Recent experiments have demonstrated that, when a current passes through a chiral molecule, that current is often very spin-polarized, and this spin polarization can increase as temperature increases. 37 Thus, understanding nuclear dynamics in the presence of both spin and electronic degrees of freedom would appear crucial for developing a comprehensive model of the CISS effect. ...
Preprint
Nuclear Berry curvature effects emerge from electronic spin degeneracy and canlead to non-trivial spin-dependent (nonadiabatic) nuclear dynamics. However, such effects are completely neglected in all current mixed quantum-classical methods such as fewest switches surface-hopping. In this work, we present a phase-space surface-hopping (PSSH) approach to simulate singlet-triplet intersystem crossing dynamics. We show that with a simple pseudo-diabatic ansatz, a PSSH algorithm can capture the relevant Berry curvature effects and make predictions in agreement with exact quantum dynamics for a simple singlet-triplet model Hamiltonian. Thus, this approach represents an important step towards simulating photochemical and spin processes concomitantly, as relevant to intersystem crossing and spin-lattice relaxation dynamics.
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Preprint
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... 16,17 Recently, a new approach for simple implementation of spintronic devices have emerged relying on the chiral-induced spin selectivity (CISS) effect. 18,19 CISS effect-based devices benefit from the high spin filtering efficiency thus alleviating the need for a permanent magnetic layer. This significantly simplified the device architecture and resulted in increased operation efficiency. ...
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