CISS effect demonstrated in mesoscopic helical supramolecules

Scientists at the Institute for Molecular Science (IMS) has accomplished an impressive feat in the realm of enantioselectivity. They managed to achieve this without the use of chiral catalysts or chiral ingredients. Instead, they utilized helical supramolecules composed entirely of achiral molecules, tapping into the chiral-induced spin selectivity (CISS) effect.

What’s intriguing is that the helicity of these supramolecules isn’t derived from the typical microscopic molecular arrangements. Instead, it arises from mesoscopically introduced dislocations. This discovery has now expanded the scope of the CISS effect, revealing its relevance not just at the microscopic level, but also at the mesoscopic scale. Their groundbreaking research, published in Nature Communications on July 28, highlights the potential for multifunctional applications spanning various scales – an important aspect in the development of safer chemicals and advanced electronics.

The CISS effect hinges on the spin of electrons, a factor that plays a crucial role in manipulating the chirality of a system. Electrons possess intrinsic angular movement, referred to as spin, which can manifest in two distinct directions. When the spin of two electrons differs, they can coexist in the same space. Conversely, if their spins match, they repel each other – akin to the repulsion experienced when attempting to push together the like poles of two magnets. This fascinating discovery opens up new avenues for controlling chirality and advancing scientific understanding across scales.

Electrons navigating through a chiral system exhibit a preference for a specific spin due to the influence of the CISS effect on chiral interactions. This intriguing phenomenon enables the selective filtering of electrons with a particular spin and molecules possessing a specific preferred chirality.

Co-corresponding author Takuro Sato, an assistant professor at IMS, emphasized the significant role of the CISS effect in conferring enantioselectivity to chiral molecules without requiring chiral catalysis. However, their experiments have thus far been limited to applying CISS-based enantioselection to microscopic targets, focusing on selecting one enantiomer from a mixture. The question that remains is whether this effect can be harnessed to create larger-scale one-sided chiral structures from achiral components.

To explore this potential, Sato and his team directed their attention to the superstructure of cobalt phthalocyanines, a non-chiral organometallic molecule commonly used in electronic devices like LEDs. These molecules can be overlapped onto themselves.

The researchers employed a physical vapor deposition technique to facilitate the reconstitution of molecules into crystallized supramolecules on silicon substrates coated with magnetic nickel. This process yielded helical superstructures with both left- and right-handed chirality, confirmed through scanning electron microscopy.

Magnets were positioned beneath the substrates, orienting a specific pole toward the substrate to control the nickel’s directional magnetism. The interaction between the magnetized nickel and the synthesized helical supramolecules demonstrated intriguing results. Close proximity of the south pole induced left-handedness, while the north pole led to right-handedness. Without magnets, no handedness preference was observed.

Sato highlighted the exploitation of enantiospecific interaction driven by CISS, showcasing enantioselectivity in assembling mesoscale helical supramolecules using non-chiral cobalt phthalocyanines. This reveals the extension of CISS-based enantioselectivity beyond microscopic chirality to the mesoscopic realm.

In contrast to previous experiments that induced chiral flow at a macroscopic scale through classical means, their approach harnessed purely electromagnetic fields in a quantum manner to create the chiral field. This highlights the universal nature of enantioselectivity based on chiral influence, independent of field specifics.

Sato and his team intend to further explore CISS effect applications in larger-scale helical systems, investigating potential implications for advanced optics and sensor technologies.

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