Science & Technology (Commonwealth Union) – South Korean Scientists have made a key finding that could possibly unlock the spin code of light.
A new approach has emerged for controlling the direction in which light rotates by simply manipulating the collective alignment of molecules, eliminating the need to design and manufacture complicated new materials. Circularly polarized light is a unique form of light that twists and propagates either clockwise or counterclockwise, similar to the motion of a pinwheel. Since each rotational direction can encode different information, it is gaining importance for future technologies such as advanced displays, optical communication systems, and security applications. Researchers have developed a fundamental technique to organize achiral molecules into extremely fine “pinwheel-like” structures, enabling the generation of circularly polarized light with a selected rotational direction.
This month, the university made public that a research team led by Professor Dong-Ki Yoon from the Department of Chemistry, together with scientists from Chungnam National University (President Kim Jeong-Kyum), Ajou University (President Choi Ki-Joo), Yonsei University (President Yoon Dong-Sop), and Japan’s RIKEN Institute, successfully created micrometer-scale chiral pinwheel patterns. The team achieved this by applying an electric field to symmetrical achiral liquid crystal molecules confined within a limited space, and then permanently transferred these structures into polymer nanofibers.
Chirality refers to the characteristic of objects that exist as non-superimposable mirror images of each other, similar to the relationship between the left and right hands. This property plays a crucial role in biological molecules, as well as in advanced optical materials being developed for next-generation displays, optical sensors, and communication technologies.
The fabrication of chiral optical materials has been usually achieved either by chemical synthesis of molecules with complicated asymmetric structures or addition of large quantities of chiral additives up to now. These methods have introduced a number of challenges, including complicated manufacturing processes, limited flexibility in material choice and difficulties in achieving uniform, single-direction optical rotation over large areas.
Scientists attacked this problem by introducing a new concept, that of chirality coming from collective organization.
Their approach generalises the observation that a single sheet of paper can be folded into a clockwise or anticlockwise pinwheel depending on the direction of folding. Applying this principle at the molecular scale, they demonstrated that while individual molecules may not have an inherent left- or right-handed nature, a group of molecules arranged in a specific collective pattern can develop opposite chiral characteristics.
To achieve this, the team designed rod-shaped molecules that spontaneously assembled into nanoscale pinwheel-like structures. By adding an extremely small quantity of a chiral additive—less than 1% of the total composition—they guided all the molecular pinwheels to align in a uniform rotational direction. They then successfully transferred this organized structure onto polymer nanofibers with high precision.
After incorporating a conventional luminescent material into the resulting structure, the researchers observed circularly polarized light signals with opposite rotational properties depending on the direction of the assembled structure. The findings demonstrate that the polarization behavior of emitted light can be adjusted simply by controlling the surrounding molecular arrangement, eliminating the need to chemically modify the luminescent molecules themselves to introduce chirality.
Professor Yoon Dong-ki explained, “The key to this research is controlling the direction of light rotation solely through the ‘arrangement method’ rather than the chemical structure of complex chiral molecules,’ adding, ‘We have presented a new design principle for optical materials that can be utilized in next-generation displays, AR/VR optical devices, polarization sensors, and optical communication without the need to create complex new materials.”
First author Han Jeong-yeon, a doctoral researcher, indicated that in earlier approaches, structures with both left- and right-handed chirality appeared together, which canceled out the overall chiral effect. In this study, however, they introduced a very small amount of an additive that acts as a directional selector.
