An ultrafine pinwheel structure (chiral structure) fabricated using symmetric molecules, analogous to origami folding. [Provided by KAIST]
An ultrafine pinwheel structure (chiral structure) fabricated using symmetric molecules, analogous to origami folding. [Provided by KAIST]

Researchers have developed a technology that controls the rotational direction of light through molecular arrangement alone, without synthesizing new complex chiral materials.

KAIST announced Friday that a research team led by Yoon Dong-ki, a professor in the university's Department of Chemistry, succeeded in arranging non-chiral liquid crystal molecules using an electric field to create micrometer-scale chiral "pinwheel" structures and permanently replicating them in polymer nanofibers. The work was carried out in collaboration with researchers from Chungnam National University, Ajou University, Yonsei University and Japan's RIKEN institute.

Chirality refers to a structural property — like the relationship between a left and right hand — in which a molecule and its mirror image cannot be superimposed. Circularly polarized light, which travels while rotating either leftward or rightward, is considered a key optical technology with applications in next-generation displays, optical communications, optical sensors and security systems.

Conventional approaches to producing chiral optical materials required either synthesizing asymmetric molecules or adding large quantities of chiral substances. That made material development and fabrication complex and difficult to achieve uniform rotational direction across wide areas.

The research team focused on generating chirality through the collective arrangement of molecules rather than through the molecules themselves. The underlying principle is that even non-chiral molecules — which have no inherent left-right distinction — can exhibit chirality at the structural level when arranged collectively in a specific orientation.

The joint research team behind the study. From left: Han Jeong-yeon, a student in KAIST's Department of Chemistry; Heo Jeong-mu, professor at Ajou University; Lee Gyeong-jin, professor at Chungnam National University; and Yoon Dong-ki, professor at KAIST. [Provided by KAIST]
The joint research team behind the study. From left: Han Jeong-yeon, a student in KAIST's Department of Chemistry; Heo Jeong-mu, professor at Ajou University; Lee Gyeong-jin, professor at Chungnam National University; and Yoon Dong-ki, professor at KAIST. [Provided by KAIST]

The team arranged rod-shaped liquid crystal molecules into an ultrafine pinwheel formation, then used a minute quantity of chiral additive — less than 1 percent of the total material — to guide the pinwheel's rotation in a single direction. The resulting structure was then replicated directly onto polymer nanofibers to produce a stable chiral configuration.

When a common luminescent material was introduced into the structure, circularly polarized light emission signals of opposite signs appeared depending on the rotational direction of the structure. This showed that the polarization direction of emitted light can be controlled through the surrounding molecular arrangement, without chemically altering the luminescent material itself into a chiral form.

The team said the technology is expected to serve as a new platform for developing next-generation optical devices, as it allows existing luminescent materials to be combined with structural design rather than requiring the synthesis of complex new chiral emitters.

"The key is that we controlled the rotational direction of light through molecular arrangement alone, not through the chemical structure of complex chiral molecules," Yoon said. "We have proposed a new optical material design principle that can be applied to next-generation displays, AR and VR optical devices, polarization sensors and optical communications."

The findings were published in the journal Nature Communications.


nbgkoo@heraldcorp.com