Development of organic nano-materials that distinguish left and right circularly polarized light

Light can possess the properties of right-handed circularly polarized or left-handed circularly polarized light, which rotate in opposite directions. Materials that can distinguish between these two types of light and transform them into distinct optical signals are considered vital components of future optical technologies. However, implementing clear nonlinear optical signal differences based on right- or left-handed circular polarization in conventional organic materials is challenging, leading to the development of mainly inorganic or organic-inorganic composite materials.

Professor Kim Jin-sang of Kyung Hee University's Department of Advanced Materials Engineering, together with his research team, successfully implemented strong right-handed circularly polarized selective nonlinear optical reactions using only organic materials through international collaborative research with Japan's RIKEN research institute.

Their findings were published in the prestigious journal 'Advanced Functional Materials' in September. Organic materials typically produce weak optical responses due to the weak nature of their magneto-electric related optical reactions. To resolve this issue, the research team utilized the property of liquid crystals to spontaneously form regular structures and created a nanofibrillar three-dimensional chiral molecular structure as the scaffold.

They then filled the structure with a ferroelectric liquid crystal whose molecules spontaneously align in the same direction, resulting in the creation of a chiral organic composite material where structural chirality and ferroelectric polarization are combined in the nanoscale. Upon investigation with a right-handed circularly polarized laser with a wavelength of 800nm, the team observed that the intensity of the second harmonic signal generated at a wavelength of 400nm varied significantly depending on the rotation direction of the light.

Regions with opposite angular orientations of the nanoscale structure exhibited reversed signal strengths. However, when the ferroelectric liquid crystal alone was used without the nanoscale structure, no significant signal differences were observed. The research team concluded that the combination of chirality and ferroelectric polarization in the nanoscale enabled the activation of magnetoelectric-related optical reactions, which increased the signal difference based on right- or left-handed circular polarization by overcoming interference from conventional electric dipoles.

The study's first author, Dr. Je Jae Park, explained that this research presents a novel material design method for implementing strong right-handed circularly polarized selective nonlinear optical reactions using only organic materials. He further noted that the findings are expected to be applied to future optical and optical information technologies such as right- and left-handed circular polarization detection, chiral imaging, and polarization-selective wavelength conversion.

This research was supported by the Korean Research Foundation's Mid-career Researcher Project, the Korea Science and Engineering Foundation's Fellowship Program, and the Korea Industrial Technology and Promotion Institute's Display Technology Development Project.