New Materials for 3D-Displays

Crystal structure of X-shaped double helicenes. They showed high chiroptical properties due to their high symmetry. (Source: Osaka Univ.)

Chiral molecules are non-super­imposable and play a crucial role in advanced materials and techno­logies. However, there had been no reliable theo­retical systems for the design and synthesis of chiral materials. These systems had seen only gradual development, with chemists making progress on the design and synthesis of chiral materials based on their intuition.

A research group led by Tadashi Mori at Osaka Univer­sity aligned two hexa­helicenes in various orienta­tions, theo­retically examined, and proposed that S- and X-shaped double hexa­helicenes aligned in right symmetry were a key to improve the properties of helicenes. The researchers then synthesized double hexa­helicenes to demonstrate their improved chirop­tical properties as chiral materials: circular dichroism (CD) and circularly polarized lumines­cence (CPL).

They aligned multiple chiral hexa­helicene units to thoroughly examine how their chirop­tical proper­ties would be enhanced by quantum chemical calcu­lations. The results suggested that chirop­tical perfor­mances were enhanced in S- and X-shaped helicenes aligned in right symmetry. The researchers also examined the number of molecules to be aligned and the space between molecules and found the possi­bility that double helicenes, in which two helicenes are merged, could become ideal chiral materials.

Based on the dis­cussion stated above, employing X- and S-shaped pristine double hexa­helicenes as repre­sentative molecular models, this group syn­thesized both double hexa­helicenes, demon­strating drastic improve­ment of their chirop­tical properties. They pursued what factors control chiroptical responses and found that both inten­sity and orien­tation of the electric and magnetic transition dipole moments of the molecules were important.

This group demon­strated the new logical protocol for desig­ning chiral materials: how to rationally align and design molecules. By using strategies beyond conven­tional ways of material develop­ment that were based on intuition, the group dras­tically improved material develop­ment costs. Polarized light can be used for next-gene­ration optical infor­mation tech­nology, so this study will acce­lerate technical inno­vation in the develop­ment of advanced materials for 3D displays and endo­scopes in medical applications, as well as security paint in infor­mation and communi­cation fields. (Source: Osaka Univ.)

Reference: H. Tanaka et al.: Symmetry-based rational design for boosting chiroptical responses, Commun, Chem. 1, 35 (2018); DOI: 10.1038/s42004-018-0035-x

Link: Dept. of Applied Chemistry, Graduate School of Engineering, Osaka University, Osaka, Japan

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