Photochemical Modulation of Bragg-Reflection Wavelengths in Cholesteric Liquid Crystals Containing a Chiral Azobenzene

  • Lee, Hyoung-Kwan (Department of Polymer Chemistry, National Institute of Materials and Chemical Research) ;
  • Goo, Chul-Whoi (Division of Image and Information Engineering, College of Engineering, Pukyong National University) ;
  • Tomiki Ikeda (Chemical Resources Laboratory, Tokyo Institute of Technology)
  • 발행 : 2000.09.01

초록

가시광을 선택적으로 반사하는 광 응답성 코레스테릭 액정을 조제하고, 그 선택적 반사파장의 광화학적 변조를 시도함으로서 포토닉스(Photonices) 재료로서의 가능성을 검토했다. 고유의 선택 반사파장의 변조는 아조벤젠 유도체의 트란스(trans)·시스(cis)간의 광이성화에 의해 상전이 온도와 칼라의 변화와 함께 가역적으로 제어되어질 수 있었다. 또한 선택 반사파장의 변화에 수반되는 반사율의 변화는 코레스테릭 액정과 검출광의 광학적 성질에 의해 크게 좌우되어 지고, 반사율의 가역적인 스위칭에 있어서는 검출광에 대한 코레스테릭 액정의 초기 반사파장의 위치는 상반된 스위칭 모드(normal and reverse modes)를 산출하기에 매우 중요한 역할을 담당했다.

Photochemical modulation of Bragg-reflection wavelengths based on isomerization of an azobenzene (Azo) and subsequent change in reflectance was investigated in cholesteric liquid crystals (ChLCs) which reflect light in visible wavelength region. Irradiation at 366 nm, which causes an efficient transcis isomerization of Azo, led to change in reflected color of ChLCs toward shorter wavelengths with a concomitant lowering of phase transition. Reversible change in color was induced all-optically by alternate irradiation at effective wavelengths for reversible isomerization of Azo. A considerable variation in reflectance was also observed when the photoinduced change in color was measured by a probe light with the same handedness as the ChLCs. The spectral Position of selective light reflection in the initial states played an important role to produce a normal-mode and a reverse-mode switching in photoinduced modulation of reflectance of the ChLCs with respect to the probe light.

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