Abstract
Cholesteric liquid crystals (CLCs) are self-organized helical nano-structures that selectively reflect certain wavelength of a circularly polarized light. For most CLCs, the handedness is fixed once a chiral dopant is employed. Here, we report a handedness-invertible CLC through opposite-handed doping of a photo-sensitive chiral azobenzene dopant and a photo-stable chiral dopant. With high solubility of the photo-sensitive chiral dopant, the Bragg reflection can be tailored from right-handed to left-handed upon UV exposure. The reversed process can be easily carried out through heating.
Highlights
In a cholesteric liquid crystal (CLC), the orientation of each layer is self-organized in a planar helical structure [1]
We measured the behavior in its post-exposure form where most of the chiral molecules are in cis-form and the reflection band lies in infrared region
After ~8 s of the same UV exposure, the band reappeared and moved towards a shorter wavelength. These reflection bands seemed similar to previous ones, by using a polarized light source we identified that they had an opposite handedness
Summary
In a cholesteric liquid crystal (CLC), the orientation of each layer is self-organized in a planar helical structure [1]. In the past two decades, optical tuning of the helical twisting power has been realized [3,4,5,6,7,8] and wide applications of optically tunable devices such as tunable lasers, gratings and displays have been demonstrated [9,10,11,12,13,14,15,16] This tuning was done through introducing azobenzene or azoxybenzenes functional group into chiral materials. In a relatively recent work, Gvozdovskyy et al [23] demonstrated that through doping of different handedness chiral materials, one can obtain CLC with different handedness This eliminates the need of complicated design of molecular structure. With high chirality and effective twisting power, we are able to tune the reflection band to near-infrared region and tailor the reflection to longer wavelength and eventually invert the chirality, resulting in opposite-handed infrared reflection through UV exposure. We studied and formulated the band-shifting behavior and demonstrated a patterned opposite-handed cholesteric reflection
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