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Optically activated shutter using a photo-tunable short-pitch chiral nematic liquid crystal
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic illustration of the photo-tunable device. For the device to appear dark initially between crossed polarizers and when illuminated with white light, the central wavelength of the reflection band, , must be substantially less than 400 nm.

Image of FIG. 2.
FIG. 2.

Molecular structures of the photo-responsive axially chiral bis(azo) dopants.

Image of FIG. 3.
FIG. 3.

Absorption spectrum of compounds (a) and (b) in Fig. 2 at a mole fraction of 10 mol./l and 10 mol./l, respectively, in the solvent dichloromethane. Absorption of the -isomers (black line) and absorption of predominantly the -isomers (red line).

Image of FIG. 4.
FIG. 4.

Reversible tuning of the reflection band of the photo-responsive chiral nematic LC mixture consisting of 5 wt.% compound (a) in Fig. 2 , 2 wt. % of compound (b) in Fig. 2 , and 7 wt. % of the photo-insensitive chiral dopant R2011. (a) Transmission spectra showing a red-shift of the reflection band when illuminated with UV light for a period of 35 s and a power density of 5mW/cm. (b) The central wavelength, , as a function of time for the red-shift in the reflection band. (c) The transmission spectra showing a blue-shift of the reflection band when illuminated with visible light ( = 625 nm) with a power density of <1 mW/cm. (d) The corresponding central wavelength, , as a function of time for the blue-shift in the reflection band.

Image of FIG. 5.
FIG. 5.

The change in “brightness” of the photo-tunable chiral nematic liquid crystal between crossed polarizers when the pitch is elongated. (a) Photographs of the change in the transmission. Each photograph corresponds to a different pitch, which is obtained by illuminating the sample with UV light with a power density of 5 mW/cm. The duration of the UV exposure time increases from left to right and starts from the pre-exposed state (far-left) extending to an exposure time of 35 s (far-right). (b) Plot of the simulated results of the “brightness” as a function of . (c) Plot of the photo-diode response when the device, which is in the transmissive state, is irradiated with 532 nm laser device and a power density of 229 mW/cm.

Image of FIG. 6.
FIG. 6.

An optically activated shutter. Photographs of the device taken on a backlight before (a) and after (b) illumination with UV light ( = 365 nm) through a photo-mask. (c) Photograph of the LC sample in reflection mode without polarizers.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Optically activated shutter using a photo-tunable short-pitch chiral nematic liquid crystal