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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, λ c, must be substantially less than 400 nm.
Molecular structures of the photo-responsive axially chiral bis(azo) dopants.
Absorption spectrum of compounds (a) and (b) in Fig. 2 at a mole fraction of 10−6 mol./l and 10−7 mol./l, respectively, in the solvent dichloromethane. Absorption of the trans-isomers (black line) and absorption of predominantly the cis-isomers (red line).
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/cm2. (b) The central wavelength, λ c, 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 (λ = 625 nm) with a power density of <1 mW/cm2. (d) The corresponding central wavelength, λ c, as a function of time for the blue-shift in the reflection band.
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/cm2. 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 λ c. (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/cm2.
An optically activated shutter. Photographs of the device taken on a backlight before (a) and after (b) illumination with UV light (λ = 365 nm) through a photo-mask. (c) Photograph of the LC sample in reflection mode without polarizers.
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