Abstract
Light technology is based on generating, detecting and controlling the wavelength, polarization and direction of light. Emerging applications range from electronics and telecommunication to health, defence and security. In particular, data transmission and communication technologies are currently asking for increasingly complex and fast devices, and therefore there is a growing interest in materials that can be used to transmit light and also to control the distribution of light in space and time. Here, we design chiral nematic microspheres whose shape enables them to reflect light of different wavelengths and handedness in all directions. Assembled in organized hexagonal superstructures, these microspheres of well-defined sizes communicate optically with high selectivity for the colour and chirality of light. Importantly, when the microspheres are doped with photo-responsive molecular switches, their chiroptical communication can be tuned, both gradually in wavelength and reversibly in polarization. Since the kinetics of the “on” and “off” switching can be adjusted by molecular engineering of the dopants and because the photonic cross-communication is selective with respect to the chirality of the incoming light, these photo-responsive microspheres show potential for chiroptical all-optical distributors and switches, in which wavelength, chirality and direction of the reflected light can be controlled independently and reversibly.
Highlights
Light technology is based on generating, detecting and controlling the wavelength, polarization and direction of light
Microspheres of light-responsive cholesteric liquid crystals were prepared by doping a conventional nematic liquid crystal (E7) with a light-responsive molecular motor 1-(M), at a concentration of 4.9 wt%
The resulting cholesteric liquid crystal is characterised by a pitch p = 3 50 nm and a reflection band centered around λ (0) = 5 30 nm at normal incidence
Summary
Light technology is based on generating, detecting and controlling the wavelength, polarization and direction of light. The emergence of droplet microfluidics have addressed this challenge by providing platforms enabling the large-scale production of micrometer-size objects with well-defined sizes, shapes, and narrow size distributions[4,11,12] In this context, producing microspheres of chiral nematic (cholesteric) liquid crystals shows particular potential as cholesteric liquid crystals reflect light selectively: only a narrow range of wavelengths is reflected, with a specific polarisation. For the part of the droplet where the helical axis is tilted at an angle of θ = 45° with respect to the incoming light beam, the reflected light will be directed towards the plane of the self-assembled microspheres, with equal intensity along all directions This property provides superstructures of chiral nematic microspheres with potential applicability as distributors of light, routing specific wavelengths uniformly towards a certain direction of the sample. Their potential applicability remains limited by their lack of versatility: most all-optical distributors remain beam splitters, with restricted capabilities since they typically split the light into two sub-beams only, or guide the light in a single pre-defined direction[17]
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