Superstructures of chiral nematic microspheres as all-optical switchable distributors of light

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.

Cholesteric solid spherical microparticles: chiral optomechanics and microphotonics

“…The resulting chiral solid micro-particles preserve both spherical shape and internal supramolecular arrangement of the precursor CLC droplets. An alternative strategy to stabilize the liquid crystalline ordering in microbeads relies on the addition of a small percentage of a cross-linking monomer to the LC [21]. However the resulting polymer-stabilized CLC beads exhibits a significant degradation of the cholesteric ordering which affects the optical properties of the particles.…”

“…Chirality in liquid crystals is emerging as a tool to address innovative concepts in materials science, colloidal systems, optical and photonics devices, optomechanics, sensors, and others [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Recent results involving materials science and colloidal systems demonstrate the relevant role of chirality in guiding elastic interactions and promoting particles selfassembling [6][7][8][9][10][11].…”

Elucidating the fine details of cholesteric liquid crystal shell reflection patterns

“…Since the location of the CLC selective reflection band, λ c , can be varied continuously by changing the amount of chiral material in the CLC, the colours of the reflection pattern can be tuned at will. By using photosensitive materials, such tuning can even be accomplished dynamically, after droplet production by exposing them to UV light, as demonstrated by the Li [26] and Katsonis [27] groups. Recently we demonstrated that the most distinct pattern is achieved by using CLC shells rather than droplets, since the reflections are then localised mainly to the surface [28].…”

“…By combining CLCs with right-and left-handed helices in one and the same sample, it is even possible to hide only a fraction of the reflection pattern in this way [27]. In an elegant study, the Kim group combined a temperature-responsive CLC droplet with a surrounding shell of polymer-stabilised CLC, the two CLCs having opposite handedness [31].…”

Transmission polarized optical microscopy of short-pitch cholesteric liquid crystal shells

“…2, 3 Fan et al 4 and Aβhoff et al 5 showed that additional dynamics can be added by incorporating a photoresponsive chiral dopant, and by incorporating cholesteric droplets inside an optically isotropic rubber shell, Lee et al provided high mechanical stability. 6 Following an earlier experiment on lasing from cholesteric droplets, 7 two groups also studied omnidirectional lasing from short-pitch cholesteric shells.…”