Light‐Driven Reversible Alignment Switching of Liquid Crystals Enabled by Azo Thiol Grafted Gold Nanoparticles

Abstract

Stimuli-directed alignment control of liquid crystals (LCs) with desired molecular orientation is currently in the limelight for the development of smart functional materials and devices. Here, photoresponsive azo thiol (AzoSH) was grafted onto gold nanoparticles (GNPs). The resulting hybrid GNPs were able to homogeneously mix with a commercially available nematic LC host, as evidenced by Cryo-TEM. Interestingly, the LC nanocomposites were found to undergo reversible alignment transition upon light irradiation as a consequence of the trans-cis photoisomerization of the azo groups on the GNP surface. LC molecules in either planar or bare glass cells were able to change their alignment to vertical upon UV irradiation, while the vertically aligned LC molecules returned to the planar or random orientation under visible irradiation. Neither the azo thiol molecules nor the unfunctionalized GNPs alone promoted the alignment of the LC molecules in the system upon light irradiation. The photoinduced vertical alignment without applied electric or magnetic field was very stable over time and with respect to temperature. Furthermore, an optically switchable device based on the photostimulated reversible alignment control of LCs was demonstrated.

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“…However, the underlying mechanisms responsible for such extraordinarily large non-linearity are still not clear. For example, such self-activated switching effects have been also observed in other azobenzene LCs, where the laser-induced photothermal effects and trans-cis isomerism are responsible for orientation disorder of director axis and birefringence modification [60][61][62][63][64].…”

Nature‐Inspired Emerging Chiral Liquid Crystal Nanostructures: From Molecular Self‐Assembly to DNA Mesophase and Nanocolloids

“…[329] Due to the nonradiative relaxation of longitudinal surface plasmon resonances (LSPR), the M-GNRs could convert the external NIR light irradiations into localized heat, i.e., photothermal effect. [330][331][332][333] Thanks to the excellent thermoresponsive properties of BPs, their 3D nanostructures could be manipulated with the "photothermal effect" of M-GNRs. It was found that introducing M-GNRs into BPs enabled not only the stabilization of the cubic nanostructure, but also the reversible transformations of 3D nanostructures between BCC and SC symmetry as well as dynamic RGB reflections upon NIR irradiation at 808 nm.…”

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“…Very recently, Xue et al, reported photoresponsive azo thiol grafted gold nanoparticles for stimuli-directed alignment control of LCs [50]. In this paper, we report a new series of thiolated azobenzene molecules embedded to gold NPs which exhibit nematic and SmA phases irrespective of chain length and parity.…”