# Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience
## 3 Photonic Applications
Recent progress has demonstrated that SPR also exists in monolayers of graphene [270], graphene ribbons [271] and other 2D materials [272; 273]. Compared to the SPR in gold nanoparticles, the SPR in graphene possesses lower propagation loss and stronger mode confinement in the mid-IR spectra [274; 218; 275]. [PERSON] et al. recently discussed the theoretical possibility of manipulating the SPR effect of graphene monolayers and ribbons by modulating the dielectric properties of the neighbouring LC media [276]. According to their modelling, the graphene monolayers/ribbons were coated with a LC layer and, by altering the applied electric field or the surface anchoring, the LC director would be reoriented and thus vary the SPR spectra due to changes in the dielectric characteristics of the LC layer on the graphene monolayers/ribbons and the polarization of the incident light. On the other hand, due to the enhanced light absorption of SPR, gold nanoparticles and graphene can also act as heat nano-sources when excited by a specific wavelength of light, i.e., act as photothermal agents. Over the past decade, the photothermal effect has been a fertile ground for fundamentally new scientific research. Among the various inorganic (e.g., metal and carbon nanomaterials) and organic (e.g., indocyanine green and polyaniline) photothermal agents, gold nanoparticles and graphene have attracted particular attention due to their high photothermal conversion efficiency as well as their NIR-absorbing spectra, which make them extraordinarily popular in biological applications [277; 278; 279; 280]. Remote manipulation of LCs through the photothermal effects induced by particular nanomaterials is an emerging field of promising materials [281; 282; 283; 284; 285]. The functional nanoparticle-LC composites are driven by light when the photothermal nanomaterial absorbs the light energy and converts it into heat, leading to a local increase in temperature. Consequently, the remotely triggered local temperature increase induces morphological and physical changes [23]. Recently, [PERSON] et al. presented an optical manipulation of the plasmonic thermal effect induced by randomly distributed gold nanoparticles coupled with a nematic LCs director field (E7) as an active medium. The authors reoriented the LC director by employing a photoalignment material, which produced changes in both the thermal conductivity and the refractive index of the LCs surrounding the nanoparticles, thus enabling optical  
Figure 9: Electric switching of SPR-enhanced fluorescence intensity of gold-silica–dye nanoparticles (GSDs) in a nematic LC matrix. (**a**) Fluorescence micrograph showing the GSD–LC composite in a planar glass cell. (**b**) Fluorescence spectrum of GSDs in the nematic LC. (**c**) Polarization-dependent fluorescence intensity. (**d**) Voltage-dependent fluorescence of GSDs in a nematic LC. (**e**) Switching of GSDs’ fluorescence intensity by an electric field. (**f**) Voltage-dependent ON and OFF switching times obtained from the change of transmission I-I\({}_{0}\) versus time curves. Reproduced with permission from [267]. Copyright (2016) American Chemical Society. control of their SPR and of the resulting heating [286]. Moreover, a tunable helical pitch and a reversible handedness inversion of cholesteric LCs (CLCs), enabled by the photothermal effect, were demonstrated by [PERSON] et al. The authors dispersed mesogen-functionalized gold nanorods into CLCs. Upon irradiation with NIR light, the photothermal effect of the dispersed gold nanorods commenced, triggering the change of the helical pitch and the handedness inversion of the helical superstructure from left-handedness to right-handedness through an untwisted transient state (see Figure 10). The effect is based on the temperature dependence of the pitch of the helical superstructure of the cholesteric (chiral nematic) liquid crystal. To achieve an inversion of the helical handedness, special materials or mixtures are needed, which exhibit a temperature-induced twist inversion.