Light‐Driven Wide‐Range Nonmechanical Beam Steering and Spectrum Scanning Based on a Self‐Organized Liquid Crystal Grating Enabled by a Chiral Molecular Switch

Abstract

166 wileyonlinelibrary.com COMMUNICATION external stimuli, such as electric fi eld and light. A cholesteric grating with a fi eld-controlled period has been demonstrated. [ 8 ] The diffraction angle can be shifted 15° by varying the applied voltage. A reversible optically switchable beam steering device based on an azobenzene-doped CLC grating has been reported recently, [ 9 ] and it was observed that the grating structure can remain more uniform by the optical tuning than that by electrical tuning. However, the optical tuning range was limit to ≈6° only, because the infl uence of the doped azobenzene upon the pitch was fairly fi nite. It is of paramount importance to develop CLC gratings with reversible wide range beam steering capabilities for optical device applications.In conventional spectrometers, a prism or a diffraction grating spatially separates spectral components of light utilizing wavelength dispersion, which can be detected by an array of photodetectors. [ 13 ] Such spectrometers possess the advantages of easy fabrication and operational simplicity. However, for particular biological and medical analyses, e.g., hyperspectral imaging, [ 14 ] the entire spectrum needs to be recorded at every pixel. Thus, it is diffi cult to be achieved by using spatially dispersive elements. Alternatively, diffraction gratings can be implemented in a frequency sequential scanning system by detecting the incidence angle with mechanically scanning to separate a single spectral component on a single detector. However, the system is bulky and needs high mechanical accuracy. Many methods have been proposed to miniaturize grating dispersive spectrometers. [15][16][17][18] The advantage of a wavelength tunable LC spectrometer is that the entire spectrum can be recreated at single pixel. Nonmechanical tuning can also be realized with an applied external stimulus (light, temperature, electric fi eld) which can further improve the minimized system.In this communication, we report an optically tunable beam steering grating based on a high helical twisting power (HTP) light-driven axially chiral molecular switch-doped CLC fi ngerprint texture. The signifi cant differences of their HTPs resulting from confi gurational changes of the chiral molecular switch upon photoisomerization varies the pitch of CLC, [ 19 ] and consequently shifts the diffraction angle of the CLC grating. Based on this property, the beam steering and spectrum scanning technique have been studied and demonstrated. To the best of our knowledge, this is the LC grating with widest reversible beam steering range reported so far. As a consequence, herein its spectrum scanning capability with potential application in spectrometers as a dispersive element has been demonstrated.In this experiment, the commercially available achiral nematic LC E48 (Merck) with a positive dielectric anisotropy Δ ε Liquid crystals (LCs) are unique functional soft materials with remarkable multistimuli responsive attributes. The LCs formed by rod-shaped molecules have become ubiquitous in ...

The Halogen Bond: An Emerging Supramolecular Tool in the Design of Functional Mesomorphic Materials

“…Recently,t heir potentiali nn umerous beyond display applica-tions have been demonstrated and intense research and development activities in this direction is actively pursued to capitalize on the unique attributes of LC materials. [8][9][10][11][12][13][14][15][16][17] Apart from technological applications, LCs provideg reater and deeper insight into the fundamental understanding of self-assembly and self-organization of matter at different hierarchical levels. [18][19][20][21][22][23][24][25][26][27][28] Extreme sensitivity of LCs to different external stimuli of small magnitude qualifies them as functionals timuli-responsive soft materials.…”

Thermotropic Liquid-Crystalline Materials Based on Supramolecular Coordination Complexes

“…Among metal-based liquid-crystalline materials, those exploiting supramolecular coordination complexes have not yet found a commercial application, however, they are very interesting and they offer great potentials in biology [12][13][14][15][16] and material sciences [17][18][19]. Moreover, and despite having well-established synthetic strategies, the number of papers dealing with supramolecular coordination complexes as liquid-crystalline promoters remains low.…”

Light‐Directed Dynamic Chirality Inversion in Functional Self‐Organized Helical Superstructures

“…As far as the helical superstructure of CLCs are concerned, the use of the terminologies "handedness" and "chirality" to define the helicity of the systems are interchangeable.The CLC superstructure possesses acharacteristic pitch (P)and handedness.T he pitch (P)isthe distance along the helical axis when the molecules complete a3608 8 rotation, in other words the distance when the director describes afull turn, that is,3 608 8.I na ddition to the magnitude, P possesses as ign-either positive or negative-which defines the handedness (i.e.c hirality) of the CLC.Apositive sign represents ar ight-handed CLC,w hereas an egative sign represents al eft-handed CLC.C LCs have found wide application in displays as well as in other devices such as for temperature sensing (thermography), electrooptical displays, all-optical displays without ap atterned electrode,e nergysaving smart windows,l asing, and beam steering as well as apolarizer,reflector,filter, and chiral solvent. [34][35][36][37][38][39][40][41][42] Themost attractive and promising optical property of aC LC is its "selective reflection" of light, which is of interest both fundamentally and technologically.W hen light with aw avelength of the order of the cholesteric pitch strikes aC LC,i t selectively reflects CPL with the same handedness (chirality) as the CLC,but transmits CPL of opposite twist sense,which is referred to as the polarization selection rule. [43] Hence, ar ight-handed CLC reflects right-handed CPL (r-CPL) and al eft-handed CLC reflects left-handed CPL (l-CPL; Figure 2).…”