Optically Rewritable Transparent Liquid Crystal Displays Enabled by Light‐Driven Chiral Fluorescent Molecular Switches

and then impinging on our eyes. Our brain, rightly or wrongly, interprets these and other sensed patterns as reality. Hence, the saying, "seeing is believing."Given that much of our perceived reality is the result of light-matter interactions, it is no surprise that humans have been actively pursuing methods to understand and control the appearance of materials for thousands of years. Through mixing natural dyes of primary colors, people were able to tailor the color of everyday objects by changing their spectral absorption. The science of absorption-based colored materials evolved to the point of creating materials with light-responsive absorption (photochromics) that, when combined with a camera, were used to capture scenes, thereby allowing us to recreate and share moments of reality. Despite huge advances in the ability to control objects' absorptive color over the last 200 years through chemistry, controlling objects' structural color is still quite challenging. Structural color often refers to spectral interference effects associated with periodic spatial changes in the refractive index of materials (sometimes referred to as photonic crystals). These socalled photonic materials are a unique class of materials that have the ability to strongly affect the light-matter interactions for wavelengths on the scale of the refractive index periodicity. Photonic materials have particularly vivid colors that emerge from their angularly sensitive spectral reflections. Some of the early studies in this area were performed on natural photonic materials that caught the eye of curious scientists. [1] There are many examples of naturally occurring self-assembled photonic materials, including opals, [2] Pollia fruit, [3] jeweled beetles, [1,4] chameleons, [5] and others. [6] These natural examples of structurally derived color can be emulated, altered, or reproduced by researchers. [7][8][9] The ability of biology to self-assemble materials with complex structures and functionality is still unrivaled by engineered systems, but unique opportunities now exist for major advances in autonomously adaptive materials, as scientists are deciphering the molecular mechanisms that biology uses to self-assemble amazingly complex adaptive systems. [10] Particularly relevant to this review, some of the photonic structures found in nature are able to change periodicity in Photoresponsive liquid crystalline photonic materials are a medium in which the self-regulation of light can occur. Liquid crystals are macroscopically selfassembling, optically anisotropic materials capable of amplifying photochemical changes and thus are well suited to demonstrate complex light-driven behavior. This review presents recent progress in liquid crystalline systems exhibiting photoresponsive structural color. More specifically, it surveys progress on liquid crystalline materials and structures with coloration that is the result of the constituents' spatial arrangement (not of presence of dyes or pigments) and for which this arrangement can be externally cont...

Section: Naturally Self‐assembled Liquid Crystalline Materialsmentioning

confidence: 99%

Photoresponsive Structural Color in Liquid Crystalline Materials

McConney

Rumi

Godman

et al. 2019

“…Thanks to the aforementioned unique helical structures, CLCs have been widely studied so far and numerous fancy applications based on CLCs have been exploited, such as sensors, displays, lasing, smart windows, beam steering, flexoelectro‐optic devices as well as various optical elements . Whereas all these practical applications need excellent control of the hierarchical architectures in CLCs.…”

Section: Light‐activated Liquid Crystalline Hierarchical Architecturesmentioning

confidence: 99%

Light‐Activated Liquid Crystalline Hierarchical Architecture Toward Photonics

Zheng

et al. 2019

Self Cite

remarkable structure results in a helical-variant dielectric tensor, thus contributing to a natural 1D photonic crystal. [7] It is endowed with a broadband Bragg reflection with a unique circular-polarization selectivity. Blue phase (BP) is another fantastic phase with 3D stacked lattice ( Figure 1D). [8] Such an elegant state-of-matter is energetically preferred in a high chirality system, commonly existing in a narrow temperature range of less than 1 K, between the cholesteric and isotropic phases. It has an exotic arrangement characteristic of LCs, which twists around two helical axes forming cylinders including hierarchically twisted molecular architectures. Such double twisted cylinders are impossible to tile the whole 3D space, which leads to inevitable disclinations and results in frustrated structures.Self-organization is an intrinsic ability of LC molecules. However, the precise control and generation of large-area desirable hierarchical superstructures require state-of-the-art techniques that usually combine the "top-down" microfabrication with the "bottom-up" self-assembly. Here, we review various hierarchical architectures in SLCs, CLCs, and BPLCs, especially recent progresses in light-activated LC hierarchical superstructures, as well as their optics and photonics applications in optics and photonics. In this review, we will see the controllable spatial smectic layer curving via 2D anchoring confinement, 3D topographic confinement, and external field guidance, with which the domain size, shape, orientation, and lattice symmetry of focal conic domain (FCD) arrays are well manipulated. The control of helix direction or fluctuation of CLC layers and the growth of unique fingerprint textures including spiral and wave-like continuous gratings are presented. The 3D manipulation of BPLC hierarchical architecture is accomplished photoalignment and various light-driven azobenzene molecular motors. The construction of these unique hierarchical superstructures brings new opportunities to the design of novel optic and photonic devices. Corresponding applications, including traditional microlens array, beam steering, and more advanced specific optical field generation and LC lasers are comprehensively reviewed as well.

“…Such elegant systems may represent ideal candidates for use as “photonic inks” to realize changeable information in color reflective displays, especially those providing paper‐like viewability in sunlight where backlit devices perform poorly . To this end, phototunable reflection across the visible spectrum has been demonstrated for CLCs and was induced by photoresponsive chiral motors and switches with tetrahedral, axial, or planar chiralities . These triggers undergo photoisomerization, giving rise to both the variations in helical twisting power (HTP) and the color change .…”

Section: Introductionmentioning

confidence: 99%

Photostationary RGB Selective Reflection from Self‐Organized Helical Superstructures for Continuous Photopatterning

Qin

Jia

2019

in response to light, which has unique advantages for remote, temporal, local, and spatial manipulation. [7][8][9][10][11][12][13][14][15][16] Such elegant systems may represent ideal candidates for use as "photonic inks" to realize changeable information in color reflective displays, especially those providing paperlike viewability in sunlight where backlit devices perform poorly. [17][18][19] To this end, phototunable reflection across the visible spectrum has been demonstrated for CLCs and was induced by photoresponsive chiral motors [19,20] and switches with tetrahedral, [21,22] axial, [23][24][25][26][27][28][29][30][31][32] or planar chiralities. [33,34] These triggers undergo photoisomerization, giving rise to both the variations in helical twisting power (HTP) and the color change. [35][36][37][38][39] Detailed colored patterns, including the three primary colors, red, green, and blue (RGB), have been achieved based on light-driven CLCs as well as photomask techniques. However, the existing CLC systems are restricted to displaying static optically addressed RGB images and need to be initialized by light or heat before every subsequent image, which indicates that precise photocontrol of the RGB colors still remains a great challenge. According to the mechanism of color change (HTP variation), the RGB colors only appear in the transition states during the reflection tuning process and are not "fixed" in the photostationary states (PSSs). Thus, an alternative method to directly modulate the RGB colors of the CLCs with light is urgently needed.Herein, we report a new and straightforward strategy to demonstrate continuous patterning of photostationary RGB colors based on a novel partial photochemical phase transition mechanism in the CLCs rather than through HTP variation. It has been reported that the degree of order in photonic structures can be tuned to effectively affect the properties of photonic crystals. [6] In addition, LC alignment can easily be controlled between ordered and disordered states via a photochemical phase transition in the presence of azobenzenes. [40] Combining these two phenomena, we separated a commonly used photo responsive chiral switch into two independent simple structures, i.e., a chiral dopant and a photoswitch (Figure 1a). The chiral dopant is able to immediately induce helical superstructures in the CLCs, and the photoswitch can undergo conformational change upon isomerization, leading to a change in the degree of LC order and, consequently, tuning the pitch of the helices as well as the reflection color (Figure 1b).Light-driven cholesteric liquid crystals (CLCs) are intriguing materials due to the dynamic tuning of their selective reflection, which originates from selforganized helical superstructures, in response to light. However, CLC systems are restricted to displaying static optically addressed images and need to be initialized or refreshed before every new image can be displayed. Herein, a novel tuning mechanism based on a partial photochemical phase transition is propo...