Stepwise Progression of Dye-Induced In Situ Photoalignment and Subsequent Stabilization for Noncontact Alignment of Liquid Crystals.

Noncontact alignment of liquid crystals (LCs) is crucial for large-area and ultrahigh definition (UHD) display manufacturing. This research presents an innovative approach to the photoalignment of LCs, aiming to overcome challenges associated with uniformity and assembly in large-sized and UHD displays. Using homogeneously dissolved, nonionic azobenzene chromophores sensitive to both visible and UV light, we demonstrate an in situ stepwise progression of dye-induced LC alignment and subsequent stabilization using reactive mesogen (RM). Both dual-wavelength and single-wavelength approaches enable stepwise interfacial modifications for LC alignment and stabilization. The dye-induced LC alignment is rewritable, allowing for the creation of various patterns and gray-level alignments. The stability of the alignment is ensured through cross-linked RM layers, providing a robust and permanent solution for LC alignment without the need for delicate mechanical treatments. Importantly, this method addresses the challenges associated with conventional photoalignments, including various dye-induced approaches and high-energy photoalignment. The proposed method exhibits high-quality electro-optical switching, azimuthal anchoring strength, and stability against thermal, radiation, and ac-field stresses, making it a promising candidate for commercial mass production, especially in the fabrication of large-sized and UHD LC displays.

Refractive Index-Adaptive Nanoporous Chiral Photonic Crystal Film for Chemical Detection Visualized via Selective Reflection.

Photonic crystals (PC) are of great importance in technology, especially in optics and photonics. In general, the structural color of PCs responds to external stimuli primarily by changing their periodicity. Herein, the authors report on refractive index (RI) adaptive PCs. Cross-linked cholesteric films with interconnected nanopores exhibit a very low RI without light scattering. Transparent PC films with maximum reflectance in the ultravoilet (UV) region respond to various chemicals by changing the reflective color of the PC. The authors demonstrate its unique colorimetric chemical detections of hazardous organic liquids. Loading various chemicals into nanopores significantly shifts the structural color into the visible range depending on the chemical's RI. These results are unique in that the structural color of photonic films is mediated by RI changes rather than periodicity changes. In principle, nanoporous photonic crystal films can detect the RI of a chemical substance by its unique color. In contrast to volumetric changes, this sensing mechanism offers several advantages, including durability, excellent sensitivity, fast response time, and wide detection range. These results provide useful insight into stimulus-responsive PCs. The structural color of PC films can be effectively tuned by adjusting average RIs instead of changing periodicity.