Bistable Photochromic Guest–Host Liquid Crystals for Rewritable and Switchable Photonic Devices

Abstract A bistable photochromic guest–host liquid crystal (GHLC) system is presented, enabling reversible optical and electrical modulation for reconfigurable photonic applications. At the core of this system is a newly developed liquid crystalline (LC) dye based on dithienylcyclopentene (DTCP), namely DTCP‐BIPH‐OC8 , which incorporates a biphenyl (BIPH) substituent and an octyloxy (OC8) side chain. This compound combines photoresponsiveness with LC compatibility, displaying excellent miscibility with both nematic and cholesteric liquid crystal hosts. Upon alternating exposure to UV and visible light, this DTCP‐LC dye undergoes a highly reversible transformation between a colorless open‐ring form and a dichroic closed‐ring form with red‐region absorption. The DTCP‐based system demonstrates distinct bistable behavior, characterized by sub‐second switching speed, pronounced optical contrast, and exceptional stability in the closed‐ring state without continuous light input. In cholesteric systems, it enables precise control over three electrically addressable optical states, which are the planar, focal conic, and uniformly lying helix configurations. This photoelectrically tunable absorption, combined with the unique thermal and structural robustness of the DTCP‐LC dye, makes this material a strong candidate for next‐generation rewritable and switchable photonic devices such as tunable optical filters, energy‐saving smart windows, and bistable reflective displays.