Recent Developments in Fluorescent Liquid Crystal Displays for Advanced Optoelectronic Applications

Fluorescent liquid crystal displays (FLCDs) developed through adding fluorescent dye molecules into the liquid crystal (LC) hosts to enhance optical efficiency and brightness of the displays, have become promising in contrast to the traditional liquid crystal displays (LCDs). The basic principles, materials and new technological advances in FLCD systems are discussed in the present review. The principle of operation of FLCDs under an applied electric field relies on the electro-optical (E-O) switching of LC molecules, which concurrently allows directing scaffold-based fluorescent dyes and regulating fluorescence intensity, polarization and color. Common FLCD architectures are based on nematic LC (NLC) hosts like E7 or 5CB(4-pentyl-4'-cyanobiphenyl), fluorescent dyes like perylene, coumarin, rhodamine and anthracene analogs, transparent indium tin oxide (ITO) electrodes and polyimide (PI) alignment layers. Several technologies like dye doped LC systems, guest host FLCDs, photo responsive and optically switchable displays, polarized fluorescent LC materials and electrically switchable fluorescent devices have shown critical advancements in brightness, contrast ratio (CR), response time and color purity. The color gamut of a conventional LC display (LCD) system has also been extended using advanced fluorescent backlight technologies based on quantum dots (QDs) and perovskite nanomaterials. In spite of these advancements, dye aggregation, photobleaching, fluorescence quenching and long-term stability are some of the challenges that are of great concern. Continued research on novel fluorescent materials, nanostructured dopants and optimized device architectures is expected to enable high efficiency, low power and next generation fluorescent LCD technologies.