A comprehensive review on molecular design and applications of fluorescent liquid crystals

Fluorescent liquid crystals (FLCs) represent a unique class of functional soft materials that integrate mesomorphic ordering with tunable photoluminescence, enabling diverse applications in optoelectronics, sensing, security technologies, and biomedical imaging. This review presents a comprehensive overview of molecular design strategies, structure–property relationships, and emerging applications of FLCs. Conventional calamitic and discotic systems based on biphenyl, tolane, benzothiadiazole, triphenylene, and phenazine cores are discussed alongside recently developed architectures incorporating aggregation-induced emission (AIE) chromophores, dye-functionalized mesogens, macrocyclic systems, and doped liquid crystal matrices. Calamitic FLCs achieve high quantum yields exceeding 93% with emission tunability across the visible region (494–644 nm), while discotic systems exhibit columnar mesophases with fluorescence efficiencies up to 66% and enhanced charge transport properties. AIE-active cores such as tetraphenylethylene (TPE) and diphenylacrylonitrile effectively overcome aggregation-caused quenching (ACQ) through restricted intramolecular rotation, enabling strong emission in aggregated states. BODIPY-based mesogens provide narrow emission bands and high quantum yields (>80%), whereas porphyrin-based liquid crystals offer red to near-infrared emission advantageous for bioimaging and photonic technologies. Host–guest doping strategies using fluorescent dyes, nanoparticles, and chiral polymers further enhance photophysical performance, enabling circularly polarized luminescence with dissymmetry factors approaching theoretical limits (|g_lum| ≈ 1.87). These smart materials demonstrate broad technological potential in display technologies, anti-counterfeiting systems, bioimaging probes, wearable sensors, and energy-efficient smart windows. Finally, key challenges including aggregation control, thermal stability, and scalable manufacturing are discussed, along with future research directions involving hybrid molecular architectures, thermally activated delayed fluorescence materials, and machine-learning-guided molecular design for next-generation adaptive optoelectronic materials.