Electrically Tunable Heliconical Smectic Superstructure in Polar Fluids

ABSTRACT The ferroelectric nematic (N F ) phase and related polar liquid‐crystalline phases form a new class of strongly polarized yet fluid soft matter. Well‐recognized heliconical ferroelectric phases such as N TBF and exist, but their electro‐optic functionality in smectic systems has been largely unexplored. In this study, we report a newly designed single‐component achiral molecule exhibiting a hierarchical polar phase sequence: SmA F– N TBF –HEC–. The key feature of the phase is its ability to form a stable macroscopic orientation without any alignment layers and to enable continuous, reversible pitch modulation over a wide spectral range at ultralow electric fields, approximately one‐third of those required for conventional heliconical nematics. The system exhibits characteristic electro‐optic properties in the sub‐kilohertz range, differentiating it from heliconical materials controlled by dielectric–elastic balance at higher frequencies. In addition, the phase's polar heliconical smectic structure facilitates enhanced second‐harmonic generation via favorable phase matching, thereby establishing a simple and robust platform for low‐voltage photonic applications.