Twist–bend nematic phase and heliconical superstructures of thioether-linked liquid crystal dimers

Abstract

The twist–bend nematic (NTB) phase, characterized by a spontaneously formed nanoscale heliconical superstructure from achiral liquid crystal (LC) dimers, represents a fundamental advance in soft matter physics and photonic material design. Sulfur-containing LC dimers, with enhanced molecular flexibility and reduced bond angles, offer promising opportunities for functional NTB materials but remain limited by thermal instability and poorly characterized physical parameters. Herein, we comprehensively investigate a series of thioether-linked symmetric LC dimers (CBSnSCB, n = 3, 5, 7) and their mixtures, revealing how molecular architecture governs phase transition behavior. Judicious blending of multiple homologs significantly suppresses crystallization and extends the supercooled NTB phase stability to room temperature while preserving the phase sequence. Dielectric and elastic analyses demonstrate positive dielectric anisotropy and exceptionally low bend elastic constants, attributed to sulfur-mediated molecular flexibility, which can be further modified by incorporating conventional LCs. Leveraging these unique properties, electrically tunable oblique helicoidal cholesteric superstructures with continuously modulated photonic bandgaps across the entire visible spectrum are constructed. This study establishes a structure–property–function relationship in sulfur-containing LC dimers and offers a versatile platform for engineering stable, functional soft matter systems and adaptive photonic applications.