Electrically Tunable Heliconical Smectic Superstructure in Polar Fluids.
basic_science · Level V
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- Record sourced from PubMed, PMID 42427088.
- Also identified by DOI 10.1002/adma.74025.
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Abstract
The ferroelectric nematic (N<sub>F</sub>) 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<sub>TBF</sub> and <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msubsup><mi>SmC</mi> <mi>P</mi> <mi>H</mi></msubsup> <annotation>${\mathrm{SmC}}_{\mathrm{P}}^{\mathrm{H}}$</annotation></semantics> </math> 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<sub>F-</sub>N<sub>TBF</sub>-HEC- <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msubsup><mi>SmC</mi> <mi>P</mi> <mi>H</mi></msubsup> <annotation>${\mathrm{SmC}}_{\mathrm{P}}^{\mathrm{H}}$</annotation></semantics> </math> . The key feature of the <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msubsup><mi>SmC</mi> <mi>P</mi> <mi>H</mi></msubsup> <annotation>${\mathrm{SmC}}_{\mathrm{P}}^{\mathrm{H}}$</annotation></semantics> </math> 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 <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msubsup><mi>SmC</mi> <mi>P</mi> <mi>H</mi></msubsup> <annotation>${\mathrm{SmC}}_{\mathrm{P}}^{\mathrm{H}}$</annotation></semantics> </math> 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.