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1. Microsecond electro-optic switching in nematic phase of ferroelectric nematic liquid crystal

   https://doi.org/10.1117/12.3025542  

   Thapa, Kamal; Sathyanarayana, Paladugu; Lavrentovich, Oleg D (September 2024, SPIE)

   Khoo, Iam Choon (Ed.)

   Nematic liquid crystals exhibit nanosecond electro-optic response to an applied electric field which modifies the degree of orientational order without realigning the molecular orientation. However, this nanosecond electrically-modified order parameter (NEMOP) effect requires high driving fields, on the order of 108 V/m for a modest birefringence change of 0.01. In this work, we demonstrate that a nematic phase of the recently discovered ferroelectric nematic materials exhibits a robust and fast electro-optic response. Namely, a relatively weak field of 2×107 V/m changes the birefringence by ≈ 0.04 with field-on and -off times around 1 μs. This microsecond electrically modified order parameter (MEMOP) effect shows a greatly improved figure of merit when compared to other electro-optical switching modes in liquid crystals, including the conventional Frederiks effect, and has a potential for applications in fast electro-optical devices such as phase modulators, optical shutters, displays, and beam steerers. 

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2. Microsecond electro-optic switching in the nematic phase of a ferroelectric nematic liquid crystal

   https://doi.org/10.1364/OE.541317  

   Thapa, Kamal; Paladugu, Sathyanarayana; Lavrentovich, Oleg D (October 2024, Optics Express)

   Nematic liquid crystals exhibit nanosecond electro-optic response to an applied electric field which modifies the degree of orientational order without realigning the molecular orientation. However, this nanosecond electrically-modified order parameter (NEMOP) effect requires high driving fields, on the order of 10^8 V⁄m for a modest birefringence change of 0.01. In this work, we demonstrate that a nematic phase of the recently discovered ferroelectric nematic materials exhibits a robust and fast electro-optic response. Namely, a relatively weak field of 2×10^7 V⁄m changes the birefringence by ≈ 0.04 with field-on and-off times around 1 μs. This microsecond electrically modified order parameter (MEMOP) effect shows a greatly improved figure of merit when compared to other electro-optical switching modes in liquid crystals, including the conventional Frederiks effect, and has a potential for applications in fast electro-optical devices such as phase modulators, optical shutters, displays, and beam steerers. 

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3. First-principles experimental demonstration of ferroelectricity in a thermotropic nematic liquid crystal: Polar domains and striking electro-optics

   https://doi.org/10.1073/pnas.2002290117  

   Chen, Xi; Korblova, Eva; Dong, Dengpan; Wei, Xiaoyu; Shao, Renfan; Radzihovsky, Leo; Glaser, Matthew A.; Maclennan, Joseph E.; Bedrov, Dmitry; Walba, David M.; et al (June 2020, Proceedings of the National Academy of Sciences)

   We report the experimental determination of the structure and response to applied electric field of the lower-temperature nematic phase of the previously reported calamitic compound 4-[(4-nitrophenoxy)carbonyl]phenyl2,4-dimethoxybenzoate (RM734). We exploit its electro-optics to visualize the appearance, in the absence of applied field, of a permanent electric polarization density, manifested as a spontaneously broken symmetry in distinct domains of opposite polar orientation. Polarization reversal is mediated by field-induced domain wall movement, making this phase ferroelectric, a 3D uniaxial nematic having a spontaneous, reorientable polarization locally parallel to the director. This polarization density saturates at a low temperature value of ∼6 µC/cm 2 , the largest ever measured for a fluid or glassy material. This polarization is comparable to that of solid state ferroelectrics and is close to the average value obtained by assuming perfect, polar alignment of molecular dipoles in the nematic. We find a host of spectacular optical and hydrodynamic effects driven by ultralow applied field (E ∼ 1 V/cm), produced by the coupling of the large polarization to nematic birefringence and flow. Electrostatic self-interaction of the polarization charge renders the transition from the nematic phase mean field-like and weakly first order and controls the director field structure of the ferroelectric phase. Atomistic molecular dynamics simulation reveals short-range polar molecular interactions that favor ferroelectric ordering, including a tendency for head-to-tail association into polar, chain-like assemblies having polar lateral correlations. These results indicate a significant potential for transformative, new nematic physics, chemistry, and applications based on the enhanced understanding, development, and exploitation of molecular electrostatic interaction. 

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4. Color Tuning in Ferroelectric Nematic Liquid Crystals using Triptycene/Hydrazone Chiral Photoswitches

   https://doi.org/10.1002/adma.202509125  

   Wang, Hao; Bala, Indu; Wiscons, Ren A; Aprahamian, Ivan (November 2025, Advanced Materials)

   Abstract The development of light‐tunable ferroelectric nematic liquid crystals (N_FLCs) will allow for the multi‐stimuli control over the properties of this newly discovered LC phase. Here on the development of photoresponsive chiral ferroelectric nematic liquid crystals (N_F^*LCs) is reported by incorporating chiral triptycene/hydrazone‐based bistable photoswitchable dopants into the polar liquid crystal mesogen DIO. The propeller‐like dopants exhibit high helical twisting powers with values of 13.5 µm⁻¹in DIO, with a further increase in value to 31.0 µm⁻¹upon 442 nm light‐inducedZ→Ephotoisomerization. This process results in the tuning of the N_F^*LC's reflection color from near infrared, to red, green, and finally blue at 50 °C. The reverse color transition can be induced by 340 nm light irradiation, which drives theE→Zphotoisomerization of the hydrazone. The ferroelectric nature of the N_F^*LC phase is confirmed by applying an alternating current electric field (0.67 V/ µm, 10 Hz, square wave), which initiated azimuthal deformations of the ferroelectric helix. 

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5. Electrically Tunable Polymer Stabilized Chiral Ferroelectric Nematic Liquid Crystal Microlenses

   https://doi.org/10.1002/adom.202302500  

   Perera, Kelum; Haputhantrige, Nilanthi; Himel, Md_Sakhawat Hossain; Mostafa, Md; Adaka, Alex; Mann, Elizabeth K; Lavrentovich, Oleg D; Jákli, Antal (March 2024, Advanced Optical Materials)

   Abstract Tunable optical lenses are in great demand in modern technologies ranging from augmented and virtual reality to sensing and detection. In this work, electrically tunable microlenses based on a polymer‐stabilized chiral ferroelectric nematic liquid crystal are described. The power of the lens can be quickly (within 5 ms) varied by ≈500 diopters by ramping an in‐plane electric field from 0 to 2.5 V µm⁻¹. Importantly, within this relatively low‐amplitude field range, the lens is optically isotropic; thus, its focal length is independent of the polarization of incoming light. This remarkable performance combines the advantages of electrically tuned isotropic lenses and the field‐controlled shape of the lens, which are unique properties of chiral ferroelectric nematic liquid crystals and have no counterpart in other liquid crystals. The achieved lens performance represents a significant step forward as compared to liquid lenses controlled by electrowetting and opens new possibilities in various applications such as biomimetic optics, security printing, and solar energy concentration. 

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