Extreme modulation of liquid crystal viscoelasticity altering the ester bond direction

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2021-08, Vol.9 (31), p.999-9996
• Main Authors: Tang, Wentao, Deng, Minghui, Kougo, Junichi, Ding, Li, Zhao, Xiuhu, Arakawa, Yuki, Komatsu, Kenta, Tsuji, Hideto, Aya, Satoshi
• Format: Article
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d1tc01636a

The understanding of correlations between molecular details and macroscopic material behavior is a fundamental question of molecular chemistry/physics and offers practical interest in materials design with fine-property-tunability. Herein, we demonstrate extreme modulation of liquid crystal (LC) viscoelasticity triggered by a reversion of the ester bond direction in two series of sulfur-containing cyanobiphenyl-based LC dimers. They possess two oppositely directed ester linkages ( i.e. , C&z.dbd;OO or OC&z.dbd;O), namely COO n and OCO n , respectively, and different carbon atom numbers of the short alkylene spacers ( n = 4 and 6). Unexpectedly, it has been proven that the COO n homologs exhibit extraordinarily enhanced viscoelastic properties in the fluidic nematic (N) phase (up to about 1000 times) compared with their OCO n counterparts. Besides, dielectric spectroscopy revealed that the degree of the collective orientational fluctuation is significantly affected by reversing the ester bond direction, suggesting the existence of heliconical clusters embedded in the N state. Finally, we have proposed a novel eco-driving LC memory device based on a pulse-electric-field driving method using COO 4 with an extremely high rotational viscosity. Extreme modulation of macroscopic viscoelastic properties (up to about 1000 times) in asymmetric liquid crystal dimers was successfully realized by altering only the ester bond direction in molecular structure.