Abstract
A new bent-core mesogen combining a 4-cyanoresorcinol unit with two terephthalate based rod-like wings and terminated by two long alkyl chains, was synthesized and investigated by DSC, XRD, optical, electrooptical and dielectric methods. A series of liquid crystalline phases in the unique sequence SmA-SmA(P)-SmCPR-(M1/SmCPα)-SmCsPA-SmCPA-SmCaPA, mainly distinguished by the degree and mode of correlation of tilt and polar order, was observed. The development of polar order is associated with the emergence of a small tilt (<10°). With decreasing temperature the tilt changes from random (SmA) via synclinic to anticlinic, while the coherence length of the polar domains grows. This small tilt gives rise to an only weak layer coupling which is in competition with the polar coupling and this leads to new modes of self assembly in lamellar phases of bent-core mesogens, among them the SmCPR and the SmCPα phases. The SmCPR phase is an only slightly tilted biaxial smectic phase with randomized polar order and the SmCPα phase is a slightly tilted and antiferroelectric switching, but uniaxial smectic phase. For this phase a regular change of the in-plane polarization vector between the layers by an angle between >0° and <90° is proposed.
Highlights
Liquid crystalline (LC) materials with a bent molecular shape represent a fascinating area in so matter science, providing new supramolecular structures, phenomena and properties, unknown for other materials.[1]
Compound 1/14 forms a wide variety of different smectic phases which allows a unique study of the combined development of tilt correlation and polar correlation depending on temperature
Based on the investigations reported in this paper the possibility of formation of weakly tilted phases must be taken into consideration in the discussion of the LC phases of these compounds, especially for compounds with relatively long alkyl chains
Summary
Liquid crystalline (LC) materials with a bent molecular shape (banana-molecules) represent a fascinating area in so matter science, providing new supramolecular structures, phenomena and properties, unknown for other materials.[1].
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