Effect of terminal chain length on mesomorphic behavior and selective reflection of blue phase liquid crystals

ABSTRACT

A series of new chiral liquid crystal compounds named Mt4BOPnAB containing (-)-menthyl group has been prepared and characterised by FT-IR and ¹H NMR spectra. The series contains nine membersthat vary in the terminal length of the alkanoyloxy chain (C_n−1H_2n−1COO-, where n = 2, 4, 6, 8, 10, 12, 14, 16, 18). The thermal properties and optical properties were investigated by differential scanning calorimetry (DSC), polarising optical microscopy (POM), X-ray diffraction (XRD) and ultraviolet/visible sepctroscopy (UV/Vis). High chiral menthyl group in Mt4BOPnAB molecules triggers the formation of a cubic structure of a blue phase (BPI/II). Increasing the length of the terminal alkanoyloxy group leads to the reduction in T_c, narrowing the N* phase, and contributing to the development of the Sc* phase. In addition, only CLCs with short terminal chains (n ≤ 8) show selective reflection of visible light and themochromic behaviors.

Graphical abstract

KEYWORDS:

• Chiral
• liquid crystal
• (-)-menthol
• chain length
• blue phase
• thermochromic

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Natural Science Foundation of Liaoning Province [2020-KF-12-03] and National Natural Science Foundation of China [11902070]