Nematic mesophase enhanced via lateral monofluorine substitution on benzoxazole-liquid crystals

ABSTRACT

Fluorine is widely used as a lateral substituent to modify the physical properties of liquid crystals. Here, laterally monofluorinated compounds, 2-(4ʹ-alkoxy-2-fluorobiphenyl-4-yl)-benzoxazole derivatives (nPPF(2)Bx) bearing different substituents (H, CH₃, NO₂, coded as nPPF(2)BH, nPPF(2)BM and nPPF(2)BN, respectively) at 5-position, were synthesised and characterised. It is interesting to note that these only display enantiotropic nematic mesophases with mesophase ranges of 12–28°C and 13–45°C on heating and cooling for nPPF(2)BH, 46–97°C and 62–120°C for nPPF(2)BM and 82–108°C and 87–113°C for nPPF(2)BN, which are very different from the corresponding monofluorine-substituted analogue (compounds I) with enantiotropic smectic or smectic/nematic mesophases. The enhanced nematic mesophase is attributed to the reduced π–π interaction/conjugation resulting from the twisted structure of the molecule caused by the introduction of a fluorine atom into the inter-ring of the biphenyl unit. These results suggest that modification of the monofluorine substituent position is an effective method to improve the nematic mesophase in benzoxazole-liquid crystals.

GRAPHICAL ABSTRACT

KEYWORDS:

• Lateral monofluorine
• nematic mesophase
• benzoxazole-liquid crystals
• inter-ring twist angle

Acknowledgement

The authors thanks for the financial support by the Key Technologies R&D Program of Shaanxi Province (2014K10-06), National Science Foundation Committee of China (51373092, 21543012), Specialized Research Fund for the Doctoral Program of Higher Education (20130202120010), Program for Key Science & Technology Innovation Team of Shaanxi Province (2015KCT-13), Program for Changjiang Scholars and Innovative Research Team in University (IRT_14R33), and the Fundamental Research Funds for the Central Universities (GK201603058, GK201503038, GK201501007, GK201501002). We are grateful to Professor Wenliang Wang at Shaanxi Normal University for theoretical calculations.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed here.

Additional information

Funding

The authors thanks for the financial support by the Key Technologies R&D Program of Shaanxi Province [2014K10-06], National Science Foundation Committee of China [51373092, 21543012], Specialized Research Fund for the Doctoral Program of Higher Education [20130202120010], Program for Key Science & Technology Innovation Team of Shaanxi Province [2015KCT-13], Program for Changjiang Scholars and Innovative Research Team in University [IRT_14R33], and the Fundamental Research Funds for the Central Universities [GK201603058, GK201503038, GK201501007, GK201501002].