Synthesis and performance evaluation of fluorinated biphenyl diluters for high birefringence liquid crystals

ABSTRACT

Liquid crystal (LC) mixtures with high birefringence (∆n) and low rotational viscosity play an essential role for fast-response LC devices. However, high birefringence and low rotational viscosity are a pair of contradictory performance parameters. In this work, two high-∆n LC diluters are proposed to achieve a fine balance between them. These two terminal olefin diluters containing a rigid biphenyl core with a lateral fluorine substituent, a buty-3-enyl terminal group and a flexible n-alkyl chain were designed and synthesised through classical organic synthetic reactions. Meanwhile, their comprehensive properties were further evaluated in a LC mixture P02-F containing fluoro-tolane and a LC mixture P12-ISO containing isothiocyano-tolane. The results show that the biphenyl diluters 2BBF2V and 3BFB2V could effectively decrease the T_m of LC mixture P12-ISO to below −25°C, while maintain high ∆n and large Δε, which are suitable for the high-∆n LC mixtures containing isothiocyano-tolane. Furthermore, DFT calculations of molecular conformation and polarisability components were utilised to correlate the experimental findings.

GRAPHICAL ABSTRACT

KEYWORDS:

• High birefringence
• liquid crystal
• diluters
• low viscosity
• low melting point

Acknowledgments

The authors thank for the financial support by the National Natural Science Foundation of China (62105194, 52273186 and 51873100); the China Postdoctoral Science Foundation (2022T150394); Sanqin scholars innovation teams in Shaanxi Province, China; International Science and Technology Cooperation Project of Shaanxi Province, China (2021 KW-20), and the Fundamental Research Funds for the Central Universities (GK202103054).

Disclosure statement

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

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [62105194, 52273186 and 51873100] ; the China Postdoctoral Science Foundation [2022T150394]; Sanqin scholars innovation teams in Shaanxi Province, China; the International Science and Technology Cooperation Project of Shaanxi Province, China [2021 KW-20]; the Fundamental Research Funds for the Central Universities [GK202103054].