Synthesis and examination of alkoxycyanobiphenyl mesogens with a single fluorine atom at specific locations in the tail

ABSTRACT

Selective fluorination is a well-established technique to tailor and improve many of the physical properties of liquid crystals. Cyanobiphenyls are among the best-known and understood thermotropic liquid crystals and have served admirably as a testbed for structural modifications that can eventually be extended to other classes of liquid crystals. As such, and expanding on our earlier work, in the present study of the alkoxycyanobiphenyl M series, the individual tail sites of both 4’-(butoxy)[1,1’-biphenyl]-4-carbonitrile (M12) and 4’-(pentyloxy)[1,1’-biphenyl]-4-carbonitrile (M15) were selectively monofluorinated in order to examine the influence on the phase behavior. These fluorinated compounds were synthesized using epoxidation, regioselective epoxide opening and deoxyfluorination chemistry. In all the fluorinated compounds in both series a monotropic nematic phase was found in the cooling cycle. It was observed that as the fluorine atom on the tail moves closer to the core, the compounds exhibited a metastable room temperature nematic mesophase, but recrystallization invariably occurred. Both enantiomers of 4’-(2-fluorobutoxy)[1,1’-biphenyl]-4-carbonitrile were synthesized in high enantiomeric purity by regioselective opening of chiral epoxide intermediates followed by deoxyfluorination, as established by chiral high-performance liquid chromatography, and their phase behaviors were determined. Moreover, the average dipole moments of the synthesized fluorine substituted derivatives were also calculated.

KEYWORDS:

• Alkoxycyanobiphenyl
• enantiomers
• fluorine in alkoxycyanobiphenyl tail
• fluorine in LCs

Acknowledgments

We gratefully acknowledge the National Science Foundation grant DMR-1921668 for funding this project. We would also like to acknowledge Ella Wilford for her contributions to studying the phase behaviour of the mixtures, and Rohan Dharmarathna and Prof. Dr. Antal Jákli for assistance in confirming the presence of the blue phase in epoxy intermediate 9 found in Scheme 4. The computational portion of this work was supported by the National Science Foundation under grant number DMR-1921696. This work was partially performed using computational resources from the Center for Nanoscale Materials (CNM) at Argonne National Laboratory under Contract Number DE-AC02-06CH11357 with proposal numbers CNM83351 and CNM83348 and from the UW-Madison Center for High Throughput Computing (CHTC). CHTC is supported by UW-Madison, the Advanced Computing Initiative, the Wisconsin Alumni Research Foundation, the Wisconsin Institutes for Discovery and the National Science Foundation.

Disclosure statement

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

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

The work was supported by the National Science Foundation [DMR-1921696] and National Science Foundation [DMR-1921668]].