Sulfur-linked cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase |
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Authors: | Ewan Cruickshank Miros?aw Salamończyk Damian Pociecha Grant J Strachan John M D Storey Cheng Wang |
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Institution: | 1. Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Scotland, UK;2. Faculty of Chemistry, University of Warsaw, Warsaw, Poland;3. Lawrence Berkeley National Laboratory, Advanced Light Source, Berkeley, CA, USA;4. Faculty of Chemistry, University of Warsaw, Warsaw, Polandhttps://orcid.org/0000-0001-7734-3181;5. Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Scotland, UKhttps://orcid.org/0000-0002-1388-9713;6. Lawrence Berkeley National Laboratory, Advanced Light Source, Berkeley, CA, USA |
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Abstract: | ABSTRACTThe synthesis and characterisation of two series of cyanobiphenyl-based liquid crystal dimers containing sulfur links between the spacer and mesogenic units, the 4?-1,ω-alkanediylbis(thio)]bis-1,1?-biphenyl]-4-carbonitriles (CBSnSCB), and 4?-({ω-(4?-cyano1,1?-biphenyl]-4-yl)oxy]alkyl}thio)1,1?-biphenyl]-4-carbonitriles (CBSnOCB) are described. The odd members of both series show twist-bend nematic and nematic phases, whereas the even members exhibit only the nematic phase. An analogous cyanoterphenyl-based dimer, 34-{6-(4?-cyano1,1?-biphenyl]-4-yl)thio]-hexyl}11,21:24,31-terphenyl]-14-carbonitrile (CT6SCB), is also reported and shows enantiotropic NTB and N phases. The transitional properties of these dimers are discussed in terms of molecular curvature, flexibility and biaxiality. The same molecular factors also influence the birefringence of nematic phases. Resonant X-ray scattering studies of the twist-bend nematic phase at both the carbon and sulfur absorption edges were performed, which allowed for the determination of critical behaviour of the helical pitch at the transition to the nematic phase, the behaviour was found to be independent of molecular structure. It was also observed that despite the different molecular bending angle and flexibility, in all compounds the helical pitch length far from the N-NTB transition corresponds to 4 longitudinal molecular distances. |
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Keywords: | Twist-bend nematic phase liquid crystal dimers birefringence sulfur linked cyanobiphenyl resonant X-ray scattering |
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