Phase transitional behaviour of S-shaped oligomers incorporating biphenylene and cholesterol entities. Issue 5 (9th April 2017)

• Record Type: Journal Article
• Authors: Osman, Faridah; Yeap, Guan-Yeow; Maeta, Nobuyuki; Ito, Masato M.; Lin, Chien-Ming; Lin, Hong-Cheu
• Is Part Of: Liquid crystals. Volume 44:Issue 5(2017)
• Page Start: 822
• Page End: 832
• Publication Date: 2017-04-09
• Subjects: Symmetrical S-shaped -- liquid crystalline properties -- outer spacers -- enantiotropic -- monotropic -- odd–even effect; Liquid crystals -- Periodicals; 548.905
• DOI: 10.1080/02678292.2016.1247477
• Languages: English
• ISSNs: 0267-8292

Abstract

ABSTRACT: A new series of symmetrical S-shaped oligomers 4, 4′-bis[(5-cholesteryloxycarbonylpentyl alkoxy)hexyloxy]biphenyl consisting of outer spacers –(COCH2 ) n – as well as an inner spacer –(CH2 )6 – has been synthesised. Their liquid crystalline properties and phase transition temperatures with associated enthalpy changes are recorded. The outer spacers are varied from n = 5–8 to 10 and 11. The compounds with even spacer exhibit enantiotropic phase and oligomers with odd parity display monotropic phase. The oligomers with odd membered n = 5, 7 and 11 exhibit N* and SmC* phases upon cooling. Whilst upon heating, the homologues with even-numbered member n = 6 and 10 show N* phase and upon cooling, both compounds exhibit N* and SmC* phases. However, oligomer with outer spacer n = 8 displays enantiotropic N* and SmC* phases. The temperature range of N* phase for even and odd membered decreased as the outer spacers are increased. The odd–even effect has been found in the I–N* transition temperatures where the odd-parity oligomers exhibit lower values when compared to compounds of an even-parity series. The X-ray diffraction measurements reveal the appearance of SmC* phase that can be associated with the monolayer ordering of these oligomers. GRAPHICAL ABSTRACT: