Influence of terminal substituent on non-linear S-shaped oligomers consisting of azobenzene moieties at the peripheral arm: Synthesis, characterisation and phase transition behaviour. Issue 5 (9th April 2017)

• Record Type: Journal Article
• Authors: Yeap, Guan-Yeow; Osman, Faridah; Ito, Keisuke; Takeuchi, Daisuke; Lin, Chien-Min; Lin, Hong Cheu
• Is Part Of: Liquid crystals. Volume 44:Issue 5(2017)
• Page Start: 809
• Page End: 821
• Publication Date: 2017-04-09
• Subjects: S-shaped mesogen -- monotropic -- nematic -- smectic A -- smectic B -- monolayer; Liquid crystals -- Periodicals; 548.905
• DOI: 10.1080/02678292.2016.1246677
• Languages: English
• ISSNs: 0267-8292

Abstract

ABSTRACT: A series of symmetrical S-shaped mesogens based on 4, 4′-bis-(6-bromohexyloxy)biphenyl as a central unit containing two 2-{6-[4-(4-substitutedphenylazo)phenoxy]hexyloxy}phenol as side-chain groups has been successfully synthesised. The terminal substituent was varied from halogen (X = F, Cl, Br and I) to non-halogen (X = C2 H5 and OC2 H5 ). The oligomers with C2 H5 and OC2 H5 substituents exhibit predominantly the monotropic nematic (N) phase. The OC2 H5 -containing derivatives possess long-range stability of N phase than its C2 H5 -containing analogue in which it has small range of N phase stability. As for halogen-containing analogues, oligomer with F exhibits monotropic N phase whilst oligomers with Cl and Br exhibit monotropic N and smectic A (SmA) phases. In addition, homologue with Br shows additional phase which is smectic B (SmB) phase upon further cooling. However, the oligomers in which F, Cl and Br were substituted by I exhibits purely monotropic SmA and SmB phases. X-ray diffraction measurements reveal that the smectic phase is inclined to the monolayer structure. GRAPHICAL ABSTRACT: