Liquid crystalline alkyl-substituted oligo(p-phenyleneethynylene)s: synthesis and structure-property relationships

• Published in: Liquid crystals Vol. 39; no. 3; pp. 269 - 284
• Main Authors: Yatabe, Tetsuo, Kawanishi, Yuji
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 01.03.2012; Taylor & Francis Ltd
• Subjects: Chemical synthesis; Crystal structure; Derivatives; Differential scanning calorimetry; Liquid crystal polymers; liquid crystalline conjugated oligomers; Liquid crystals; mesomorphic properties; Mesophase; Molecular structure; molecular structures; oligo(p-phenyleneethynylene)s; Phases; structure-property relationships; Terminals; Transition temperature
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678292.2011.637135

A new series of liquid crystalline oligo(p-phenyleneethynylene)s, namely laterally and terminally alkyl-substituted derivatives of phenyl-terminated phenyleneethynylene hexamer (H(C 6 H 4 CC) 6 C 6 H 5 ), were synthesised, and the relationships between molecular structures and mesomorphic properties were investigated. The mesomorphic properties of the hexamer derivatives were examined by differential scanning calorimetry and polarising microscopy. In the alkyl-substituted hexamer derivatives, R 1 C 6 H 4 CC[C 6 H 2 (R 2 ) 2 CC][C 6 H 2 (R 3 ) 2 CC][C 6 H 2 (R 4 ) 2 CC][C 6 H 2 (R 3 ) 2 CC][C 6 H 2 (R 2 ) 2 CC]C 6 H 4 R 1 , where R 1 , R 2 , R 3 and R 4  = alkyl chains of various lengths or H, most of the hexamer derivatives exhibited nematic phases, whereas the others did not show any mesophases. It was found that the formation of the mesophase and the crystalline-nematic and nematic-isotropic transition temperatures were strongly affected by the length, number and position of the lateral chains, and by the length of the terminal chains.