Non-linear disulphide-centred S-shaped oligomers containing inner and outer spacers with lateral Schiff base: synthesis and mesomorphic properties

• Published in: Liquid crystals 2024-09, Vol.51 (12), p.2081-2093
• Main Authors: Yap, Pui-Wing, Yeap, Guan-Yeow, Oo, Chuan-Wei, Wan Abdullah, Wan Nazwanie, Shichibu, Yukatsu, Konishi, Katsuaki
• Format: Article
• Language: English
• Subjects: central disulphide; Crystallization; DFT; Disulfides; Imines; Molecular structure; Non-linear; odd-even effect; Oligomers; photoisomerisation; Transition temperature; Transition temperatures
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678292.2024.2386579

A new series of non-linear S-shaped oligomers [bis-6-(2-((4-methoxyphenyl-imino)methyl)-5-(4'-hexyloxy-4-biphenyloxycarbonyl)-phenoxy)alkyl]disulphide have been synthesised and characterised. The present oligomers consist of a central disulphide (S-S) linkage, Schiff base, outer alkyl spacer (n 1 = six carbons) and inner alkyl spacer (n 2 = six to eleven carbons). Upon cooling, all the oligomers show monotropic nematic phase. The odd-even effect was found at the transition temperature of Cr-I (T Cr-I ) and temperature range from isotropization to crystallisation (∆T I-Cr ). However, the odd-even effect was not observed at the transition temperatures of I-N and N-Cr as the values decrease when n 2 increases. The representative oligomer with n 2  = 7 undergone photoisomerisation behaviour and completed the conversion from trans to cis within a duration of 13 mins and vice versa (up to 1200 min). Optimized molecular structures of oligomers with n 2  = 6 and 7 were obtained from TMoleX, and their length-to-breadth ratio can be reasonably employed to explain the odd-even effect in T Cr-I , ∆T I-Cr and the reduction of its values in entropy change (∆S I-N /R).