Structure property and mesomorphic behaviour of S-shaped liquid crystal oligomers possessing two azobenzene moieties

ABSTRACT

A new series of symmetrical S-shaped oligomers 4,4ʹ-bis(ω-2-(ω-[(bromophenyl)diazenyl]-alkoxy)phenoxy)hexylbiphenyl consisting of two different spacers (inner -(CH₂)₆- and outer -(CH₂)_n-) have been synthesised. Their physical, thermal and texture observation over various transition temperatures are reported. The outer spacers for these compounds vary from n = 4 to n = 9. The oligomers with even number of members exhibit monotropic phase in which the compound with n = 4 shows nematic (N) phase whilst those with members n = 6 and 8 exhibit N and smectic A (SmA) phases. However, the homologs with odd number of members display enantiotropic phase in which the compound with n = 5 exhibits N and smectic phases whereas the members with n = 7 and 9 are predominantly smectogenic. The temperature range of N phase for even-numbered member decreased with elongation of the outer spacer. The smectic phase stability among the members in the present series increases when the outer spacer n is increased from 5 to 8.

Graphical Abstract

KEYWORDS:

• Symmetrical S-shaped
• mesomorphic behaviour
• monotropic
• enantiotropic
• outer spacer

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The main author (G.-Y. Yeap) would like to acknowledge Universiti Sains Malaysia for funding this project through RU [grant number 1001/PKIMIA/811223]. F. Osman also wishes to thank the MOHE for the scholar assistantship under the MyBrain15 scheme.