Chirality-Induced Liquid Crystalline Properties of Seven-Ring Trimeric Mesogens Incorporating Dual Chiral Centers

Abstract

Two series of novel trimers with benzylidene-1,4-phenylenediamine core units attached by two (S)-2-methylbutyl 4-(4′-phenyl)benzoate moieties via methylene groups at terminal ends have been synthesized and characterized. In each series, the title compounds differ from each other in term of spacers -OC_nH_2nO- wherein n ranges from 5 to 12. The difference of the second series from their analogues in the first series is due to the presence of two OCH₃ groups residing at the meta position in the benzylidene-1,4-phenylenediamine mesogenic core. The trimers without lateral OCH₃ groups exhibit the SmC* and SmA phases in addition to the N* phase suggesting the possession of high molecular shape anisotropy. The higher-order tilted smectic phases and the blue phase are also observed for the members with odd n numbers in the first series. In the second series, however, the smectogenic characteristics are absent. Whilst the even-parity trimers are nematogenic, the trimers with odd spacers are not mesogenic. The trimers without lateral OCH₃ groups in the first series also exhibit higher mesophase thermal stability in comparison with their analogues in the second series.

ACKNOWLEDGMENTS

The main author (G.-Y. Yeap) acknowledges the Malaysian Higher Education Ministry and the Ministry of Science, Technology and Innovation (MOSTI) for the financial support in terms of research grants (Fundamental Research Grant Scheme, Account No. 203/PKIMIA/671025 and eScience, Account No. 305/PKIMIA/613315). The authors are also grateful to Professor Corrie T. Imrie from the University of Aberdeen, Scotland for his helpful comments and discussion regarding this work.

Notes

^a Denotes transition temperatures determined via polarizing microscopy, undetected via DSC.

^b Denotes transition temperatures and enthalpies derived from unresolved peaks.

^c Denotes SmX = SmF* for compound 5c.

^d Denotes SmA-SmC*-SmX transition temperatures upon cooling which are not well resolved.

[] Denotes transition temperatures in formation of monotropic SmX, SmF* or SmC*, phase.

^a Denotes transition temperature determined via polarizing microscopy, undetected via DSC.