Molecular organization and molecular order of two rod-like smectogens in mesophases

ABSTRACT

Structurally simple two rod-like mesogens with a three-ring core consisting of biphenyl and phenyl rings are synthesised to investigate the mesophase properties, molecular organisation and the orientational order parameter. In mesogen-1, a dodecyloxy terminal chain is present on the biphenyl ring while the phenyl ring is free from substituent. For mesogen-2, in addition to the dodecyloxy chain, the butyl chain is placed on the phenyl ring. The Hot-stage optical polarising microscopy (HOPM) and differential scanning calorimetry (DSC) measurements show smectic A (SmA), smectic B (SmB), and crystal E (CryE) phases for mesogen-1 and SmA, smectic C (SmC) and smectic F (SmF) phases for mesogen-2. The presence of smectic mesophases is established by X-ray Diffraction (XRD). 1D and 2D ¹³C solid-state NMR experiments are performed in smectic mesophases to find the orientational order parameters of the phenyl rings of the core. The main order parameter (S_zz) of the mesogens in the SmB and SmF phase is in the range of 0.87–0.93. The excellent spectral resolution noticed in ¹³C NMR spectra in the SmB mesophase (mesogen-1) indicates that the internal rotations of the molecules along the long axis are primarily unhindered.

GRAPHICAL ABSTRACT

KEYWORDS:

• Smectic
• biphenyl
• ¹³C NMR
• ¹³C-¹H dipolar couplings
• order parameter
• XRD

Acknowledgements

The CSIR-CLRI authors thank Dr. K. J. Sreeram, Director, CSIR-CLRI, for his support. Authors acknowledge Prof. K. V. Ramanathan, Indian Institute of Science, Bangalore for discussions. A.A.B. thanks the financial support from the Council of Scientific and Industrial Research (CSIR), New Delhi, in the form of a Senior Research Fellowship. CSIR-CLRI Communication No. 1794.

Disclosure statement

No potential conflict of interest was reported by the author(s).