Thermotropic liquid–crystalline properties of 4,4′-dialkoxy-3,3′-diaminobiphenyl compounds and their precursors

ABSTRACT

A series of 4,4ʹ-dialkoxy-3,3ʹ-diaminobiphenyl compounds were synthesised by three-step procedure that involves alkylation, nitration and reduction reactions. Their chemical structures were characterised by FTIR, ¹H and ¹³C spectroscopy and elemental analysis. Their thermotropic liquid–crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VT-XRD). The 4,4ʹ-dialkoxy-3,3ʹ-dinitrobipheyl compounds, precursors to the diamine compounds, were also examined for their thermotropic LC properties. POM studies of focal conic textures and VT-XRD of the 3,3ʹ-diaminobiphenyl derivatives having flexible alkyl chains (C₆–C₁₂) exhibited the smectic A (SmA) phase independent of the length of alkyl chains. Similarly, the 3,3ʹ-dinitrobiphenyl derivatives containing alkyl chains C₇, and C₉–C₁₁ exhibit the SmA phase, those containing C₈ formed the smectic C (SmC) phase and C₁₂ formed both the SmA and smectic B (SmB) phases, respectively. The 3,3ʹ-diaminobiphenyl derivatives had excellent thermal stability in the temperature range of 237–329°C, while those of 3,3ʹ-dinitrobiphenyl derivatives were in the temperature range of 270–321°C. The 3,3ʹ-diaminobiphenyl derivatives emitted UV light both in chloroform and acetonitrile.

Graphical Abstract

KEYWORDS:

• Liquid–crystalline
• polarising optical microscope
• thermotropic
• X-ray
• diffraction
• smectic A phase
• smectic C phase
• synthesis
• differential
• scanning calorimetry

Acknowledgements

We thank Dr. Bidyut Biswas and Cynthia Wade for the synthesis of some compounds. We also thank an anonymous reviewer for valuable suggestions and comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

We (T.H., M.R.F, D.M.A-K., L.S. and S.K.) at the Kent State University acknowledge the support from NSF under the US Ireland R&D Partnership under Award # DMR-1410649. The work at the University of Nevada Las Vegas is supported, in part, by the NSF [grant number. 0447416 (NSF EPSCoR RING-TRUE III)], NSF-SBIR [grant number OII-0610753], NSF-STTR [grant number IIP-0740289], and NASA GRC Contract No. NNX10CD25P.