Synthesis and Liquid-Crystalline Properties of β-Bromopentakis(Alkoxy) Triphenylene: Reactivity of VOCl₃, MoCl₅, and FeCl₃ as Oxidants

Abstract

We present a simple synthetic strategy leading to nonsymmetrical functionalized hexasubstituted triphenylene. Further, new β-bromopentakis(alkoxy)triphenylene was synthesized applying this strategy and reactivity of oxidizing agents such as VOCl₃, MoCl₅, and FeCl₃ was investigated. The liquid-crystalline properties were studied by polarizing optical microscope (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) studies. The higher homologues exhibit a columnar hexagonal (Col_h) phase, whereas lower homologues also exhibit a columnar hexagonal plastic (Col_hp) phase. These mesophases are stable below and above the ambient temperature. We studied the effect of polar substitution on molecular self-assembly and found that a bromo bulky substituent at the β-position of pentakis(alkoxy)triphenylenes stabilized the intra- or intermolecular interaction between the cores to form columnar mesophases.

Keywords:

• Columnar
• columnar hexagonal plastic
• discotic liquid crystals
• oxidative coupling
• triphenylene

Acknowledgment

S. K. Varshney is grateful to Prof. K. A. Suresh for his sustaining support for the research work and to Dr. Veena Prasad for the fruitful discussions. A fellowship by the Japan Society for Promoting Science (JSPS), Tokyo, Japan, is gratefully acknowledged.

Notes

Cr = crystal; Col_h = columnar hexagonal; Col_hp = columnar hexagonal plastic; g = glassy transition; I = isotropic liquid.

Temperatures are given in °C and enthalpies (in parentheses) are given in kJ mol⁻¹.