Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis, mesomorphism and emission properties

ABSTRACT

A series of flexibly linked bis(pyridinium) salts with various counterions (Br⁻, PF₆⁻, BF₄⁻ and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl = dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Col_h) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Ionic liquid crystals
• columnar hexagonal
• pyridinium
• emission

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by a grant of the Romanian Authority for Scientific Research, CNCS-UEFISCDI [project number PN-II-ID-PCE-2011-3-0384].