Synthesis, characterization, and self‐assembly of fluorescent fluorine‐containing liquid crystals

Abstract

SN Ar has been used to synthesize various functionalized derivatives of pentafluorobenzenes which are highly specific at the para position; and consequently are ideal for building calamitic (rod-like) liquid crystalline molecular systems. Here, we display the effectiveness of SN Ar chemistry as a convenient method toward the synthesis of fluorescent liquid crystalline perfluorinated comprising ethers and thioethers in excellent yields and high purity. In the current work, we describe the synthesis, self-assembly, and mesogenic properties of new perfluorinated para-terphenyls bearing various para-substituted alkoxy and thioalkoxy chains. The terphenyl core was prepared using Cu(I) (or Cu(I)/phenanthroline)-catalyzed decarboxylative carbon-carbon (or carbon-oxygen [sulfur]) cross-coupling from the analogous aromatic iodide and fluorobenzoate potassium salt. The molecular structures of the prepared perfluorinated terphenyls were demonstrated with 1 H, 13 C, and 19 F NMR, as well as FT-IR and X-ray crystallography. The liquid crystalline properties and mesogenic phases were characterized with differential scanning calorimetry and high-resolution polarized optical microscope. Both UV-visible absorbance and emission spectra demonstrated solvatochromism. Supramolecular self-assembly of the generated perfluorinated para-terphenyls was monitored by van der Waals and π-π stacking interaction forces. The creation of nanofibrous architectures was monitored by scanning electron microscopy.