Synthesis and self-assembly of new fluorescent cholesteryloxy-substituted fluorinated terphenyls with gel formation and mesogenic phases

Abstract

Fluorescent mesogenic compounds have been reported as suitable materials for electronic displays with low energy consumption. Aromatic nucleophilic substitution (SNAr) reactions have been extremely para selective on various pentafluorophenyl derivatives, which is ideal to build up fluorescent calamitic (rod-like) liquid crystals. In the current study, we report the use of SNAr strategy toward the synthesis of emissive low molecular mass organogels (LMMOs) with mesogenic phases. The synthesis of these new cholesteryloxy-substituted fluorinated terphenyls was carried out through decarboxylative cross-coupling reaction catalyzed by copper iodide, followed by the application of SNAr chemistry. The produced organogelator was obtained in excellent purity and high yield starting from aryl iodides and pentafluorobenzoate. A series of asymmetric fluorinated terphenyls were synthesized with different terminal alkoxides. The molecular structures were studied by elemental analysis, 1H, 13C and 19F NMR, and infrared spectroscopic methods. The liquid crystalline phases were explored by differential scan calorimeter (DSC) and optical polarizing microscopy (POM) demonstrating at least one mesogenic phase. The absorbance and fluorescence spectral curves exhibited solvatochromic properties. The morphological properties were studied by scan electron microscope (SEM), which showed nanofibrous scaffolds generated from the assembly of cholesteryloxy-substituted terphenyls. This self-assembly process was supported by π-stack packing and van der Waals forces.