Synthesis and characterization of novel fluoroterphenyls: self-assembly of low-molecular-weight fluorescent organogel

Abstract

Nucleophilic aromatic substitution has been highly para selective on a range of functionalized pentafluorobenzenes. Here, we demonstrate the utility of nucleophilic aromatic substitution chemistry for the preparation of fluorinated fluorescent low-molecular-weight organogels. The molecular design, synthesis and photophysical performance of a new class of thermoreversible and fluorescent low-molecular-weight organogels from para-alkoxy-functionalized fluorinated terphenyls are described. Both CuI-catalyzed decarboxylative cross-coupling and nucleophilic aromatic substitution chemistry were used for the preparation of those highly fluorinated gelators in high yields and excellent purity via simple filtration, from the corresponding potassium fluorobenzoate salts and aryl iodides. Various fluorinated symmetrical and asymmetrical para terphenyls were prepared with various para terminal alkoxy tails. Those fluorinated terphenyls were characterized using X-ray crystallography, differential scanning calorimetry, Fourier-transform infrared spectroscopy, as well as ¹ H, ¹³ C, and ¹⁹ F nuclear magnetic resonance. UV-visible light absorbance and emission spectra of those new materials displayed a solvatochromic and solvatofluorochromic behaviour, respectively. Self-assembly of the produced fluorinated terphenyls occurred via cooperative π-π stacking and van der Waals interactions, which resulted in gelating various organic solvents. Scanning electron microscopy displayed the formation of fibre-like nanostructures. The cytotoxicity of some selected fluorinated symmetrical and asymmetrical para terphenyls was explored.

Keywords: decarboxylative cross-coupling; fluorescence; nucleophilic aromatic substitution; organogel; perfluorinated terphenyl.