Novel fluorescent nanofibrous polyether template developed by SNAr polymerization of fluoroaryl-containing 1, 3, 4-oxadiazole: Photophysical properties, mesogenic phases and self-assembly

Abstract

Supramolecular organogels that respond to external stimuli have been extensively investigated; however, assembling a liquid crystal-based fluorescent gel with an efficient thermoreversible activity is a difficult challenge. Various pentafluorobenzene-containing aromatic adducts have been synthesized via nucleophilic aromatic substitution (SNAr), which is highly regio-selective to para positions. In order to prepare calamitic liquid crystals, those pentafluorobenzene-functionalized 1, 3, 4-oxadiazole aromatic adducts are a perfect choice. Novel fluoroaryl(FA)-containing 1, 3, 4-oxadiazole (Ox) main-chain polyether (PE) (FAOx@PE) were synthesized employing in situ SNAr as a practical technique for the synthesis of fluorescent liquid crystals with perfluoroaryl groups and ether bonds. The perfluoroaryl group was inserted into the 1, 3, 4-oxadiazole compound by the reaction of potassium pentafluorobenzoate and tetrazole-containing biphenyl using a DCC-assisted decarboxylating coupling. Using 1H/13C/19F NMR and FTIR spectroscopic techniques, the chemical structure of FAOx@PE was determined. Differential scan calorimeter (DSC), X-ray diffraction (XRD) and polarization microscope (POM) were utilized to examine the liquid crystal mesophases. The absorption and emission spectral patterns were detected in the ultraviolet–visible range demonstrating solvatochromic activity. Scanning electron microscope (SEM) was employed to inspect the nanofibrous morphology of FAOx@PE organogel.