Synthesis and optics properties of fluorinated pyrrole diphenly liquid crystals

A series of new Liquid crystals (LCs) based on fluorinated pyrrole derivatives as skeleton was designed. The key intermediate, 3, 4-difluoro-1-(4-iodophenyl)-1H-pyrrole was prepared by cyclization, dehydrofluorination arylation procedure. The intermediate was treated by formylation, dehydration and cyaniding reaction to yield 3,4-difluoro-1-(4-iodophenyl)-1H-pyrrole-2-carbonitrile. Further, these pyrrole derivatives coupled with substituted phenylboronic acid by Suzuki coupling reaction to give the target products. These new molecules were characterized by Nuclear magnetic resonance ( 1H NMR，19F NMR), Mass spectrum (MS), high resolution mass spectrometry (HRMS) or Elemental analysis (EA). Their liquid crystal phases were investigated by Polarizing optical microscope (POM) and Differential scanning calorimeter (DSC). Thermal stabilities were determined by Thermal gravimetric analysis (TGA). The absorption and photoluminescence spectra of these compounds were analyzed by UV/Vis. These new molecules exhibit typical mesomorphic behaviors and good thermal stability. Compounds with cyano group on the fluoropyrrole display stronger fluorescence intensity. Based on theoretical calculations, the fluorinated compounds have the larger dipole moments, which is in favour of improving the dielectric anisotropy. As a serious of new liquid crystal building blocks, these pyrrole derivatives substituted by fluorine atoms and cyano groups provided experimental basis for synthesis of large dipole moment molecules of liquid crystals in the future.