Thermal and nonlinear optical studies of newly synthesized EDOT based bent-core and hockey-stick like liquid crystals

Abstract

Novel EDOT based bent-core and hockey-stick shaped mesogens bearing terminal alkyl chains and alkoxy terminal chains, respectively, have been designed and synthesized via the Sonogashira coupling reaction. Molecular structures of these new compounds were determined using spectral and elemental analysis. The mesomorphic behaviour of all the novel compounds was primarily investigated by a combination of polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies (XRD). All of the compounds exhibit an enantiotropic nematic phase in lower homologs. However, a smectic A phase at a lower temperature along with the high temperature nematic phase was observed in higher homologs of BC and hockey-stick LCs. A density functional theory study was carried out to investigate the stable configuration. The bent angle of these molecules was intermediate between calamitic LCs and banana LCs. The photophysical properties of all the compounds were studied in anhydrous chloroform solvent and show absorption patterns around 370–395 nm and emission between 418–465 nm. We have also reported large effective two-photon absorption in these novel compounds when measured under excitation by nanosecond laser pulses at 532 nm. All of the mesogenic compounds are nonlinear materials, which make them suitable candidates for optical limiting applications.