Synthesis and mesophase behaviour of Benzylidene-based molecules containing two Azomethine units

The research work involves the synthesis and characterization of intermediates 4-heptyloxybenzaldehyde (1) and 4-dodecyloxybenzaldehyde (2). Five compounds with two Schiff base linking units were further synthesized by condensation reaction using aldehyde and 1, 4-phenylenediamine. These compounds include N, N'-dibenzyliden-benzen-1, 4-diamine (3); N-benzyliden-N'-(4-chlorobenzyliden) benzen-1, 4-diamine (4); N-benzyliden-N'-(4-methoxybenzyliden) benzen-1, 4-diamine (5); N-benzyliden-N'-(4-heptyloxybenzyliden) benzen-1, 4-diamine (6) and N-benzyliden-N'-(4-dodecyloxybenzyliden) benzen-1, 4-diamine (7). These compounds were characterized using Fourier-Transform Infrared (FTIR), 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy and CHN elemental analysis. Polarized Optical Microscope (POM) was used to detect liquid crystal mesophase(s) and their thermal behaviour was measured using Differential Scanning Calorimetry (DSC). Compounds 4, 6 and 7 showed the nematic phases, while compounds 3 and 5 were found to be non-mesogenic without any liquid crystal properties

Synthesis, characterization and determination of liquid crystal properties of molecules with Schiff base linking units and cinnamaldehyde moiety

A series of liquid crystal molecules with two Schiff base linking units and a cinnamaldehyde core with different terminal groups were synthesized and characterized. The intermediates of 4- heptyloxybenzaldehyde (1a) and 4-dodeyloxybenzaldehyde (1b) were synthesized through the alkylation of 4-hydroxybenzaldehyde with a series of bromoalkane. A condensation reaction of cinnamaldehyde, 1,4- phenylenediamine and a series of substituted benzaldehydes with different terminal groups such as bromo, chloro, hydroxy, cinnamaldehyde, hydrogen, methoxy, heptyloxy and dodecyloxy produced a series of new cinnamaldehyde-based compounds, 2–9, respectively. All these compounds were characterized using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and CHN elemental analysis. The liquid crystal properties of these compounds were determined using polarized optical microscopy (POM), and their transitions were further confirmed using differential scanning calorimetry (DSC). Compounds with chloro, bromo, methoxy, heptyloxy, and dodecyloxy substituents are mesogenic compounds with nematic phase behavior. However, the other compounds were found to be nonmesogenic without any mesophase transitions