Abstract
A new selection of supramolecular liquid crystal complexes based on complementary molecules formed via hydrogen-bonding interactions is reported. All prepared complexes were prepared from 4-n-alkoxybenzoic acid (An) and N-4-cyanobenzylidene-4-n-(hexyloxy)benzenamine (I). FT-IR, temperature gradient NMR, Mass Spectrometer and Chromatography spectroscopy were carried out to confirm the -CN and −COOH H-bonded complexation by observing their Fermi-bands and the effects of the 1H-NMR signals as well as its elution signal from HPLC. Moreover, binary phase diagrams were established for further confirmation. All formed complexes (I/An) were studied by the use of differential scanning calorimetry and their phase properties were validated through the use of polarized optical microscopy Results of mesomorphic characterization revealed that all presented complexes exhibited enantiotropic mesophases and their type was dependent on the terminal lengths of alkoxy chains. Also, the mesomorphic temperature ranges decreased in the order I/A6 > I/A8 > I/A10 > I/A16 with linear dependency on the chain length. Finally, the density functional theory computational modeling has been carried out to explain the experimental findings. The relation between the dimensional parameters was established to show the effect of the aspect ratio on the mesophase range and stability. The normalized entropy of the clearing transitions (∆S/R) was calculated to illustrate the molecular interaction enhancements with the chain lengths.
Highlights
Supramolecular H-bonded liquid crystal complexes (SMHBLCs), which have been known for decades, began receiving more attention in the middle of the 20th Century (Fairhurst et al, 1998)
NMR Confirmations The NMR results at temperature gradient showed a significant impact on characteristic signals
The chemical shift changes towards the higher field associated with decrement of signal intensity, and indicates that the H-bonding is weakened with the temperature as expected, and this provides evidence that this part of the molecule could be subjected to conformational changes under breaking of the H-bonding
Summary
Supramolecular H-bonded liquid crystal complexes (SMHBLCs), which have been known for decades, began receiving more attention in the middle of the 20th Century (Fairhurst et al, 1998). Various SMHBLCs were documented as different kinds of H-donors and H-acceptors that offer wide many structural shapes (Ahmed and Khushaim, 2020; Al-Mutabagani et al, 2020c) These included calamitic complexes (Naoum et al, 2008; Ahmed et al, 2019a), angularshaped (Gimeno et al, 2004; Gimeno et al, 2008; Alaasar et al, 2011; Wang et al, 2015) polymeric architectures (Korkmaz et al, 2016), modular hierarchical (Pfletscher et al, 2016), nematogenic non-symmetric dimers (Korkmaz et al, 2016) or observing the twist-bend nematic mesophase (Walker et al, 2018) and supramolecular-polycatenars of chiral cubic-mesophases (Alaasar et al, 2016)
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