Gelation And Liquid Crystalline Behaviour Of Dihydrazide Derivatives

Supramolecular liquid crystals and low molecular-mass organic gels arefascinating organized soft material, depending on the noncovalent interactions,including hydrogen bonding, π-π stacking, donor–acceptor interactions,hydrophobic forces, metal coordination and van der waals interactions. Hydrogenbonds are one of the most important interactions in the self-assembly of moleculesbecause of their strength, directionality, reversibility, and selectivity, which has beenutilized to build supramolecular architectures consisting of amino acid, amide, urea,hydrazine, sugar or steroid groups.In this context, as part of our continuing research on amide and hydrazide insupramolecular self-assembly, we report the preparation and self-assemblybehaviour of three new series of compounds derived from dihydrazide derivatives,T7series (T7-ben, T7-fuma, T7-mal), B8series(B8-fuma and B8-but), B8b series(B8b-fuma, B8b-but, B8b-ben, B8b-hex), which aimed to investigate the differentcentral linking units how to effect the liquid crystal and gel behaves. Thesediscoveries of T7series were examples of the continuing effort to explore the limitsof molecular structures compatibility with self-assembly behaviour. The obtainedresults were outlined as follows:1) Three novel classes of dihydrazide derivatives have been synthesized, namely T7sereis (T7-ben, T7-fuma, T7-mal), B8sereis (B8-fuma, B8-but) and B8b sereis (B8bfuma, B8b-but, B8b-ben, B8b-hex).1H NMR, FTIR and elemental analysis were employed to confirm their molecular structures.2) T7-ben and T7-fuma were belong to twin-tapered molecules, while T7-mal couldbe viewed as two tapered molecules. The mesomorphic behavior of T7-series wasinvestigated by polarizing optical microsopy (POM), differential scanningcalorimetry (DSC), and X-ray diffraction (XRD), finding that T7-ben exhibited anenantiotropic rectangular columnar phases, while T7-mal showed a simple cubicmesophase, T7-fuma decomposed at259℃.3) Temperature-dependent1H NMR and FT-IR spectroscopic experiments wereperformed for T7series to confirm the primary involvement of N-H protons inintermolecular hydrogen bonding at room temperature; which were further existingsupported by the fact that the N-H stretching vibration band and amide I bondbecame weaker and shifted to higher frequencies upon heating. Even in liquidcrystal phase intermolecular hydrogen bonds still remained. There are someinteraction between C=C double bonds of T7-fuma. Compared with the T7-ben,the steric hindrance of T7-fuma with ethene group as central linking units decreased.So T7-fuma has the strongest intermolecular hydrogen bonding among the T7series.4) The gelation abilities of T7fuma were tested in23carefully selected organicsolvents at room temperature and19solvents could form gel and4solvent wereinsoluble, which could considered as supergelator with lower CGC and higher Tg.The self-assemble behaves were investigated by SEM, XRD, UV-vis, fluorescence,contact angle, rheological measurements in apolar solvent toluene and polar solventethanol. The transparent gel was formed in toluene, which consisted of fibers of80-100nm in width and tens of micrometers in length, which further entangled tothree-dimensional networks showing homogeneous density. In contrast, gel inethanol consisted of fibers with similar width, while shorter in length comparing tothose of toluene gel and tending to tangle. In addition, the fibers from ethanol gelwere denser and thicker than those of toluene gel. The gels in ethanol showedstronger rheological properties than those in toluene because of some large tangledknot; at the same time, the xerogel of ethanol formed superhydrophobic interface with contact angle158°because of rougher surface; aggregation-induced emission(AIE) has been observed after gelation in ethanol, while dilute toluene solution(3×10-6mol/L) excited stronger fluorescence because of more planar structure, inwhich two weak peaks of aggregation was found, which provided that T7fuma hadpoor solubility in toluene and tended to aggregate even in dilute solution.5） We investigated how the Hansen solubility parameters were made to understandthe effect of solvent on the gelators in quantitative way. We further attempted torationalize the gelation test data by using a teas plot derived from teas parameters, inwhich gelation domain was marked, these results show that the above method maybe used to estimate the gelling ability of various types of gelators, based on theirbehaviour in a limited set of solvents.