Synthesis, Self-assembly Behaviors And Properties Of Bi-dihydrazide Derivatives And Bi-1,3,4-oxadiazole Derivatives

Self-assembly of molecules through noncovalent interactions into various superstructures opens new possibilities of constructing novel materials in biology and materials fields. We have designed and synthesized four series twin-tapered and linear-shaped bi-dihydrazide derivatives Oxalyl acid N', N'-di(3, 4, 5-trialkoxybenzoyl)-hydrazide FH-Tn (n = 3, 4, 5, 6, 7, 8, 10), Oxalyl acid N', N'-di(4-alkoxybenzoyl)-hydrazide FH-n (n = 3, 4, 5, 6, 7, 8, 10, 16), Oxalyl acid N', N'-di(4-(2-ethylhexyloxy)benzoyl)-hydrazide FH-Z8 and linear-shaped and twin-tapered bi-1,3,4-oxadiazole derivatives 2, 2-Bis(4-alkoxyphenyl)-bi-1, 3, 4-oxadiazole BOXD-n (n = 1, 3, 4, 5, 6, 7, 10, 16) and 2, 2-Bis(3, 4, 5-trialkoxyphenyl)-bi-1, 3, 4-oxadiazole BOXD-Tn (n = 3, 4, 5, 6, 7, 8, 10, 14). The self-assembly behaviors of the FH-Tn, FH-Z8 and BOXD-Tn and BOXD-n either in solutions or in bulk were systematically investigated, and the effect of molecular structures (molecular geometry, length of the terminal chains and intermolecular interactions, etc.) on their liquid crystalline behaviors and gellation behaviors was discussed to understand the driving force for their self-assembly on molecular level. It was confirmed that bi-dihydrazide unit block can be used to construct supramolecules through self-complementary quadruple hydrogen-bonding. Electron DA interaction was demonstrated to be the driving force for the self assembly of bi-1,3,4-oxadiazole derivatives, which exhibited high. The obtained results were outlined as follows:Twin-tapered bi-dihydrazide derivatives FH-Tn were involved in intramolecular hydrogen bonding between amide groups in monomer, and there existed conformational transitions, e.g. from 6-membered rings to 5-membered rings intramolecular H-bonding upon concentrating at lower concentrations (< 255 M). Results from 1H NMR diluting experiments, FTIR spectroscopy and mass spectroscopy revealed that intermolecular H-bonds are the main driving force for the formation of supramolecular chains of FH-Tn either in chloroform at higher concentrations or in bulk. Enantiotropic columnar phases were observed in FH-Tn (n = 6, 7, 8, 10) and room temperature column hexagonal phases were obtained by air-drying the chloroform solutions of FH-T6, and FH-T7. In addition, FH-Tn (n = 3, 4, 5, 6, 7, 8, 10) are effective gelators in ethanol. The gelling ability in ethanol, the morphologies, packing structures and intermolecular H-bonding strength were significantly influenced by the length of the alkoxy chains. FH-T6 and FH-T7 showed strong gelation ability in ethanol with critical gelation concentrations of 2.1×10-3 mol L-1 and 2.3×10-3 mol L-1 respectively. Both left- and right-handed helical ribbons with non-uniform helical pitch were observed in FH-Tn (n = 5, 6, 7) gels. Linear shaped bi-dihydrazide derivative FH-Z8 with branched terminal alkyl chains self-assemblies to supramolecules through quadruple hydrogen bonds between bi-dihydrazide units and - interactions in chloroform at higher concentrations. The association constants (K) in chloroform were 2.2×103 M-1 and 1.8×103 M-1 based on NH1 and NH2 in FH-Z8, respectively, which are relatively larger than that of the twin-tapered FH-T7. FH-Z8 could gel dichloroethane with the critical gelation concentrations (CGC) of 0.14 wt%, and spontaneously crystallization from its gel upon storage at room temperature. These results suggested that bi-dihydrazide units could be used as self-complementary quadruple hydrogen-bonding units to assemble new supramolecules.Fully conjugated conformations were demonstrated either by computer simulation of BOXD-n and BOXD-Tn or in single-crystal state of BOXD-1. Well-defined 3D DA architectures with strong face-to-face and edge-to-edge donor-acceptor interactions were observed in the sing-crystal structure of BOXD-1. Nematic phase, SmC phase with large tilted angle ( 50°) and relatively large transition enthalpic values and a highly ordered SmX phase were demonstrated in BOXD-n (n = 5, 6, 7, 8, 10, 16) through tailing the terminal chains and relatively large scale monodomains were prepared in the SmX phase of BOXD-5 even without any surface treatment. Strong blue fluorescent emissions were observed in BOXD-6 either in cyclohexane ( F 92 %) or in solid state ( F 57 %). The strong donor-acceptor interaction between alkyoxyphenylene ring and 1,3,4-oxadiazole ring was thought to be the driving force for the molecules to self-assemble into large angle tilted layered structure. The columnar mesophases for BOXD-Tn (n = 5, 6, 7, 8, 10) were observed even at low temperature (-20 ) during cooling. A room temperature Colho phase was obtained for BOXD-T14. All the compounds have been demonstrated to exhibit good fluorescence properties either in cyclohexane solution or in bulk. BOXD-Tn showed monomeric feature and intramolecular charge transition at concentrations lower than 1×10-5 mol/L. Extremely strong luminescent gels and nanoparticles based on BOXD-Tn were prepared by tailing the length of the terminal chains. The xerogel of BOXD-T4 shows very strong fluorescence in the blue spectral region ( max = 423 nm) with an efficiency F up to 100 %. To the best of our knowledge, this is the strongest fluorescence quantum yield reported in solid states.BOXD-T8 molecules self-assembled to nanoparticles and further to helical nanofibers with blue fluorescence emission in DMSO, while nanoribbons which resulted in emission-enhanced gel of ethanol. The strong fluorescent emissions of BOXD-T8 in isolated state in apolar solvents were attributed to coplanar conformation of the rigid backbone and the strong fluorescent emissions of BOXD-T8 in the aggregation states were attributed to the coplanar conformation of the rigid backbone and J-aggregation. To the best of our knowledge, this is the first observation of evolution of nanoparticles to helical fibers of an achiral linear -conjugated molecule.