Chengxiao Zhao

Photo-induced fiber–vesicle morphological change in an organogel based on an azophenyl hydrazide derivative

A new low molecular mass organic gelator (LMOG) bearing hydrazide and azobenzene groups, namely N-(3,4,5-octanoxyphenyl)-N′-4-[(4-hydroxyphenyl)azophenyl] benzohydrazide (BNB-t8), was designed and synthesized. The organogelator has shown great ability to gel a variety of organic solvents to form stable organogels with a critical gelation concentration as low as 0.5 mg mL−1. Xerogels from chloroform exhibited entangled and dense fibrous aggregates with diameters of 50–60 nm. The organogel showed photoinduced gel-to-precipitate transition under the irradiation by 365 nm UV-light, which was attributed to trans-BNB-t8 to cis-BNB-t8 photoisomerization. The trans–cisisomerization in BNB-t8 gels further caused the morphological change from fibers to vesicles at the supramolecular level.

Nanoparticles, Helical Fibers, and Nanoribbons of an Achiral Twin-Tapered Bi-1,3,4-oxadiazole Derivative with Strong Fluorescence

A twin-tapered bi-1,3,4-oxadiazole derivative (BOXD-T8) showed a monomeric feature and intramolecular charge transition at concentrations lower than 10(-5) mol/L. BOXD-T8 molecules self-assembled to nanoparticles and further to helical nanofibers with blue fluorescence emission in DMSO, while nanoribbons resulted in an emission-enhanced gel in ethanol. The strong fluorescent emissions of BOXD-T8 in an isolated state in apolar solvents were attributed to the 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.

Organogels from unsymmetrical π-conjugated 1,3,4-oxadiazole derivatives

In this study, the unsymmetrical π-conjugated gelators, 2-(3,4-bis(alkoxy)phenyl)-5-(pyridine-4-yl)-1,3,4-oxadiazole [4-POXD-Bn (n = 4, 8, 12)], were synthesized and screened for gelation in various solvents. The tendencies of the critical gelation concentration (CGC) and the gel–sol phase transition temperatures (Tgel) of the 4-POXD-B8 gels, as well as the relationship between the end-chain length of gelator and gelation ability, indicated that the solvophobic effect has a critical role in gelation. For the specific gelator that we studied, we observed that the strength of the solvophobic force was related to the solvent properties. The solvent effect on gelation was studied quantitatively using the solvent polarity parameters: polar solubility parameter (δa), dielectric constant (e), and polarity parameter (ET(30)). The results revealed that the favorable δa domain and ET(30) domain for the gelation of 4-POXD-B8 was in the range of 8.1–12.6 (cal cm−3)1/2 and 43.3–55.7 kcal mol−1, respectively. Meanwhile, a decrease of δa and ET(30) in the solvents is unfavorable for gelation. Furthermore, the solvent effect on the microstructure of the gels was studied via scanning electron microscopy (SEM). The SEM images revealed that the gels from 4-POXD-B8 in DMSO and DMF were composed of helical ribbons, whereas those formed in other solvents consisted of flat ribbons.

Kinetic and Morphological Studies of Two Different Topological Structures Developed from N, N’-Bis (4-N-Alkylo-Xybenzoyl) Hydrazine (4D16) Organogel

The compound N, N’-bis (4-n-alkylo-xybenzoyl) hydrazine (4D16), containing a dihydrazide unit in the rigid core, had been systematically investigated in view of their gelation behaviors, topological structures, and gelation formation processes. It has been demonstrated that 4D16 shows strong gelation ability in nonpolar solvents such as benzene and toluene. The xerogels consist of entangled ribbons with the width about 5 μm. According to X-ray diffraction (XRD), cubic structure is revealed in the benzene system, whereas layered structure is observed in toluene system. The morphological observations and kinetic studies by fluorescence spectroscopy as well as rheological study further reveal that self-assembly processes during gelation also differs. Radius fibers with a fractal dimension about 1.4 were observed in benzene system; whereas, less open fibrillar structures with fractal dimension approximately 1.1 were revealed for toluene system. The present results appear to represent that the molecular packing modes turn out to be solvent-dependent, which is due to unique dynamic processes.