RESUMEN
A new class of bisurea derivatives bearing tetrahydroxy groups have been proven to be non-gelators in water and various organic solvents even under long-term sonication or efficient heating treatment. We found that it is possible to trigger physical gelation behaviour by constructing dynamic covalent bonding. The results show that formation of dynamic covalent bonding between the borate anion and ethanediol substituent in these bisurea derivatives brings about rapid physical gelation at ambient temperature in a mixture of DMSO and water. During dynamic covalent bonding-triggered gelation, the stepgrowth polymerization from the B-O bonds would increase the size of the molecules and reduce the entropy of mixing as well as facilitate ion-dipole interactions in the linear polymeric gelators. They would drive a self-assembly transition and boost the construction of gel networks in coordination with α-tape urea-urea hydrogen bonding. The gelation mechanism was explored by 1H NMR, FTIR and rheology techniques. Moreover, the resulting gels are transparent and thixotropic, and could be turned into the sol state under CO2 or water-stimulus. Furthermore, they are stable in the presence of HAuCl4 and alkali. Therefore, they would afford another new medium for the growth of Au nanocrystals via in situ reduction and a new sensing medium for detecting Hg2+ ions.
RESUMEN
Physical gelation behaviors of a series of novel bisurea-based derivatives bearing fatty alkyl tertiary amine moieties have been explored in water and common organic solvents. One of these amines exhibits very good thixotropic gels in apolar aromatic solvents (e.g., xylenes). The corresponding sol-gel transition is instantaneous and could be repeated for at least 50 cycles. Interestingly, the elasticity and strength of the resulting gels can be remarkably enhanced initially by the addition of a trace amount of tetrabutylammonium acetate (TBA) followed by a subsequent drop with further salt addition. Temperature-dependent 1H NMR confirmed that hydrogen bonding is the main driving force for the physical gelation. TEM, rheology, 1H NMR titration, and examination of critical gelation concentration (CGC) reveal that the phenomenon is due to the dominated effects, the salting out effect at lower TBA concentration, or the anion-urea hydrogen bonding at higher TBA concentration. Furthermore, the obtained transparent gels in this work can be used as good media for growing crystals of several organic semiconductors.
RESUMEN
As a superstar organic semiconductor, fullerene (C60 ) is versatile in nature for its multiple photoelectric applications. However, owing to its natural 0D structure, a challenge still remains unbeaten as to growth of 1D fullerene crystals with tunable sizes. Herein, reported is an efficient approach to grow C60 as super-long crystalline fibers with tunable lengths and diameters in supramolecular gel by synergic changes of anti-solvent, gel length, crystallization time or fullerene concentration. As a result, the crystalline C60 fibers can be modulated to as long as 70 mm and 70 000 in their length-to-width ratio. In this case, the gel 3D network provides spatial confinements for the growth of 1D crystal along the directional dispersion of anti-solvent. The fabricated fullerene device exhibits high responsivity (2595.6 mA W-1 ) and high specific detectivity (2.7 × 1012 Jones) at 10 V bias upon irradiation of 400 nm incident light. The on/off ratio and its quantum efficiency are near to 540 and about 800%, respectively, and importantly, its photoelectric property remains very stable after storage in air for six months. Therefore, spatially confined growth of fullerene in supramolecular gels will be another crucial strategy to synthesize 1D semiconductor crystals for photoelectrical device applications in near future.