Analyte-Triggered Gelation: Initiating Self-Assembly via Oxidation-Induced Planarization

An alternative design strategy for inventing new triggered gelations was tested. Single crystal X-ray diffraction confirmed that an oxidation can convert a nonplanar dihydropyridine ( 1 ) that exhibits weak 1-D intermolecular interactions into a planar pyridine ( 2 ) that exhibits significant 1-D π-stacking interactions. Moreover, an electron-rich aryl ethynylene substituent was used to enhance the self-assembly process through donor−acceptor interactions. Pyridine 2 was discovered to form gels in mixtures of water with DMSO, alcohols, acetone, and DMF. Scanning electron microscopy revealed high-aspect-ratio fibers, and Raman spectroscopy confirmed that the π-stacking direction is coincident with the fiber axis. Gelation was induced at room temperature by adding a strong oxidant (cerium(IV) ammonium nitrate) to a solution of 1 . A gel is also formed at room temperature when DMSO/H 2 O is added after the reaction of 1 with a weaker oxidant (nitric oxide).