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 TT-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 gets in mixtures of water with DMSO, alcohols, acetone, and DMF. Scanning electron microscopy revealed high-aspect-ratio fibers, and Raman spectroscopy confirmed that the Pi-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 get is also formed at room temperature when DMSO/H2O is added after the reaction of I with a weaker oxidant (nitric oxide).