In situ synthesis of reduction-responsive organogelators via oxidative coupling of tritylthio-terminated gallic acid derivatives

Supramolecular organogels are semi-solid materials that have garnered tremendous interest in the past two decades due to their intriguing responsiveness to external stimuli. However, the construction of supramolecular organogels often involves inconvenient dissolution-enhancement steps such as heating and sonication, which exclude the use of heat or sonication sensitive materials and limit their applications. Herein, two tritylthioterminated gallic acid (GA) derivatives G1 and G2, which differ subtly in the length and structure of the space that links the GA unit and the trityl thiol and are incapable of gelating organic solvents at room temperature, have been developed as pre-low molecular organic gelators (pre-LMOGs) for in situ gelation at room temperature. G1 or G2 underwent oxidative coupling reaction in the presence of iodine (I-2) and turned into LMOGs without the need of a second component, leading to effective in situ gelation. Meanwhile, the in situ generated disulfide bonds confer reduction responsiveness to the formed organogels. A variety of characterizations including UV-vis absorption, transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), nuclear magnetic resonance (NMR) study, scanning electron microscopy (SEM), and theoretical calculation were employed to examine the gelation property and probe into the gelation mechanism. The difference in gelation performance of the pre-LMOGs and the in situ generated LMOGs suggests the importance of molecular flexibility in controlling the gelation behaviors. With the data, it is concluded that the gelation is driven by the collaborative contribution of multiple weak interactions, including van der Waals force, hydrogen bonding, and pi stacking interaction.