Investigation of the Mechanism Behind Conductive Fluorescent and Multistimuli-responsive Li+-enriched Metallogel Formation

Abstract

A fluorescent metallogel (2.6 % w/v) has been obtained from two non-fluorescent components viz. phenyl-succinic acid derived pro-ligand H2PSL and LiOH (2 equiv.) in DMF. Li+ ion not only plays a crucial role in gelation through aggregation, but also contributed towards enhancement of fluorescence by imposing restriction over excited state intramolecular proton transfer (ESIPT) followed by origin of chelation enhanced fluorescence (CHEF) phenomenon. Further, the participation of CHEF followed by aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) in the gelation process have been well established by fluorescence experiments. Transmission electron microscopy (TEM) analysis disclosed the sequential creation of nanonuclei followed by nanoballs and their alignment towards the generation of fibers of about 3, 31 and 40 nm diameter, respectively. The presence of a long-range fibrous morphology inside the metallogel was further attested by scanning electron microscopy (SEM). Rheological studies on the metallogel showed its true gel-phase material nature. Nyquist impedance study shows a resistance value of 7.4 kΩ for the metallogel which upon applying ultrasound increased to 8.5 kΩ, while an elevated temperature of 70 °C caused reduction in the resistance value to 4.8 kΩ. The mechanism behind metallogel formation has been well established by using FTIR, UV-vis, SEM, TEM, PXRD, 1H NMR, fluorescence and ESI-MS.