Soft Ionic Diode Fabricated Using Asymmetric Ion Distribution in Li+-Zn(II)/Cu(II) Metallohydrogels.

The development of metal ions-incorporated soft materials is of great importance in the present scenario due to their essential requirement in the fabrication of the components such as ionic diodes and electrochemical transistors for soft electronic devices. In the current work, to fabricate a soft ionic diode, two distinct Li+-driven conductive metallohydrogels, namely, MG-Zn and MG-Cu, have been obtained by individually treating a LiOH deprotonated pregelator (H5APL) with Zn(OAc)2 or Cu(OAc)2. The pregelator and metallohydrogels have been well characterized by using various instrumental techniques, which supports their proposed formulations. Field emission scanning electron microscopic images of metallohydrogels reveal the presence of a fibrous network, which helps to create a gel matrix, whereas the rheological experimental results ascertain the true gel phase nature of the synthesized metallohydrogels. The obtained MG-Zn and MG-Cu metallohydrogels were subjected to electrochemical impedance spectroscopic and band gap measurements. The MG-Zn and MG-Cu showed ionic conductivities of 1.02 × 10-3 and 1.14 × 10-3 S/cm, along with band gaps of 2.82 and 2.85 eV, respectively, thus claiming their suitability for device fabrication. Further, the fabricated metallohydrogel-based ionic diode shows appreciable ability to rectify the ionic current with the forward and reverse bias currents of 19 and 1.9 mA at +/-4 V bias potential. Based on all the experimental results, the mechanism has been well established for the rectification behavior in the fabricated metallohydrogel ionic diode.

A Li+-integrated metallohydrogel-based mixed conductive electrochemical semiconductor.

A metallohydrogel (STG)-based mixed conductive electrochemical semiconductor has been obtained via LiOH-deprotonation of a pre-gelator (H4STL) followed by treatment with Cd(OAc)2. The gelation mechanism of STG, its mixed ionic-electronic conductive nature and application towards an electrochemical semiconductor were well explored by using various techniques including EIS studies.

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

A fluorescent metallogel (2.6 % w/v) has been obtained from two non-fluorescent components viz. phenyl-succinic acid derived pro-ligand H2 PSL 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, 1 H NMR, fluorescence and ESI-MS.

An Li+-enriched Co2+-induced metallogel: a study on thixotropic rheological behaviour and conductance.

An alkali base and counterion-selective red metallogel (1% w/v) has been synthesized by mixing the adipic acid-derived ligand H2AL with LiOH, followed by the addition of 1 equivalent of Co(OAc)2 in DMF. The addition of Co(OAc)2 not only resulted in the formation of a 2 : 2 (M : L) complex, but also led to the consecutive steps of aggregation, fiber creation, entrapment of the solvent and eventually gelation. The metallogel formation and the mechanism behind gelation have been well characterized and established using various instrumental techniques such as FTIR spectroscopy, UV-vis spectroscopy, FE-SEM, TEM, PXRD, ESI-mass spectrometry, Job's plot and rheology analysis. Nyquist plots suggested a large decrease in the resistance value from 11.3 kΩ to 4.2 kΩ for the solution obtained from the ligand deprotonated by LiOH (AL2-) and Co(OAc)2 containing the metallogel. The Nyquist plot and resistance of the metallogel have also been studied under the influence of temperature and ultrasound stimuli. The extensive rheological measurements provide information about the strength of the gel network and the highly reversible nature and thixotropic behaviour of the metallogel.