Adipic acid directed self-healable supramolecular metallogels of Co() and Ni(): intriguing scaffolds for comparative optical-phenomenon in terms of third-order optical non-linearity

Two brilliant outcomes of supramolecular self-assembly directed, low molecular weight organic gelator based self-healable Co( ii ) and Ni( ii ) metallogels were achieved. Adipic acid as the low molecular weight organic gelator and dimethylformamide (DMF) solvent are employed for the metallogelation process. Rheological analyses of both gel-scaffolds reveal mechanical toughness as well as visco-elasticity. Thixotropic behaviours of both the gels were scrutinized. Morphological variations due to the presence of two different metal ions with diverse metal-ligand coordinating interactions were established. The mechanistic pathways for forming stable metallogels of Co( ii )-adipic acid (Co-AA) and Ni( ii )-adipic acid (Ni-AA) were judiciously developed through infrared absorption spectral analysis. The nonlinear optical properties, such as the third-order process, of these synthesized metallogels were scrutinized by means of the Z -scan method at a beam excitation wavelength of 750 nm by a femtosecond laser with different excitation intensities ranging from 64 to 140 GW cm −2 . The third-order nonlinear optical susceptibility ( χ (3) ) of the order of 10 −14 esu was obtained from the measured Z -scan data. Both the metallogels exhibit positive nonlinear refraction and reverse saturable (RSA) absorption at high-intensity excitation. Co( ii ) and Ni( ii ) metallogels show nonlinear refractive indices ( n 2 I ) of (3.619 ± 0.146) × 10 −6 cm 2 GW −1 and (3.472 ± 0.102) × 10 −6 cm 2 GW −1 , respectively, and two photon absorption coefficients ( β ) of (1.503 ± 0.045) × 10 −1 cm GW −1 and (1.381 ± 0.029) × 10 −1 cm GW −1 at an excitation intensity of 140 GW cm −2 . We also studied the optical limiting properties with a limiting threshold of 9.57 mJ cm −2 . Therefore, both metallogels can be considered promising materials for photonic devices: for instance, for optical switching and optical limiting. Adipic acid-directed supramolecular self-healing Co( ii ) and Ni( ii )-metallogels have been achieved to explore a comparative study of third order optical non-linearity.