Lanthanide-based metallogels with tunable luminescence: nanomolar detection of a nerve agent simulant and anticounterfeiting applications†

This work presents two lanthanide-based metallogels, L1-Eu and L1-Tb, fabricated by coordination-driven self-assembly of an amide-based ligand containing a long alkyl chain (L1). The self-assembly of metallogels was investigated with the help of FTIR and NMR spectral, crystallographic, rheological, morphological, and molecular docking studies. These studies reveal a collective role of M–L coordination, π−π stacking, hydrogen bonding, and critical hydrophobic interactions amongst the alkyl chains in forming lanthanide-based metallogels. To evaluate the role of long alkyl chains in metallogel formation, several control molecules (L2–L4) were synthesized by varying the length of the attached alkyl chain. Notably, the alkyl chain length significantly impacted not only the metallogel formation but also their mechanical strength. Both L1-Eu and L1-Tb unveiled distinct and strong luminescent characteristics ascribed to lanthanide ions. The luminescence properties of metallogels were tuned by modulating the stoichiometry of lanthanide ions, and red, green, and near-white light-emitting metallogels were developed. Both metallogels were utilized for the selective and nanomolar detection of dimethyl methyl phosphonate (DMMP), a nerve agent simulant, and noteworthy anticounterfeiting applications.