Supramolecular Frameworks from Graphene Edge-Grafted with Ni-Salphen Complexes and Pd-PTA Linkers

Edge oxidized graphene oxide (EOGO) is a promising graphene variant that has remained broadly unexplored as a two-dimensional (2D) supramolecular building block. This work aimed to construct graphene supramolecular frameworks (GSFs) using EOGO building blocks and [PdCl₂(3,5,7-triaza-7-phosphaadamantane)₂] (Pd-PTA) as ditopic guest linkers through noncovalent reticulation. Pd-PTA facilitated host-guest-host interconnection of the graphene units selectively through supramolecular hinges based on a Ni-Salphen scaffold hydroxylated at variable positions but formerly grafted to the carboxyl moieties exclusively present at the EOGO edges to maximize directional efficiency in reticulation. Synthesis and characterization of the supramolecular complexes formed between the Ni-Salphen variants and Pd-PTA, together with spectrophotometric titrations in solution, have confirmed concurrence of 1:1 and 2:1 stoichiometries for the [Ni-Salphen]/[Pd-PTA] systems. In contrast, EOGO-g-[Ni-Salphen] hybrid counterparts developed stoichiometry 1:1 for [Ni]/[Pd-PTA] at up to 1000-fold higher K ₁₁ and depicted the emergence of successive host-guest-host concatenation at [Ni] via 1:2 species formed through similar strength (K ₁₁∼K ₁₂). This stoichiometric inversion apparently enabled a cooperative oligomerization, as was further suggested by Hill plots and a concentration-dependent rise in fluorescence that progressed asymptotically upon the addition of Pd-PTA. Kinetically controlled assembly and solvent evaporation facilitated long-range arrangements, which we confirmed qualitatively and quantitatively by solid-state evaluations, thus offering a next generation of supramolecular frameworks.