Pt(II) Complex-Based Supramolecular Polymers with Fe(II) Ion

Abstract

In recent years, there has been significant interest in supramolecular architectures such as helical fibers, tubules, and nanotoroids (nanorings) due to their unique physical properties. In this study, we synthesized bis[terpyridine-based Pt(II)] complexes with an unoccupied terpyridine moiety on the opposite side. Interestingly, the mononuclear terpyridine-based Pt(II) complexes (Pt-L¹ and Pt-L²) form helical supramolecular polymers. These supramolecular polymers, exhibited intense photoluminescence at 570–620 nm, corresponding to metal-to-ligand charge transfer (MLCT) and/or metal-metal ligand charge transfer (MMLCT). Conversely, the supramolecular polymers formed in the presence of Fe²⁺ ions were non-emissive. The metallosupramolecular polymers formed in the absence and presence of Fe²⁺ ions were generated by π-π and intermolecular hydrogen bonding interactions and/or Pt⋅⋅⋅Pt interactions. The supramolecular polymers were formed through a cooperative pathway involving a nucleation-elongation mechanism. The nonsigmoidal transition of the absorbance change could be fitted by using the equilibrium (EQ) model, from which the thermodynamic parameters (ΔG_e, ΔH_e, and ΔS) were determined. At 4 mM, the Gibbs′ free energy (ΔG_e) of the supramolecular polymers of Pt-L¹ and Pt-L² without metal ions was calculated to be −18.9 and −17.4 kJ/mol, respectively.