Induced Self-Assembly and Disassembly of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2′-yl)pyridine Complexes with Charge Reversal Properties: “Proof-of-Principle” Demonstration of Ratiometric Förster Resonance Energy Transfer Sensing of pH

A series of pH-responsive alkynylplatinum(II) 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) complexes with charge-reversal properties was synthesized, and the supramolecular assemblies between conjugated polyelectrolyte, PFP-OSO3–, and [Pt{bzimpy(TEG)2}{C≡C–C6H3−(COOH)2-3,5}]Cl (1) have been studied using UV–vis absorption, emission, and resonance light scattering (RLS) spectroscopy. An efficient Förster resonance energy transfer (FRET) from PFP-OSO3– donor to the aggregated 1 as acceptor with the aid of Pt(II)···Pt(II) interactions has been presented, which leads to a growth of triplet metal–metal-to-ligand charge transfer (3MMLCT) emission in the low-energy red region. The two-component PFP-OSO3––1 ensemble was then exploited as a “proof-of-principle” concept strategy for pH sensing by tracking the ratiometric emission changes. With the aid of judicious molecular design on the pH-driven charge-reversal property, the polyelectrolyte-induced self-assembly and the FRET from PFP-OSO3– to the platinum(II) aggregates have been modulated. Together with its excellent reversibility and photostability, the extra stability provided by the Pt(II)···Pt(II) and π–π stacking interactions on top of the electrostatic and hydrophobic interactions existing in polyelectrolye–complex assemblies has led to a selective and sensitive pH sensing assay.