Intercalation of Alkynylplatinum(II) Terpyridine Complexes into a Helical Poly(phenylene ethynylene) Sulfonate: Application to Protein Sensing

The interactions of two anionic poly­(phenylene ethynylene) sulfonate-conjugated polyelectrolytes (mPPESO3 and pPPESO3) with two alkynylplatinum­(II) terpyridine complexes (Pt2+ and Pt3+) were studied. The Pt­(II) complexes interact with helical mPPESO3 by intercalation within the polymer helix to form a “guest–host” ensemble. Titration of Pt­(II) complexes into an aqueous solution of mPPESO3 gives rise to efficient quenching of the polymer’s fluorescence; meanwhile, triplet metal–metal-to-ligand charge transfer (3MMLCT) state emission from the intercalated Pt­(II) complexes appears when the ensembles are excited into the polymer’s absorption band. The 3MMLCT state emission implies that the Pt­(II) complexes aggregate or dimerize on the mPPESO3 scaffold. The responses of the mPPESO3 and Pt­(II) complex ensembles to various proteins were examined by monitoring the mPPESO3 fluorescence change. Negatively charged proteins recover the mPPESO3 fluorescence more than the positively charged proteins under physiological pH, indicating that electrostatics play an important role in the protein–ensemble interaction.