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 ( m PPESO 3 – and p PPESO 3 – ) with two alkynylplatinum(II) terpyridine complexes (Pt 2+ and Pt 3+ ) were studied. The Pt(II) complexes interact with helical m PPESO 3 – by intercalation within the polymer helix to form a “guest–host” ensemble. Titration of Pt(II) complexes into an aqueous solution of m PPESO 3 – gives rise to efficient quenching of the polymer’s fluorescence; meanwhile, triplet metal–metal-to-ligand charge transfer ( 3 MMLCT) state emission from the intercalated Pt(II) complexes appears when the ensembles are excited into the polymer’s absorption band. The 3 MMLCT state emission implies that the Pt(II) complexes aggregate or dimerize on the m PPESO 3 – scaffold. The responses of the m PPESO 3 – and Pt(II) complex ensembles to various proteins were examined by monitoring the m PPESO 3 – fluorescence change. Negatively charged proteins recover the m PPESO 3 – fluorescence more than the positively charged proteins under physiological pH, indicating that electrostatics play an important role in the protein–ensemble interaction.