Controlled emission of platinum(II) terpyridyl complexes with poly-l-glutamic acid

Poly-l-glutamic acid, P(Glu), bearing multiple negatively charged side chains served as a polymeric spatially aligned scaffold for the aggregation of positively charged platinum(II) complexes [Pt(trpy)Ctriple bond; length of mdashCR](OTf) (trpy = 2,2′,6′,2″-terpyridine; R = Ph (PtH), PhC12H25-p (PtC12)) through electrostatic interaction, resulting in tunable emission properties. PtC12 was found to exhibit gradual increase in the emission intensity based on the triplet metal-metal-to-ligand charge transfer (3MMLCT) in a tris/HCl buffer (pH 7.6)/MeOH (v/v = 1/14) solution with concomitant decrease in the emission intensity based on the triplet metal-to-ligand charge transfer (3MLCT)/the triplet ligand-to-ligand charge transfer (3LLCT) as the amount of P(Glu) was increased. Such synergistic effect was not observed in the case of PtH, wherein the emission intensity based on 3MLCT/3LLCT was increased by the increase in the amount of P(Glu), indicating that alkyl long chain of PtC12 is considered to play an important role in the aggregation of the platinum(II) terpyridyl moieties to show Pt(II)–Pt(II) and π–π interactions.