Phosphorescence quenching of a platinum acetylide polymer by transition metal ions

A platinum acetylide-based polymer (p-Pt2BPyPh) that contains 2,2′-bipyridine units in the polymer backbone has been synthesized. A model complex (Pt2BPyPh2) has also been prepared that features the same structure as a single polymer repeat unit. The polymer and model complex exhibit moderately efficient and long-lived phosphorescence emission from a triplet excited state. The effect of addition of six different transition metal ions (Fe3+, Co2+, Zn2+, Ni2+, Cu2+ and Pd2+) on the absorption and phosphorescence spectra of p-Pt2BPyPh and Pt2BPyPh was examined. The results show that in every case, the metal ions bind to the bipyridine unit in the polymer (model) backbone, and metal ion binding induces a red-shift in the near-UV absorption band. Phosphorescence spectroscopy shows that for all of the metals (with the exception of Zn2+), metal ion binding is accompanied by phosphorescence quenching. For some of the metal ions (Cu2+ and Ni2+) quenching of the polymer is considerably more efficient than in the model, an observation consistent with an “amplified quenching effect” that is analogous to that observed for quenching of fluorescent conjugated polymers. A semi-quantitative analysis of the absorption and phosphorescence data provide a model consistent with the notion that triplet exciton hopping along the polymer chain is rapid compared to the triplet lifetime, and that the overall quenching efficiency for the different metal ions is controlled by the intrinsic rate of triplet quenching within the metal ion–bipyridine complex.