Polymers Composed of Alternating Anthracene and Pyridine Containing Units by Radical Ring-Opening Polymerization: Controlled Synthesis, Optical Properties, and Metal Complexes

Novel polymers composed of alternating anthracene and pyridine containing units were synthesized by radical ring-opening polymerization of pyridine-containing cyclic monomers via reversible addition-fragmentation chain transfer (RAFT) process. The ring-opening polymerization proceeded predominantly to afford well-defined polymers (M-w/M-n similar to 1.30), which exhibited the characteristic absorption and fluorescence due to the anthracene unit. On the other hand, fluorescence quenching was observed in chloroform and acidic aqueous solutions. The quenching was explained by charge transfer from the excited anthracene units to the coordinated or protonated pyridine units. Additionally, fluorescence quenching independent of external ambient conditions was conducted by quaternization. In the thin film state, the obtained polymers exhibited fluorescence due to the formation of excimers. The formation of complexes between the anthracene-containing polymers and metal species (Zn, Cu, and Co) led to the change in the optical properties compared to those of pristine polymers. These results demonstrate that the unique optical properties could be developed under various conditions due to the interactions between the anthracene and pyridine units in the well-defined polymers.