Spectroscopic study on the 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine and its metal complexes

Multitopic ligand, 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine (pyterpy), has attracted growing attention because of its unique structural features, optical and electrochemical properties. Here, we report spectroscopic studies of pyterpy and its metal complexes in methanol solution. For the pure pyterpy, the ligand emission intensity increased with its concentration in the dilute solution, but decreased when its concentration was over 1.3×10⁻⁵ mol/l due to the concentration quenching. No significant influence on the ligand luminescence was observed for the Zn²⁺-pyterpy complex but strong luminescence quenching was observed for the electroactive Fe²⁺- and Co²⁺-pyterpy complexes. The lanthanide (Sm³⁺, Eu³⁺ and Tb³⁺) complexes of the pyterpy showed both ligand and lanthanide ion emissions, especially for the Tb³⁺-pyterpy complex, suggesting that the excited energy of pyterpy ligand could be efficiently transferred to the central Tb³⁺ ions. The luminescence was pH sensitive with the strongest emission in the neutral solution. The results indicated that the multitopic ligand of pyterpy could not only act as linkers for the metal-directed building blocks, but also act as optical materials with its own emission at about 364 nm and as light antenna for the lanthanide ions.