terpyridine

Terpyridine, or 2,2':6',2''-terpyridine, is a heteroaromatic compound that consists of three connected pyridine rings forming a rigid, planar tridentate nitrogen donor ligand. In the common 2,2':6',2''-terpyridine arrangement, the rings share two carbon bridges at the 2- and 2''-positions. The molecule has the empirical formula C15H11N3 and is a precursor to many metal–terpyridine complexes.

Terpyridine acts as a tridentate ligand, binding a metal center through its three pyridine nitrogens to form chelate rings. This binding confers high stability to many transition-metal complexes and often imparts interesting photophysical and redox properties, including metal-to-ligand charge transfer (MLCT) transitions. Substitution on the terpyridine rings can tune electronics, solubility, and coordination behavior. Various synthetic routes exist, often employing Kröhnke-type reactions or condensation methods to assemble the three pyridine rings into the terpyridine framework.

Applications of terpyridine and its metal complexes span coordination chemistry, catalysis, and materials science. Ruthenium(II) and iron(II) terpyridine complexes are particularly well known for their luminescence and light-absorption properties, making them important in dye-sensitized solar cells, light-emitting devices, and photocatalytic systems. Terpyridine ligands are also widely used in supramolecular chemistry and in the construction of coordination polymers and metal–organic frameworks.