Tris(2,2'-bipyridine)ruthenium(II) bis(hexafluorophosphate) is a coordination complex with the chemical formula [Ru(bpy)3](PF6)2. It is a red-orange crystalline solid that is soluble in polar organic solvents such as acetonitrile and dimethylformamide. This complex is one of the most extensively studied and prototypical metal polypyridyl complexes in photochemistry and electrochemistry. Its primary and most significant application is as a photosensitizer and an electron transfer mediator. It is a benchmark compound in dye-sensitized solar cells (DSSCs) due to its strong visible light absorption, long-lived excited state, and efficient electron injection into semiconductor oxides like TiO2. Beyond photovoltaics, it is widely used as a standard redox catalyst in photoredox catalysis for organic synthesis, enabling various C-C and C-heteroatom bond formations under mild conditions. It also serves as a luminescent probe and a standard in electrochemiluminescence (ECL) for analytical and bioanalytical applications. The complex exhibits excellent chemical stability and reversible redox behavior. Its excited state is a potent oxidant and reductant, making it a versatile tool in artificial photosynthesis and energy conversion research. Due to its central role in fundamental research, it is commercially available as a high-purity material from major chemical suppliers.