New Photosensitizers of the Ruthenium‐Polypyridine Family for the Water Splitting Reaction

The photophysical and electron transfer properties of the following Ru(II) complexes have been characterized: Ru(bpy)3‐n (biq)2+n, Ru(bpy)2(Cl2‐bpy)2+, Ru(Cl2‐bpy)2+3, Ru(bpy)2(NO2‐bpy)2+, Ru(NO2‐bpy)2+3, Ru(bpy)2(opdi)2+, Ru(bpy)2(phedi)2+, where n = 1 to 3, bpy = 2,2′‐bipyridine, biq = 2,2′‐biquinoline, and opdi and phedi are o‐quinodiimine ligands. The properties of these and other Ru‐polypyridine type photosensitizers are discussed on the basis of the requirements needed to split water with solar energy in an efficient way. It is shown that the Ru(bpy)2(LL)2+ complexes, where LL is a polypyridine‐type ligand which is easier to reduce than bpy, are expected to be more efficient photosensitizers than Ru(bpy)2+3.