Transient near-IR absorption spectrum in laser flash photolyzed aqueous solutions of tris(2,2′-bipyridyl) ruthenium(II)

Laser flash photolysis of aqueous solutions of tris(2,2′-bipyridyl) ruthenium(II) cation (Ru(bpy)32+, bpy=2,2′-bipyridyl) induced transient absorbance changes in the near-IR region. The transient absorption with a peak at around 900 nm was assigned as a triplet–triplet transition of the metal-to-ligand charge transfer (MLCT) excited state of Ru(bpy)32+. The quantum efficiency for the MLCT state formation (φ) and the molar absorption coefficient at 900 nm (ϵ*) were determined to be φ=1.00±0.04 and ϵ*=1420±30 M−1 cm−1, respectively, by applying the method of intensity dependence measurement.