Abstract
We present a combined experimental and computational density functional theory (DFT)/time-dependent DFT study of the geometry, electronic structure and optical absorption spectrum of the solar-cell sensitizers
cis-[Ru(4,4′-COO
−-2,2′-bpy)
2(X)
2]
4− (X
=
NCS, Cl) in water solution. The experimentally observed red-shift of the spectrum upon substitution of NCS-by Cl-is well reproduced by our theoretical model and appears to be related to stabilization of the t
2g–π
∗ HOMOs in the NCS
− complex. The π
∗ LUMOs of the Cl complex are destabilized by a smaller extent with respect to the HOMOs, due to the increased π-back bonding interactions with the bipyridine ligands.