Ligand Influence on the Electronic Spectra of Dicationic Ruthenium-Bipyridine-Terpyridine Complexes

We report electronic spectra of a series of ruthenium polypyridine complexes of the form [(trpy)­(bipy)Ru^II–L]²⁺ (bipy = 2,2′-bipyridine and trpy = 2,2′:6′,2″-terpyridine), where L represents a small molecular ligand that occupies the last coordination site. Species with L = H₂O, CO₂, CH₃CN, and N₂ were investigated in vacuo using photodissociation spectroscopy. All species exhibit bright metal-to-ligand charger transfer (MLCT) bands in the visible and near UV, but with different spectral envelopes and peak energies, encoding the influence of the ligand L on the electronic structure of the complex. Several individual electronic bands can be resolved for L = H₂O and CO₂, while the spectra for L = N₂ and CH₃CN are more congested, even at low ion temperatures. The experimental results are discussed in the framework of time-dependent density functional theory.