Electronically exited states in triphenylphosphine complexes of Ruthenium (II): TD DFT study

Abstract Singlet and triplet electronically exited states (EES) of the luminescent and photoactive complexes [Ru(bpy) 2 (PPh 3 ) (L)] +2 , where bpy is 2,2′- bipyridyl, L is 4-aminopyridine, pyridine (py), or 4,4′- bipyridyl (bipy) are studied within TDDFT/B3LYP/[6‐31G(d) + LanL2DZ(Ru)] method in the energy region of 2.2 eV − 4.5 eV. We revealed the nature of more than 70 EES and constructed a series of multi-level schemes of the EE states, taking into account 3 dd levels of Ru (II) and metal-to-ligand charge-transfer states of pyridine ligands (MLCT(L)). These schemes gave us the opportunity to evaluate the activation energy of 3 dd-states of Ru (II) ion and to explain the weak luminescence of triphenylphosphine complexes of Ruthenium (II) (TPRC) at room temperature. Besides, we discovered that the emission energy (E em ) of the principal luminescent transition 3 MLCT  → 1 GS of the complexes studied depends linearly on the effective charge on the nitrogen atom (Q(N 4 )) of the coordinated pyridyl ligand. The electronic absorption spectra of TPRC are calculated and interpreted within TD DFT, and the energy of luminescent transition ( E T-S ) from the lowest triplet 3 MLCT to the ground state for all TPRC under study is evaluated. It is shown that the variation of pyridine ligands (L) from electron donors to electron acceptors results in the hypsochromic shift of E T-S , which is in good agreement with the experimental data.