Impacts of terminal modification of [Ru(phen)₂dppz]²⁺on the luminescence properties: a theoretical study

Abstract

[Ru(phen)2dppz](2+) and other closely related ruthenium(II) complexes containing π-extended ligands were found to be non or weakly emissive in water, while exhibiting significant luminescence intensity growth when bound to DNA, however, a satisfactory interpretation has not been provided on this "light switch" mechanism. In the present study, we investigated the vertical transitions and triplet excited states of [Ru(phen)2dppz](2+) (1), [Ru(phen)2dppzi](2+) (2) and [Ru(phen)2dppz-idzo](2+) (3) in the gas phase and aqueous solution, through time dependent-density functional theory (TDDFT). Based on the optimized (3)MLCT and (3)LLCT structures and energies, we found that the (3)MLCT state might be responsible for the emissions of the complexes. Interesting connections between the singlet vertical transitions and the luminescence properties were noticed. Through ZORA-TDDFT calculation with perturbative SOC, we evaluated the intersystem crossing between the lowest singlet excited state, and both (3)MLCT state and (3)LLCT state, which gave a reasonable explanation for the luminescence properties of these complexes.

Direct observation by time-resolved infrared spectroscopy of the bright and the dark excited states of the [Ru(phen)2(dppz)]2+ light-switch compound in solution and when bound to DNA

“…A decrease in electron density on the Ru metal centre was also observed in both cases, which indicated that the triplet lowest excited states in both solvents have substantial metal-to-ligand charge-transfer character, with additional small contributions from a purely dppz ligand-centred transition. 19 – 22 …”

“… 5 , 31 While these studies clearly point to the presence of two distinct excited states, there has been some disagreement about the nature of these states in the literature, especially from computational studies. 19 – 22 …”

The role of substituted pyridine Schiff bases as ancillary ligands in the optical properties of a new series of fac-rhenium(i) tricarbonyl complexes: a theoretical view

“…3). 62,63 A similar calculation considering 40 excitations (with triplet state optimized) was used as the basis for the selfconsistent two-component spin-orbit coupling TDDFT (SOC-TDDFT) 64 within the ZORA Hamiltonian, where 6 spin-mixed excitations were calculated using the SR-TDDFT results as input. 27,65,66 Since the T 1 state is the lowest in the triplet manifold, the T 1 geometry can be optimized like a regular ground state.…”

“…3). 62,63 Usually, the triplet state is lower in symmetry than the ground state; thus, it is not recommended to consider symmetry restrictions. In this part of the work, we are interested in electronic transitions between the visible and ultraviolet regions.…”

Prolonged Luminescence Lifetime of a Dual Emissive Ruthenium Dipyridophenazine-Type Complex in Aprotic and Protic Solvents

“…Thus, for Ru­(II) dppz complexes, the luminescence is switched off in protic solvents . Several modifications on the dppz ligand were introduced in the past three decades, and their effect on the photophysical properties were investigated thoroughly. − Importantly, related oligopyridophenazines strongly related to the dppz core play an important role in artificial photosynthesis and directional photoinduced electron-transfer reactions. , …”