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 ³MLCT and ³LLCT structures and energies, we found that the ³MLCT 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 ³MLCT state and ³LLCT state, which gave a reasonable explanation for the luminescence properties of these complexes.