Influence of metal cations on the localization and nature of excited state in bimetallic heteroleptic complexes of ruthenium(ii)

The photophysical behavior of new type of bimetallic ruthenium complexes based on crown- and phenanthroline-containing ligands was evaluated. Ruthenium(ii) in the explored complexes was coordinated to the 1,10-phenanthroline moiety and caused a noticeable effect on the optical properties of the complex. The second cation was introduced into the macrocyclic cavity in such a way that its presence significantly enhances phosphorescence. It was demonstrated for the monoruthenium crown-containing complex bis(2,2-bipyridine-k4N1′,N1″)[2-(2-(2,3,5,6,8,9,11,12,14,15,16a,20a-dodecahydrobenzo[b][1,4,10,13,7,16]-tetraoxadithiacyclooctadecyn-18-yl)-1H-imidazo[4,5-f][1,10]phenanthroline-k2N7,N8]-ruthenium(ii) chloride that its exposure to visible light led to two different excitation pathways. Only one of them led to the excited state ³MLCT (metal-to-ligand charge transfer) responsible for its phosphorescence. The second excited state of ¹LLCT (ligand-to-ligand charge transfer) nature “withdraws” the excitation energy from the emitting state ³MLCT, thus reducing the quantum yield. The introduction of the second cation into the crown ether moiety significantly affected the electron density distribution; in particular, it hindered the transfer of electrons within the ligand common to the two cations. As a result, long-wave irradiation induced only the MLCT transition, which significantly increased the probability of radiative relaxation.