Excited-states Dynamics Of Two Ir-Eu Bimetallic Complexes

There are plentiful energy levels for the f-f transition of the lanthanide ions, and the nature of their 4f shells results in some unique properties of the lanthanide, especially luminescence. Transition metal complexes are good candidates for antennae ligands due to their tunable d-transiton properties. d-f assemblies are good sources of strongly absorbing complexes extending the visible region, so this complexes are used in significant technological applications such as fluoroimmunoassay and cellular imaging. However, due to the intricate energy transfer processes leading to sensitization of lanthanide luminescence, in which broad-band and short-lived excited states from the ligands have to interact with narrow and long-lived metal-ion states, so the research of the excited states dynamics is significant.We have synthesized and characterized two Ir-Eu bimetallic complexes{[(dfppy)2Ir(μ-phen3f)]3EuCl}Cl2,{[(dfppy)2Ir(μ-phen5f)]3EuCl}Cl2. Results revealed that the minor alternation of the bridge ligand bring a tiny difference on the lowest triplet state energy and the EET efficiency from the Ir complex to the Eu ion, but a significant difference on the total luminescence quantum yields. Time resolved luminescence measurements and Global-fitting resolved energy transfer rates in the bi-metallic complexes, including the back energy transfer rate. The fitting results indicated that sensitization efficiencies of the two complexes are both high enough and the values are quite close. The non-radiation relaxation of the excited energy of the EuⅢion was used to explain the discrepancy of the quantum yields of the two complexes.