Design of ligands to obtain lanthanide ion complexes displaying high quantum efficiencies of luminescence using the sparkle model

摘要

In this paper we exemplify how to use our sparkle model for the calculation of lanthanide complexes (SMLC-AM1-INDO/SCI) together with Fermi's golden rule with the multipolar and exchange mechanisms to describe the ligand-lanthanide ion energy transfer for the purpose of designing ligands to obtain complexes displaying light quantum efficiencies of luminescence. Accordingly, we propose aromatic imides as efficient antennas and energy transfer ligands when coordinated to Eu~(3+) ion. More specifically we designed Eu(btfai)_3bipy (btfai = benzoyltrifluoroacetylimide anion and bipy = bipyridine) and Eu(bzaci)_3bipy (bzaci = benzoylacetylimide anion) which we then compare with their β-diketone analogues Eu(btfa)_3bipy (btfa = benzoyltrifluoroacetonate) and Eu(bzac)_3bipy (bzac = benzoylacetonate), which have been previously synthesized and whose quantum efficiencies we have also previously measured. Our theoretical results indicate that indeed the quantum efficiencies of Eu(btfai)_3bipy and Eu(bzaci)_3bipy are electronically equivalent to their highly luminescent β-diketone analogues with the advantage of one less hydrogen directly bonded to the central atom of the β-dicarbonylic anionic species. Indeed the possibility of vibronic coupling through that bond vibrational mode, which may be partially quenching the luminescence from the ~5D_0 level of the Eu~(3+) ion in the β-diketone analogues case, is thus eliminated.