The role of 4,7-disubstituted phenanthrolineligands in energy transfer of europium(iii) complexes: a DFT study

Abstract

Density functional theory/time-dependent density functional theory (DFT/TD-DFT) calculations were performed on a series of europium(III) complexes of 4,7-disubstituted-1,10-phenanthroline ligands (phen-X) of general formula Eu(TTA)₃(phen-X) (where TTA stands for thenoyltrifluoroacetonato and X = H, CH₃, OCH₃, Cl, Br, CO₂Et, C₆H₅, C₄HOCH₃ and C₄H₃OCH₃). The effect of such substitution on the structural, electronic and photophysical properties is established. Absorption spectra calculations show that different phen substituents have different effects on absorption peak positions and on transition characters while only substituent's influence via extended π-conjugation of the phen ligand can effectively tune the triplet state. Considering the ΔE_ISC and ΔE_ET values, the luminescent ⁵D₀ state of the Eu³⁺ ion can be efficiently populated in most complexes. The exceptions are the complexes with CO₂Et and C₄H₃OCH₃ groups.