Theoretical modelling of the low quantum yield observed in an Eu(III) triple helical complex with a tridentate aromatic ligand

Abstract

The dramatic decrease in the quantum yield of the Eu-centred luminescence recently observed in going from [Eu(NO₃)₃L(MeOH)] (2.8%) to the triple helical [Eu(L)₃](ClO₄)₃ complex (8.2 × 10⁻⁵%) prompted us to perform a theoretical analysis in order to find out which parameter might be responsible for this quenching. In particular, we explore the influence of a resonance between a ligand-to-metal charge-transfer state (LMCT) and the ¹ππ* and/or ³ππ* states on the emission quantum yield. A good agreement between the theoretical and experimental values is reached when high rates for non-radiative deactivation on the ligand are considered and, for the 1: 3 complex, when a LMCT state close in energy to the ligand ¹ππ* state is taken into account. This type of modelling opens the way for a better predictability of the photophysical properties of luminescent europium-containing edifices.