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

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