Competing excitation paths in luminescent heterobimetallic Ln-Al complexes: Unraveling interactions via experimental and theoretical investigations

The interest for heterometallic lanthanide-d or-p metal (Ln-M) complexes is growing because of a potential cooperative or synergistic effect related to the proximity of two different metals in the same molecular architecture affording special tunable physical properties. To exploit the potentiality of Ln-M complexes, suitable synthetic approaches, and the in-depth understanding of the effect of each building block on their properties are mandatory. Here, we report the study on a family of heterometallic luminescent complexes [Ln(hfac)3Al(L)3], Ln= Eu3+ and Tb3+. Using different L ligands, we investigated the effect of the steric and electronic properties of the Al(L)3 fragment, highlighting the general validity of the employed synthetic route. A marked difference in the light emission of [Eu(hfac)3Al(L)3] and [Tb(hfac)3 Al(L)3] complexes has been observed. Thanks to photoluminescence experiments and Density Functional Theory calculations, Ln3+ emissions are explained with a model involving two non-interacting excitation paths through hfac or Al(L)3 ligands.