Lanthanoid/Alkali Metal β-Triketonate Assemblies: A Robust Platform for Efficient NIR Emitters

The reaction of hydrated lanthanoid chlorides with tribenzoylmethane and an alkali metal hydroxide consistently resulted in the crystallization of neutral tetranuclear assemblies with the general formula fLn(Ae center dot HOEt)(L)(4)](2) (Ln = Eu3+, Yb3+; Ae=Na+, K+, Rb+). Analysis of the crystal structures of these species revealed a coordination geometry that varied from a slightly distorted square antiprism to a slightly distorted triangular dodecahedron, with the specific geometrical shape being dependent on the degree of lattice solvation and identity of the alkali metal. The near-infrared (NIR)-emitting assemblies of Yb3+ and Er3+ showed remarkably efficient emission, characterized by significantly longer excited state lifetimes (tau(obs) P -37-47 vs for Yb and is for Er3+) when compared with the broader family of lanthanoid p-diketonate species, even in the case of perfluorination of the ligands. The Eu3+ assemblies show bright red emission and a luminescence performance (tau(obs), approximate to ms, phi(L)(Ln)approximate to 35-37%, eta(sens) approximate to 68-70%) more akin to the (beta-diketonate species. The results highlight that the beta-triketonate ligand offers a tunable and facile system for the preparation of efficient NIR emitters without the need for more complicated perfluorination or deuteration synthetic strategies.