The quenching of sensitized Eu­(III) luminescence by photoinduced electron transfer from the excited light-harvesting antenna to Eu­(III) was investigated. A series of complexes incorporating different metal binding sites and thus having varying Eu­(III)/Eu­(II) reduction potentials were prepared. The complexes were fully characterized using a combination of single-crystal X-ray crystallography and paramagnetic 1H NMR spectroscopy, the results of which support the structural similarity of the complexes. The redox and photophysical behavior of the Eu­(III) center and the light-harvesting antenna were studied using cyclic voltammetry and steady-state and time-resolved emission spectroscopy on the nanosecond and millisecond time scales. The contribution of photoinduced electron transfer to the overall reduction of the Eu­(III) luminescence quantum yield was found to be comparable and, in many cases, larger than the quenching caused by well-established processes such as coupling to X–H oscillators. These results suggest that the elimination or mitigation of photoinduced electron transfer could substantially improve the emissive properties of the widely used Eu­(III)-based emitters.

A series of luminescent lanthanide(iii) complexes consisting of 1,4,7-triazacyclononane-1,4-picolinate frameworks and three secondary amidelinked carbostyril antennae were synthesised and characterised.

Azide-and alkyne-functionalized bioconjugable luminescent lanthanide complexes are reported. Reactive handles were introduced into the complexes by the late-stage modification of a methylenecarboxylic acid antenna pendent group. Tb and Eu quantum yields (11−13% and 3.4−3.6%, respectively) were not greatly affected by the presence of the azide or the alkyne compared to the parent complex (Φ Tb = 10%, Φ Eu = 2.8%). Two avenues were explored for improving the luminescence of the lanthanide (Ln) complexes: (1) attaching the antenna through a tertiary amide linker and (2) replacing a monodentate carboxylate ligand with a bidentate pyridylcarboxylate donor, which yielded a nonadentate ligand that could saturate the lanthanide coordination sphere and eliminate the quenching metal-bound water molecule that was present in the octadentate complexes. The combination of both approaches yielded Eu and Tb emitters with 5.8% and 46% quantum yields. For the Eu complex, this value was the same as Φ Eu in the octadentate parent complex. We attribute this to increased photoinduced electron transfer quenching in the nonadentate species, which compensates for the reduced O−H quenching.