Luminescent lanthanide (Ln(III)) complexes with coumarin or carbostyril antennae were synthesized and their photophysical properties evaluated using steady-state and time-resolved UV-vis spectroscopy. Ligands bearing distant hydroxycoumarin-derived antennae attached through triazole linkers were modest sensitizers for Eu(III) and Tb(III), whereas ligands with 7-amidocarbostyrils directly linked to the coordination site could reach good quantum yields for multiple Ln(III), including the visible emitters Sm(III) and Dy(III), and the near-infrared emitters Nd(III) and Yb(III). The highest lanthanide-centered luminescence quantum yields were 35% (Tb), 7.9% (Eu), 0.67% (Dy), and 0.18% (Sm). Antennae providing similar luminescence intensities with 2-4 Ln-emitters were identified. Photoredox quenching of the carbostyril antenna excited states was observed for all Eu(III)-complexes and should be sensitizing in the case of Yb(III); the scope of the process extends to Ln(III) for which it has not been seen previously, specifically Dy(III) and Sm(III). The proposed process is supported by photophysical and electrochemical data. A FRET-type mechanism was identified in architectures with both distant and close antennae for all of the Lns. This mechanism seems to be the only sensitizing one at long distance and probably contributes to the sensitization at shorter distances along with the triplet pathway. The complexes were nontoxic to either bacterial or mammalian cells. Complexes of an ester-functionalized ligand were taken up by bacteria in a concentration-dependent manner. Our results suggest that the effects of FRET and photoredox quenching should be taken into consideration when designing luminescent Ln complexes. These results also establish these Ln(III)-complexes for multiplex detection beyond the available two-color systems.

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.

Carbostyrils are among the most widely used sensitising antennae for luminescent lanthanides; they afford bright complexes with Eu and Tb, and can also sensitise the emissions of the less commonly used Sm, Dy, Yb and Nd. Systematic studies on the effect of structural variations on the photophysical properties and lanthanide sensitising abilities of carbostyrils can therefore have a large impact. We replaced the secondary amide linker that connects the metal binding site to the antenna with a carboxymethylsubstituted tertiary amide. Eight Tb and Eu complexes were prepared. All had higher lanthanide luminescence quantum yields (Φ Ln ) than their secondary amide analogues; three Tb emitters had Φ Tb > 40%. Eu complexes had Φ Eu up to 11.6%. The antenna singlet and triplet excited states are slightly shifted, while the metal coordination sphere is unchanged by the introduction of the carboxymethyl group.

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.

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Controlled, photocatalytic C−H bond activations are key reactions in the toolkits of the modern synthetic chemist. While it is known that the uranyl(VI) ion, [UVIO2]2+, the environmentally dominant form of uranium, is photoactive, most literature examines its luminescent properties, neglecting its potential synthetic utility for photocatalytic C−H bond cleavage. Here, we synthesise and fully characterise an air‐stable and hydrocarbon‐soluble uranyl phenanthroline complex, [UVIO2(NO3)2(Ph2phen)], UPh2phen, and demonstrate that it can catalytically abstract hydrogen atoms from a variety of organic substrates under visible light irradiation. We show that the commercially available parent complex, uranyl nitrate ([UVIO2(NO3)2(OH2)2]⋅4H2O; UNO3), is also competent, but from electronic spectroscopy we attribute the higher rates and selectivity of UPh2phen to ligand‐mediated electronic effects. Ketones are selectively formed over other oxygenated products (alcohols, etc.), and the catalytic oxidation of substrates containing a benzylic C−H position is particularly improved for UPh2phen. We also show uranyl‐mediated photocatalytic C−C bond cleavage in a model lignin compound for the first time.

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.

The coordination compounds of the trivalent lanthanide ions (Ln(III)) have unique photophysical properties. Ln(III) excitation is usually performed through a light-harvesting antenna. To enable Ln(III)-based emitters to reach their full potential, an understanding of how complex structure affects sensitization and quenching processes is necessary. Here, the role of the linker between the antenna and the metal binding fragment was studied. Four macrocyclic ligands carrying coumarin 2 or 4-methoxymethylcarbostyril sensitizing antennae linked to an octadentate macrocyclic ligand binding site were synthesized. Complexation with Ln(III) (Ln = La, Sm, Eu, Gd, Tb, Yb and Lu) yielded species with overall −1, 0, or +2 and +3-charge. Paramagnetic 1H NMR spectroscopy indicated subtle differences between the coumarin- and carbostyril-carrying Eu(III) and Yb(III) complexes. Cyclic voltammetry showed that the effect of the linker on the Eu(III)/Eu(II) apparent reduction potential was dependent on the electronic properties of the N-substituent. The Eu(III), Tb(III) and Sm(III) complexes were all luminescent. Coumarin-sensitized complexes were poorly emissive; photoinduced electron transfer was not a major quenching pathway in these species. These results show that seemingly similar emitters can undergo very different photophysical processes, and highlight the crucial role the linker can play.