Purely heterometallic lanthanide (III) macrocycles through controlled assembly of disulfide bonds for dual color emission

Lanthanide complexes based on bis(amides) of diethylenetriaminepentaacetic acid with thiol functionalities are modified with 2,2′-dipyridyl disulfide to give activated complexes that can selectively react with thiol-functionalized complexes to form heterometallic lanthanide macrocycles. The preparation and full characterization of the polyaminocarboxylate ligands N,N′′-bis[p-thiophenyl(aminocarbonyl)]diethylenetriamine-N,N′,N′′-triacetic acid (H3Lx) and the activated N,N′′-bis[p-(pyridyldithio)[phenyl(aminocarbonyl)]]diethylenetriamine-N,N′,N′′-triacetic acid (H3Ly) and the complexes LaLx, NdLx, SmLx, EuLx, GdLx, DyLx, TbLx, ErLx, and YbLx are reported. The luminescence properties of the LnLx complexes emitting in the visible (where Ln = Dy3+, Tb3+, Eu3+, and Sm3+) are examined by steady-state and time-resolved photoluminescence, and the triplet state energy level of GdLx was estimated to be 24 100 cm−1 from the 0−0 band of the 77 K phosphorescence spectrum. Near-infrared emission was detected for the NdLx, YbLx, and ErLx complexes, demonstrating the versatility of the thiophenol chromophore. The assembly of purely heterometallic EuTbLx2 macrocycles by reaction of EuLx with TbLy was followed by UV−vis absorption spectroscopy, monitoring the characteristic absorption peak of pyridyl-2-thione at 353 nm. Analysis of the solution by mass spectrometry reveals the formation of purely heterometallic macrocycle EuTbLx2. This is in contrast with the results obtained by dynamic self-assembly under oxidative conditions, where we observe a statistical mixture of macrocyclic complexes of Eu2Lx2, Tb2Lx2, and EuTbLx2. The EuTbLx2 macrocycle displays dual color emission, incorporating the characteristic f−f transitions of Eu3+ and Tb3+. Investigation into the time-resolved photophysical properties of EuTbLx2 reveals energy transfer from Tb3+ to Eu3+, facilitated by the different conformations of the macrocycle in solution.