Composed in the f-block: solution structure and function of kinetically inert lanthanide(iii) complexes

Abstract

It has been more than 15 years since the last authoritative report on the solution structure of lanthanide complexes made from cylcen derived polydentate ligands. The field has progressed and diversified, and tools have been developed that should enable a step-change in the field in the imminent future. This will only happen if the tools are used, and the results communicated in a form that is consistent within the field and readily accesible to scientists outside the field. In this perspective, the fundamental tools for designing and investigating kinetically inert lanthanide complexes in solution will be covered. The fundamentals of this type of complexes will be laid out. The conformations of lanthanide complexes from cyclen derived ligands and the rate of exchange between conformations will be linked to their H NMR and luminescence spectra. The information rich ligand- and metal centred emission spectra will be discussed, and the time-resolved luminescence decay lifetimes are shown to be directly related to the solution structure. The aim is to provide the reader with the information needed to become excited by lanthanide coordination chemistry.

π‐Expanded Thioxanthones – Engineering the Triplet Level of Thioxanthone Sensitizers for Lanthanide‐Based Luminescent Probes with Visible Excitation

“…A prerequisite for efficient sensitization of lanthanide(III) luminescence is that the chromophore and the lanthanide centre are in contact . As no coordinating atoms are present in the π‐extended thioxanthones, we must rely on a rigid ligand backbone to ensure that the antenna chromophore will collide with the lanthanide centre during the excited state lifetime.…”

“…This is also known as the antenna principle, where the sensitizer is considered a light harvesting antenna chromophore. Direct excitation of the Ln 3+ ions yields a low luminescence intensity due to their low molar absorption coefficients (ϵ≈0.1–1 M −1 cm −1 ) . While it is possible to do optical microscopy following direct excitation, bright lanthanide based probes must rely on sensitization via an antenna chromophore…”

“…Here, we chose to modulate the photophysical properties of thioxanthone by expanding the conjugated system of thioxanthone as illustrated in Scheme compounds 2 , 3 , and 9 . The target is absorption in the blue, a small singlet‐triplet splitting, and efficient population of first the triplet state and then the lanthanide(III) centre when the chromophore is incorporated in a kinetically inert lanthanide(III) complex …”

Luminescence from Lanthanide(III) Ions Bound to the Glycocalyx of Chinese Hamster Ovary Cells

“…The europium(III) emission spectraf rom the pixels containing europium(III) ions in Figure 2a re all similar. As the shapea nd relative peak ratios of the europium(III) spectrum depends on the symmetry and coordination chemistry, [1,14] it will be different when in solution comparedt owhen bound to the glycocalyx.To investigate the sharp lines resulting from lanthanide luminescencei nd etail, we chose to resolve these using our previously introduced image analysis method. [15] This allows the fluorescents ignal arising from lanthanide centered emissiont o be fully distinguished from auto-fluorescence and the signal arising from other fluorescentd yes.…”

“…The europium(III) emission spectraf rom the pixels containing europium(III) ions in Figure 2a re all similar. As the shapea nd relative peak ratios of the europium(III) spectrum depends on the symmetry and coordination chemistry, [1,14] it will be different when in solution comparedt owhen bound to the glycocalyx.…”