Shining light on the antenna chromophore in lanthanide based dyes

Abstract

Lanthanide based dyes and assays exploit the antenna effect, where a sensitiser-chromophore is used as a light harvesting antenna and subsequent excited state energy transfer populates the emitting lanthanide centred excited state. A rudimentary understanding of the design criteria for designing efficient dyes and assays based on the antenna effect is in place. By preparing kinetically inert lanthanide complexes based on the DO3A scaffold, we are able to study the excited state energy transfer from a 7-methoxy-coumarin antenna chromophore to europium(iii) and terbium(iii) centred excited states. By contrasting the photophysical properties of complexes of metal centres with and without accessible excited states, we are able to separate the contributions from the heavy atom effect, photoinduced electron transfer quenching, excited state energy transfer and molecular conformations. Furthermore, by studying the photophysical properties of the antenna chromophore, we can directly monitor the solution structure and are able to conclude that excited state energy transfer from the chromophore singlet state to the lanthanide centre does occur.

Investigating subtle 4f vs. 5f coordination differences using kinetically inert Eu(iii), Tb(iii), and Cm(iii) complexes of a coumarin-appended 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (DO3A) ligand

“…1 H and 13 C NMR spectra are included in the ESI Figures S1, S2, S4, and S5. The complexes presented in this report was prepared in situ, characterization of the isolated complexes can be found in reference 72. Synthesis 1-(7-methoxy-4-methyl-coumarin)-4-7-10--tris(tertbutoxycarbonylmethyl)-1,4,7,10-tetraazacyclododacane (1).…”

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

“…The synthesis of ligands H 3 L 1 and H 3 L 2 were performed following a two‐step synthetic route shown in Scheme . The tert ‐butyl triester of DO3A 12 was prepared as previously described, following the procedure developed by Sammes and Faulkner . Bromomethyl thioxanthone derivatives 10 or 11 was used to alkylate the secondary amine of the tert ‐butyl triester of DO3A 12 in MeCN at 60 °C with K 2 CO 3 .…”

“…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.…”

“…1,4,7‐tri( tert ‐butoxycarbonylmethyl)‐1,4,7,10‐tetraazacyclododecane, hydrobromide salt 12 . Cyclen (5.01 g, 29.08 mmol, 1 eq) was dissolved in acetonitrile (120 ml).…”

Combining the Best of Two Chelating Titans: A Hydroxypyridinone‐Decorated Macrocyclic Ligand for Efficient and Concomitant Complexation and Sensitized Luminescence of f‐Elements

“…These two decay rates indicate the presence of, at least, two different species in solution for the Eu(III) and Sm(III)-DOTHOPO systems. The aforementioned lifetimes are comparable to the time scale of arm rotation and ring inversion in lanthanidemacrocyclic complexes, [40] which prevented us from concluding whether these observations correspond to weighted average or reveal solution structure. In addition, a profound change in ligand field is required to discern any alteration in the luminescence properties, which might not be reached by simple structure fluctuation.…”