A Versatile Long‐Wavelength‐Absorbing Scaffold for Eu‐Based Responsive Probes

Abstract

Coumarin-sensitized, long-wavelength-absorbing luminescent Eu(III)-complexes have been synthesized and characterized. The lanthanide binding site consists of a cyclen-based chelating framework that is attached through a short linker to a 7-hydroxycoumarin, a 7-B(OH)(2)-coumarin, a 7-O-(4-pinacolatoboronbenzyl)-coumarin or a 7-O-(4-methoxybenzyl)-coumarin. The syntheses are straightforward, use readily available building blocks, and proceed through a small number of high-yielding steps. The sensitivity of coumarin photophysics to the 7-substituent enables modulation of the antenna-absorption properties, and thus the lanthanide excitation spectrum. Reactions of the boronate-based functionalities (cages) with H(2)O(2) yielded the corresponding 7-hydroxycoumarin species. The same species was produced with peroxynitrite in a ×10(6)-10(7)-fold faster reaction. Both reactions resulted in the emergence of a strong ≈407 nm excitation band, with concomitant decrease of the 366 nm band of the caged probe. In aqueous solution the methoxybenzyl caged Eu-complex was quenched by ONOO(-). We have shown that preliminary screening of simple coumarin-based antennae through UV/Vis absorption spectroscopy is possible as the changes in absorption profile translate with good fidelity to changes in Eu(III)-excitation profile in the fully elaborated complex. Taken together, our results show that the 7-hydroxycoumarin antenna is a viable scaffold for the construction of turn-on and ratiometric luminescent probes.

Lanthanide-Based Imaging of Protein–Protein Interactions in Live Cells

“…A number of Eu(III) complexes with appreciable absorptivity at ~400 nm have been developed using acridone, coumarin or azathiaxanthone as sensitizers. 76, 116–118 The previously mentioned pentadecanuclear Eu(III) clusters reported by Thielemann, et al also absorb in this wavelength range. 95 Recent work by Maury and co-workers shows that push-pull, aryl-alkynyl chromophores can sensitize Eu(III) emission from a charge transfer excited state, extending absorbance maxima well into the visible spectrum.…”

Responsive, Water‐Soluble Europium(III) Luminescent Probes

“…For instance, the use of benzylboronic acid as a protective group creates an H2O2--selective, non--ratiometric probe. However, a similar principle can yield ratiometric probes, as was demonstrated by the same group using [Eu.22] [38] . This time, the coumarin derivative bearing a chemoselective cleavable group (a boronic acid, in the case of H2O2 signalling) in a 7--position was pre--synthesised, and therefore the probe was already emissive before adding the analyte.…”

A novel DOTA-like building block with a picolinate arm for the synthesis of lanthanide complex-peptide conjugates with improved luminescence properties

“…The number of suitable antennas reported in the literature is rather limited [78][79][80] and acridone, which has been used in several DO3A-Eu 3+ complexes [46,[81][82][83], appeared to be the best choice. Additionally, 9-oxo-10(9H)acridineacetic acid, a carboxylate derivative, that can be readily coupled to a peptide, is commercially available.…”