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

Authors

  • Dr. Csongor Szíjjártó,

    1. Department of Chemistry, BMC, Uppsala University, Box 576, 75123 Uppsala (Sweden), Fax: (+) 46-18-4714988
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    • These authors contributed equally to this work.

  • Elias Pershagen,

    1. Department of Chemistry, BMC, Uppsala University, Box 576, 75123 Uppsala (Sweden), Fax: (+) 46-18-4714988
    2. Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 10691, Stockholm (Sweden)
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    • These authors contributed equally to this work.

  • Nadia O. Ilchenko,

    1. Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 10691, Stockholm (Sweden)
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  • Dr.  K. Eszter Borbas

    Corresponding author
    1. Department of Chemistry, BMC, Uppsala University, Box 576, 75123 Uppsala (Sweden), Fax: (+) 46-18-4714988
    2. Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 10691, Stockholm (Sweden)
    • Department of Chemistry, BMC, Uppsala University, Box 576, 75123 Uppsala (Sweden), Fax: (+) 46-18-4714988
    Search for more papers by this author

Abstract

Coumarin-sensitized, long-wavelength-absorbing luminescent EuIII-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 H2O2 yielded the corresponding 7-hydroxycoumarin species. The same species was produced with peroxynitrite in a ×106–107-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 EuIII-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.

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