Luminescent sensing and formation of mixed f–d metal ion complexes between a Eu(iii)-cyclen-phen conjugate and Cu(ii), Fe(ii), and Co(ii) in buffered aqueous solution

Abstract

The synthesis and photophysical properties of the Eu(III) complex 1.Eu, based on the use of 1,10-phenanthroline (phen) as a combined sensitizing antenna and a transition metal ion coordinating ligand, is described. The long-wavelength Eu(III) emission from this complex was found to be highly pH sensitive, giving rise to a 'off -on-off ' pH profile with maximum emission occurring within the physiological pH range. This allowed for the use of 1.Eu as a luminescent sensor for transition metal ions, where the titration with ions such as Cu(II), Co(II) and Fe(II) gave rise to the formation of mixed f -d nuclear complexes, with concomitant changes in the photophysical properties of 1.Eu. Here, changes in both the ground and the singlet excited state properties of the phen antenna were observed, but the largest changes were observed for the delayed Eu emission, which was fully quenched upon titration with these ions in aqueous pH 7.4 buffered solutions. In comparison, no changes were observed in the Eu(III) emission upon titration with ions such as Zn(II) or group I and II ions. From these changes, we were able to demonstrate the binding stoichiometry and the binding constant for the formation of novel supramolecular complexes between 1.Eu and Cu(II), Co(II) and Fe(II), which showed that either two or three equivalents of 1.Eu complexed to each of these transition metal ions, giving rise to the formation either linear f -d-f or branched f 3 -d based mixed nuclear complexes in solution.

The btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] binding motif: a new versatile terdentate ligand for supramolecular and coordination chemistry

“…19,20 Earlier this year, we demonstrated the potential of dpa as a central core for the generation of [2]-and appendant arm on cyclen (1,4,7,10-tetraazacyclododecane) complexed Ln(III) structures (we also employed this f-d metal ion hybrid strategy for the recognition of nucleic acids). 56,58 So how well does the btp ligand compare to these classical examples listed above? Flood et al pointed out, when first investigating the btp motif, that btp 0 (containing 1,2,4-triazoles) had been extensively studied as a coordination ligand.…”

Lanthanide luminescence sensing of copper and mercury ions using an iminodiacetate-based Tb(III)-cyclen chemosensor

“…[5][6][7] The unique photophysical properties of the lanthanides, [8][9][10] such as long wavelength emissions, sharp line-like bands and relatively long-lived excited state lifetimes [µs for Yb(III) and Nd(III) to ms for Eu(III) and Tb(III)], makes them very attractive candidates for such application in in vivo sensing as well as for biological imaging, another topical area of research. 5,[10][11][12] Careful functionalisation of the macrocyclic framework, 1,4,7,10-tetraazacyclododecane (cyclen) has allowed for the formation of many examples of thermodynamically stable and kinetically inert complexes with Ln III ions, which have been employed in luminescent sensing of metal ions. [12][13][14][15][16][17] These possess a suitable antennae/receptor unit which can populate the lanthanide excited states via an energy sensitization process (e.g.…”

“…5,[10][11][12] Careful functionalisation of the macrocyclic framework, 1,4,7,10-tetraazacyclododecane (cyclen) has allowed for the formation of many examples of thermodynamically stable and kinetically inert complexes with Ln III ions, which have been employed in luminescent sensing of metal ions. [12][13][14][15][16][17] These possess a suitable antennae/receptor unit which can populate the lanthanide excited states via an energy sensitization process (e.g. the antenna effect); which are perturbed upon binding to ions, giving rise to changes in both the lanthanide emission intensities and lifetimes.…”

Hierarchical Self‐Assembly of Luminescent EuIII Complexes on Silicon

“…The exact mass values were determined using a LTQ ORBITRAP XL Thermo spectrometer equipped with an electrospray interface. This section only includes the synthesis and characterization of ligand 1 from commercially available 5-amino-1,10-phenanthroline (5), through a modified literature procedure [14] and self-assembly in solution and on a silicon surface; syntheses of tetraphosphonate cavitands Tiiii-A [23] and Tiiii-B without the methyl groups at the upper rim. [24] The NMR and MS spectra of the formation of complexes can be found in the Supporting Information.…”

“…Accordingly, materials based on Eu III and Tb III are extensively utilized in light-conversion molecular devices, as phosphors in lighting technologies, as well as for sensing purposes and memory devices. [13,14] Although some examples of Eu III complexes covalently attached on surfaces have been reported, [15,16] to the best of our knowledge no examples of noncovalent self-assembly of lanthanide luminescent probes on silicon surfaces have been described in the literature.…”