A [Cyclentetrakis(methylene)]tetrakis[2‐hydroxybenzamide] Ligand That Complexes and Sensitizes Lanthanide(III) Ions

Abstract

The synthesis of the cyclen derivative H 4 L 1 ·2 HBr containing four 2-hydroxybenzamide groups is described. The spectroscopic properties of the Ln III conplexes of L 1 (Ln=Gd, Tb, Yb, and Eu) reveal changes of the UV/VIS-absorption, circular-dichroism-absorption, luminescence, and circularly polarized luminescence spectra. It is shown that at least two metal-complex species are present in solution, whose relative amounts are pH dependent. At pH > 8.0, an intense long-lived emission is observed (for [TbL 1 ] and [YbL 1 ]), while at pH < 8.0, a weaker, shorter-lived species predominates. Unconventional Ln III emitters (Pr, Nd, Sm, Dy, and Tm) were sensitized in basic solution, both in the VIS and in the near-IR, to measure the emission of these ions.

Structural and Photophysical Properties of Visible- and Near-IR-Emitting Tris Lanthanide(III) Complexes Formed with the Enantiomers of N,N′-Bis(1-phenylethyl)-2,6-pyridinedicarboxamide

“…27, 28, 38, 71, 72 On the other hand, one would have expected that the CPL would have been dependent on the excitation polarization if the solution would have contained a mixture of diastereoisomers. 73, 74 This is also in good agreement with the X–ray crystal structures of [Ln L 3 ] 3+ (Ln(III) = Eu, Gd, Tb, Yb and L = ( R , R )– 1 and ( S , S )– 1 ) showing the formation of triple helical complexes in the solid state (see below). In summary, the apparent easy formation of the 1:3 species contrasts with what was observed with L 8 , 58 and confirms that L is not blocked in the syn , syn , ZZ conformation.…”

“…It is worth mentioning that these observations are consistent with other published data. 74, 94, 95 As stated earlier, the nonradiative deactivation processes are amplified for Ln(III) ions with small energy gaps, and even more accentuated for NIR–emitting Ln(III)–complexes. 90, 92, 93, 96 However, the overall weak Ln(III)–centered NIR luminescence of [Ln L 3 ] 3+ is also due to the poor efficiency of the energy transfer processes within the ligand bands (ISC) and between the ligand and the Ln(III) ions.…”

Circularly Polarized Luminescence of Curium: A New Characterization of the 5f Actinide Complexes

“…In comparison to the lanthanides, these values for the Cm(III) complexes are not as large as the g lum values for [EuL1R/S] , previously reported with values of +0.298 and −0.294 (at an emission wavelength of 596 nm), 24 or with any other lanthanide complexes we have reported. 22–25 The g lum values for the CmL1R/S complexes were similar to the Tb(III) values determined with the same ligand L1R/S , (+0.044 and −0.048, respectively). It is important to note that although, Tb(III) and Cm(III) have some similarities with respect to excited state energies, it is unlikely that these similarities result in similar g lum , since other parameters (including coordination geometry and inner sphere solvent coordination as well as vibronic relaxations) play an influential role.…”

“…Circularly polarized luminescence and total luminescence spectra were recorded on an instrument described previously, 21–25 operating in a differential photon-counting mode. The light source for indirect excitation was a continuous wave 1000 W xenon arc lamp from a Spex FluoroLog-2 spectrofluorometer, equipped with excitation and emission monochromators with dispersions of 4 nm/mm (SPEX, 1681B).…”

“…Similar to CD, CPL can also discriminate between structurally similar luminescent chiral complexes/molecules. 21–25 In this work, octadentate chiral phenolate ligands, H(2,2)BnMe IAMS(−)/R(+) chiral ligands (both enantiomers denoted as L1 ), as well as a newly synthesized chiral cage, EtH(2,2)-BIAM ( L2 ), were used to form Cm(III) complexes (Scheme 1). 24, 26 The ligands L1 and L2 were selected based on the photophysical properties of the L1 terbium(III) complexes.…”