New Lanthanide Complexes for Sensitized Visible and Near-IR Light Emission:  Synthesis, ¹H NMR, and X-ray Structural Investigation and Photophysical Properties

Abstract

We describe the syntheses, the 1H NMR studies in CD3OD and D2O as solvent, the X-ray characterization, and the luminescence properties in D2O solution of the two complexes Eu.1 and Er.1, where 1 is a dipartite ligand that includes (i) a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) unit serving as hosting site for the metal center; and (ii) a phenanthroline unit which plays the role of light antenna for the sensitization process of the metal centered luminescence. In a previous report (Inorg. Chem. 2002, 41, 2777), we have shown that for Eu.1 there are no water molecules within the first coordination sphere. X-ray and 1H NMR results reported here are consistent with full saturation of the nine coordination sites within the Eu.1 and Er.1 complexes. In addition, these studies provide important details regarding the conformations, square antiprism (SAP) and twisted square antiprism (TSAP), adopted in solution by these complexes. The luminescence results are consistent with both an effective intersystem crossing (ISC) at the light absorbing phenanthroline unit (lambda(exc) = 278 nm) and an effective energy transfer (en) process from the phenanthroline donor to the cation acceptor (with unit or close to unit efficiency for both steps). In D2O solvent, the overall sensitization efficiency, phi(se), is 0.3 and 5 x 10(-6), for Eu.1 (main luminescence peaks at 585, 612, 699 nm) and Er.1 (luminescence peak at 1530 nm), respectively. The photophysical properties of both complexes are discussed with reference to their structural features as elucidated by the obtained 1H NMR and X-ray results.

Synthesis and Photoluminescence Properties of Heteroleptic Europium(III) Complexes with Appended Carbazole Units

“…[30,31] For Eu III and lanthanide complexes in general, the intramolecular energy migration efficiency from the chelating and/or appended ligands to the central Ln 3+ ion is the most important step influencing their luminescence output. [30] The intersystem-crossing efficiency and the intrinsic luminescence quantum yield of the Ln III ion are the other steps regulating the overall efficiency of Ln III -sensitized emission.…”

Syntheses, Structures and Photophysical Properties of New Heterodinuclear Cd–Ln Coordination Complexes (Ln = Sm, Eu, Tb, Nd, Ho, Er)

“…= 345 nm, complex 1 exhibits a broad and strong emission band at 360-500 nm, which should be assigned to a ligand-to-metal charge transfer (LMCT) of the d block (Cd-L section), [29,30] because the emission band is different from that of the free ligands (4-methoxybenzoic acid and phen) in shape and position; moreover, the emissions of the ligands have been quenched. In the emission spectrum of complex 1 (Figure 5), the other three peaks at 562, 598 and 644 nm are weaker and correspond to 4 [14,31] which indicates that the energy transfer from the d block to the f block is incomplete and most of the energy is used for luminescence from the d block itself. In the emission spectra of complexes 2 and 3 ( Figures 6 and 7 [28,32] The intensity of the 5 D 0 Ǟ 7 F 2 transition (electric dipole) is stronger than that of the 5 D 0 Ǟ 7 F 1 transition (magnetic dipole), and this indicates that the coordination environment of the Eu III ion is asymmetric, which is confirmed by the crystallographic analysis.…”

“…In addition, the emission properties of this family of complexes are notable, and the emissions cover an exceptionally wide spectral range: near-infrared (Nd III . [4] Recently, much attention has been paid to the luminescence properties of lanthanide complexes in the near-infrared region. Lanthanide complexes that emit in the NIR region, a region where biological tissues and fluids are relatively transparent, have the potential for use in chemosensor and fluoroimmunoassay applications as well as optical amplification in lasers.…”

NIR fluorescent ytterbium compound for in vivo fluorescence molecular imaging

“…Eu, Tb, Nd, Yb, and Er) complexes that include an antenna moiety, a sensitizing chromophore, are well known as good fluorophores. [5][6][7][8] Their useful emission features, such as a large Stoke's shift (over 10 times larger than typical fluorescent dyes) and element-specific emission wavelength (visible in the IR region), have the potential for fluorescence imaging. Nd and Yb ions are especially suited for in vivo fluorescence imaging because of their NIR luminescence originating from 4 F 3/2 to 4 I 9/2 (at 870 nm) and 2 F 5/2 to 2 F 7/2 (at 975 nm) transitions, respectively.…”

“…This implies that the complex would not be susceptible to metabolic degradation in living systems. [6] As an antenna moiety, (E )-1-(pyridin-2-yl-diazenyl)naphthalen-2-ol (PAN) was selected for three reasons. First, it is well known that PAN absorbs blue-green light (around 500 nm), which is harmless to living systems and reasonable for Yb excitation.…”