Lanthanide complexes photophysical properties

Chauvin, A.S., Gumy, R, Matsubayashi, I., etal. (2006) Fluorinated fl-diketones for the extraction of lanthanide ions photophysical properties and hydration numbers of their Eu " complexes. European Journal of Inorganic... 

LANTHANIDE COMPLEXES AS PROBES BASIC PHOTOPHYSICAL PROPERTIES 917... 

Photophysical studies have been conducted on a number of lanthanide complexes of calix[n]arenes, and a significant number of these are discussed in a recent review (79). The first europium and terbium calixarene complexes showed promising photophysical properties, with terbium luminescence lifetime of 1.5 ms and quantum yield of 0.20 in aqueous solution (80). 

Complexes of calixarenes with bipyridyl chromophores can be stabilized by the addition of anionic side arms, such as iminodiacetate units (85). Whilst the lanthanide complexes of ligands [L51]4- and [L52]4- are not soluble in water, their photophysical properties in... 

The first cage lanthanide complexes studied for their photophysics were the simple 2.2.1 cryptands. The lack of a strongly absorbing chromophore, and easy approach of solvent molecules meant that their luminescence properties were disappointing in comparison to many recently studied complexes. The Lehn cryptand (L53) (Scheme 6... 

Mono- and bimetallic lanthanide complexes of the tren-based macrobicyclic Schiff base ligand [L58]3- have been synthesized and structurally characterized (Fig. 15), and their photophysical properties studied (90,91). The bimetallic cryptates only form with the lanthanides from gadolinium to lutetium due to the lanthanide contraction. The triplet energy of the ligand (ca. 16,500 cm-1) is too low to populate the terbium excited state. The aqueous lifetime of the emission from the europium complex is less than 0.5 ms, due in part to the coordination of a solvent molecule in solution. A recent development is the study of d-f heterobimetallic complexes of this ligand (92) the Zn-Ln complexes show improved photophysical properties over the homobinuclear and mononuclear complexes, although only data in acetonitrile have been reported to date. 

Piguet, C. Biinzli, J.-C. G. Bernardinelli, G. Hopfgartner, G. Williams, A. F. Self-assembly and photophysical properties of lanthanide dinuclear triple-helical complexes. J. Am. Chem. Soc. 1993,115, 8197-8206. 

Although structurally and spectrally similar, the differing redox and photophysical properties of the various lanthanide(III) texaphyrin complexes allow their use in such disparate areas as PDT, direct cancer treatment, and both X-ray and chemotherapy enhancement protocols. Both compounds 1 and 2 generate reactive oxygen species (ROS), albeit via mechanistically distinct pathways (vide infra). The ROS are thought to be responsible, at least in part, for the observed biological activity of MGd and MLu [22],... 

The cadmium(II) complex corresponding to 9 (M = Cd n = 2) was the first texaphyrin made [6], This aromatic expanded porphyrin was found to differ substantially from various porphyrin complexes and it was noted that its spectral and photophysical properties were such that it might prove useful as a PDT agent. However, it was also appreciated that the poor aqueous solubility and inherent toxicity of this particular metal complex would likely preclude its use in vivo [29-31], Nonetheless, the coordination chemistry of texaphyrins such as 9 was soon generalized to allow for the coordination of late first row transition metal (Mn(II), Co(II), Ni(II), Zn (II), Fe(III)) and trivalent lanthanide cations [26], This, in turn, opened up several possibilities for rational drag development. For instance, the Mn(II) texaphyrin complex was found to act as a peroxynitrite decomposition catalyst [32] and is being studied currently for possible use in treating amyotrophic lateral sclerosis. This work, which is outside the scope of this review, has recently been summarized by Crow [33],... 

Many aza-crown macrocydic ligands [118] have been used to produce stable, well-shielded lanthanide complexes that have good photophysical properties. The aza-crown macrocydic ligand 19 has a terpyridine moiety incorporated into it to act as a sensitiser. Quantum yields of 0 = 0.18 and 0 = 0.21 were determined in water for the Eu(III) and Tb(III) complexes respectively. 19 is an... 

Due to the modifications of the electronic cloud induced by complexation, the quantum yield and the excitation spectrum are also modified. As the direct determination of the absolute quantum yield is very difficult to achieve, one usually finds in the literature quantum yield values determined by comparison to well-known standards, such as quinine sulfate. For example, some values can be found in Georges (1993) or in Klink et al. (2000) for some europium complexes but may be found also in many other papers on lanthanide luminescence. Studies on the correlations between the photophysical properties of a given type of europium complexes and the energy levels can be found in Latva et al. (1997), Klink et al. (2000). A correlation has been found between the excitation properties and the stoichiometry of various Eu(III) complexes (Choppin and Wang, 1997). Note that the changes in the excitation maximum induced by complexation usually amount to a few tenths of nanometers, which requires high resolution for detection. In the case of Eu(III), a correlation has been found between the frequency... 

Because of the higher sensitivity of Ndm ions towards deactivation through O-H oscillators, the complexes with this lanthanide have much lower quantum yields and lifetimes when compared to Ybm. The best photophysical properties are obtained with phthalexon S and since complexes with PS contain 4-5 water molecules, depending on the lanthanide ion, it is quite clear that exclusion of these water molecules from the first coordination sphere will lead to much enhanced luminescent properties. This is indeed demonstrated by bis(cyclen)-substituted PS, H736 (see fig. 36), which increases quantum yields to 0.23 and 1.45% in D2O for Ndm and Ybm, respectively (Korovin and Rusakova, 2002). 

In this chapter, different properties of nonlinear behavior in lanthanide complexes have been overviewed, including brief examination of their optical emission and excitation spectra. A perception of the importance of photophysical relationships of molecular complexes to these phenomena has also been conveyed. 

Lam, A.W.-H., Wong, W.T., Gao, S., Wen, G, and Zhang, X.-X. (2003) Synthesis, crystal structure, and photophysical and magnetic properties of dimeric and polymeric lanthanide complexes with benzoic acid and its derivatives. European Journal of Inorganic Chemistry, 149-163. 

Figure 4.21 The structure of [Lu(19)2](CH30H)(H20)] + [37]. (Reproduced with permission from C. Piguet, A.R Williams, C. Bemardine and J.C.G. Btinzli, Structural and photophysical properties of lanthanide complexes with planar aromatic tridentate nitrogen ligands as luminescent building blocks for triple-helical structures, Inorganic Chemistry, 32, 4139, 1993. 1993 American Chemical Society.)...

Using hexadentate tris[3-(2-pyridyl)pyrazol-l-yl]hydroborate (34) or tetradentate bis[3-(2-pyridyl)pyrazol-l-yl]dihydroborate (35) as a ligand, Ward and coworkers reported the preparation, characterization, and photophysical properties of a series of binary or ternary complexes of lanthanide(III) complexes with dibenzoylmethane anions (dbm) or nitrate anion as a co-ligand [58-60]. Sizeable NIR emission was detected for these pyrazolylborate-derived complexes of Nd(III), Pr(III), Er(III), and Yb(III) ions. They gave longer lifetimes of lanthanide luminescence than those of aminocarboxylate complexes due to the lack of C-H oscillators in close proximity to the lanthanide(III) ions in the pyrazolylborate complexes compared with that in the aminocarboxylate species. 

The preparation, characterization, aqueous stability, and photophysical properties of NIR emitting lanthanide complexes with tetradentate chelating ligands 36 and 37 were described by Raymond and coworkers [61, 62]. In aqueous solution, the chelating ligand 36 or 37 forms stable complexes with Ln(III) ions, and sensitized NIR lanthanide luminescence was detected for the complexes with Pr(III), Nd(III), Ho(III), or Yb(III) ions. For [Ln(36)2] complexes, the luminescence decay curves were biexponential due to partial hydrolysis of the complexes or alternately the presence of a slowly exchanging equilibrium mixture with a hydrated form of the complexes. For [Ho(37)2] , the NIR band due to Fs -> I transition of the Ho(III)... 

The photophysical properties of the triple-stranded dimetallic helicates [Ln2(41)3] (Ln=Nd, Sm, Dy, Yb) were investigated in water and D2O solutions by Biinzil and coworkers [64]. Lanthanide-centered luminescence is well sensitized in the triple stranded homodimetallic helicate complexes. The absolute quanmm yield of the ligand-centered luminescence decreases dramatically upon formation of the lanthanide helicates because of a significant enhancement... 

Figure 13.4 Typical design principle of lanthanide complex-based chemosensors based on binding of an analyte (an) (a) directly influencing the Ln(III) luminescence, (b) influencing photophysical properties of the ligand, and (c) addition of a sensitizing analyte onto a poorly luminescent lanthanide-containing sensor [1]. (Reproduced from J.C.G. Bunzli and C. Piguet, Taking advantage of luminescent lanthanide ions, Chemical Society Reviews, 34, 1048-1077, 2005, by permission of The Royal Society of Chemistry.)...

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