Luminescence NIR

Fig. 7 Spectral changes observed upon titration of a 4.2 x 10 6 M solution of dendrimer II by Nd(CF3S03)3. Left-hand side spectra refer to the quenching of the fluorescence of the dansyl units in the visible region and right-hand side spectra to the sensitization of the NIR luminescence of Nd3+...

The three complexes display NIR luminescence in addition to porphyrinate emission at 650 nm, although Er111 luminescence is again faint. In addition, the Nd111 porphyrinate proved to be photosensitive and decomposed under irradiation by the N2-laser (337 nm), so that its photophysical characteristic could not be determined. The lifetime of the Yb(2F5/2) level amounts to 2.43 ps, that is about ten times smaller than for [Yb(5d)TpH], Replacement of the water molecule with dmf when the porphyrinate is dissolved in this solvent results in an increase in the intensity of the metal-centered luminescence. 

The three Schiff-base bibracchial lariat ethers H2l7a-c derivatives have been designed for their ability to form a cryptand-like cavity upon reaction with Lnm ions, the size of which can be tuned by varying the number of -CH2-CH2-O- units in the macrocycle. The two 2-salicylaldiminobenzyl pendant arms fold in such a way that jt-jt interactions between aromatic rings result in the formation of a cryptand-like cavity, as demonstrated by the X-ray structure of the Cem complex with 17b depicted on fig. 25 (Gonzales-Lorenzo et al., 2003). The triplet state of the di-anionic receptor is located at 18750 cm-1 (0-phonon component measured on the Gd111 complex) so that sensitization of the NIR luminescence is not optimum nevertheless, Ndm emission could be detected. 

All the ternary Nd111 complexes, Nd(/i -dikct)3 (bath), formed with these ligands and with bath (monobathophenanthroline) exhibit the characteristic metal-centered NIR luminescence. The photophysical properties of these chelates are compared to those of [Nd(dbm)3(phen)] in table 9. 

X 109 and 8. 9 x 109 s 1 for Ndm and Ybm, respectively. Both the above-described in-termolecular mechanism, as well as an intramolecular pathway in the ternary complex with aad which forms in solution, are responsible for the observation of NIR luminescence in these systems. Addition of water to the toluene solutions quenches the NIR luminescence, while it enhances the visible CL emission of the corresponding solution of Eum and Tbm (Voloshin et al., 2000c). Neodymium and ytterbium tris(benzoyltrifluoroacetonates) display the same CL as tta complexes, although for Ybm its intensity is about 2.5 times lower than for the tta chelate. On the other hand, almost no CL is detected for acetylacetonate complexes (Voloshin et al., 2000a). Thermal or photochemical decomposition of aad also triggers CL from [Pr(dpm)3] and Pr(fod)3], both in the visible (from the 3Pi, 3Po, and 1D2 levels) and in the NIR at 850 nm ( Do -> 3F2 transition) and 1100 nm ( D2 3F4 transition). The excited... 

The complexes of general formula [Ln(61)] (Ln = Nd, Er and Yb) (see fig. 60) exhibit the typical NIR luminescence of each Lnm ion upon excitation in the antenna chromophore. The overall quantum yields have been determined in deuterated methanol and by using the Ndm... 

The three Ndm, Er111, and Ybm chelates display sizeable metal-centered NIR luminescence in HBS-buffered (pH 7.4) aqueous solutions. Their photophysical characteristics are summarized in table 18. The hydration numbers calculated from eqs. (10a) and (9a) are very small, 0.31 and 0.16 for Ndm and Ybm, respectively, and compare well with the results obtained for the tetrapodal ligand H890a. The overall luminescence quantum yields in aqueous solution are comparable to those obtained for H890a, but smaller than those determined for chelates withH890b (compare tables 17 and 18). Upon deuteration of the solvent, from 3- to 10-fold increases are observed in the luminescence quantum yields. Moreover cytotoxicity studies on several cell lines have shown the Ybm chelate to be non-toxic, opening the way for applications in cell imaging (Comby et al., 2007). 

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