Photophysical properties centers

Attaching a Ceo cluster to an [Ru(bpy)3] + core has been achieved by 1,3-dipolar cycloaddition of azomethine ylides to the fullerene. The electrochemistry of the complex is complicated a one-electron reversible oxidation of the Ru center, five one-electron reversible reductions associated with the Ceo cage, and five more reversible reductions centered on the bpy ligands. The photophysical properties of the complex have been discussed. ... 

The fullerenes, in particular Cgg, exhibit a variety of remarkable photophysical properties, making them very attractive building blocks for the construction of photosynthetic antenna and reaction center models (Table 1.6) [292-295],... 

For those complexes where the chromophore is not coordinated to the metal center directly, the orientation of the chromophore is important to ensure efficient energy transfer. The series of ligands L29-L32 were investigated for correlations between structural parameters found in the solid state (see, for example, Fig. 12) and solution (by NMR spectroscopy) and photophysical properties (69,70). It was found that both chromophore-metal separation and the angle of orientation have a direct influence on the quantum yield of the europium complexes. For example, the difference in quantum yield between [Eu(L29)]3+ and [Eu(L30)]3+ (0.06 and 0.02, respectively) cannot be attributed solely to the chromophore-metal separation, so may also depend on the better orientation of the chromophore in the L29 system as measured by the angle a between the metal center, the amide nitrogen atom, and the center of the phenyl ring. 

In this work, we will review the optical, and to some extent, the electrochemical properties, of selected subfamilies of Ir(III) complexes. This will be done having in mind mainly (i) the actual interest in the manipulation and tuning of the photophysical properties of complexes playing as phosphorescence emitters, (ii) the possible use of Ir(III) centers as templating units for multicomponent arrays, particularly in view of charge separation (CS) schemes for the interconversion of light and chemical energy. 

In this section, we describe the construction of metal-containing polymers and supramolecular assemblies, in which metallic centers are linked by a bridging diisocyanide ligand along with their photophysical properties (Fig. 3). 

Sensitization of Ybm luminescence by tetraphenylporphyrinate 5c (TTP, fig. 12) is demonstrated by a dramatic drop in the quantum yields of the 1S i -level fluorescence of this species from 0.06% for [Lu(TTP)acac] to less than 3 x 10 3% for the Ybm derivative. In parallel, the quantum yield of the 1S2-level fluorescence diminishes from 0.15% (Lum) to 0.01% (Ybm). No quantum yield for the metal-centered luminescence is given in this initial work, but t(2F5/2) is reported to be equal to 5 ps (Tsvirko et al., 1980). The quantum yield of [Nd(TTP)acac] has been determined in benzene and is equal to 0.025% (Shushkevich et al., 1981). The latter authors have also measured the quantum yields of [Yb(OEP)acac] (0.045%) and [Yb(2c)acac] (0.054%) in the same solvent and undertaken a careful study of the polarization of Ndm and Ybm emission bands and discussed it with respect to the symmetry of the complexes. In order to improve the photophysical properties of [Er(TPP)acac] the complex has been dispersed at concentrations of 5, 17, 28, and 37 wt% into thin films of n-conjugated... 

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. 

As outlined above, the electrochemical properties of this redox species are strongly pH-dependent and this behavior can be used to illustrate the supramolecular nature of the interaction between the polymer backbone and the pendent redox center. The cyclic voltammetry data shown in Figure 4.17 are obtained at pH = 0, where the polymer has an open structure and the free pyridine units are protonated (pKa(PVP) = 3.3). The cyclic voltammograms obtained for the same experiment carried out at pH 5.7 are shown in Figure 4.18. At this pH, the polymer backbone is not protonated and upon aquation of the metal center the layer becomes redox-inactive, since protons are involved in this redox process. This interaction between the redox center and the polymer backbone is typical for these types of materials. Such an interaction is of fundamental importance for the electrochemical behavior of these layers and highlights the supramolecular principles which control the chemistry of thin films of these redox-active polymers. Finally, it is important to note that the photophysical properties of polymer films are very similar to those observed in solution. Since the layer thickness is much more than that of a monolayer, deactivation by the solid substrate is not observed. 

---