Mixed photophysical properties

Other first-generation dendrimers built around multichelating ligands are the trinuclear complexes 29 - 38 [50-52] and several hexanuclear complexes (for representative examples, see 39 and 40) [53]. In all of these compounds, the photophysical properties are equivalent to those of their building blocks. In the mixed-metal complexes 31 and 34 [50b] the Ru(II)- and Os(II)-based chromo-phores are only weakly-coupled and a dual luminescence is observed. 

D.A.M. Egbe, S. Sell, C. Ulbricht, E. Birckner, and U.-W. Grummt, Mixed alkyl- and alkoxy-substituted poly[(phenylene ethynylene)-a/t-(phenylene vinylene)] hybrid polymers synthesis and photophysical properties, Macromol. Chem. Phys., 205 2105-2115, 2004. 

These compounds are readily prepared by the reaction of fluorescein isothiocyanate with the polypeptide in a DMSO/water mixture and fluorescein-polyacrylate conjugate (6) is prepared by the reaction of fluoresceinamine with polyacrylic acid by using the mixed anhydride method [150]. In all cases, the absorption and emission maxima were similar at 490 and 525 nm, respectively, and reflect the photophysical properties of fluorescein itself. 

Table 1 Room temperature (RT) photophysical properties of mixed imine/carbonyl complexes of Os(II)...

Note that the combined mixing coefficient a b determines the radiative rate given by (32) (compare (28), (29), and (30)). According to (31) and (32), two matrix elements, one for Cl and one for SOC, and two energy denominators determine the photophysical properties of the lowest triplet substate. As consequence, these indirect SOC paths to the substates of a 3LC state have less influence on the ZFS and the radiative decay rates than direct SOC to the substates of a 3MLCT. 

A great number of studies have addressed the photophysical properties of related Zn(diimine)(SR)2 complexes. Crosby and co-workers (136, 137) investigated many mixed-ligand complexes of Zn(II) and Cd(II) containing diimine ligands and monodentate aromatic thiolate ligands. They note that the rotational... 

One of the basic goals in polymer science is to identify the nature of the local environmental domains (viscosity, hydrophobicity, etc.) domains within a polymer solid or solution. This may be accomplished by using a variety of photophysical techniques all of which involve mixing or covalently attaching a small amount of a luminescent molecule (probe) into a polymer system. The probe molecule is designed such that one or more of its photophysical properties is directly dependent on some aspect of its environment. For example, both the fluorescence lifetime and the relative intensities of the vibrational structure of pyrene are altered when exposed to an aqueous, as opposed to a hydrophobic, medium. Polyelectrolytes such as poly(acrylic acid), under the proper... 

Another extremely useful method for cac determination, especially in the light of high sensitivity, is fluorescence emission spectroscopy [15]. Some aromatic water-insoluble dyes that are present in trace amounts in mixed polyelectrolyte-surfactant solutions have an ability to solubilize within the self-assembled surfactant aggregates and to change their photophysical properties because of the change of environmental polarity. Through this, they offer a very sensitive method for the determination of cac values. A typical and lately frequently used compound is pyrene, which is used as a fluorescence probe to assess various micellar properties. Pyrene exhibits a polarity dependent fluorescence spectrum with the ratio /,//3 (the ratio of the intensity... 

Cyclometallated Rh(III) complexes have long been known, but their photophysical properties have been investigated only recently. Particular interest has been devoted to mixed-ligand and binuclear complexes. 

For phosphorescence, lanthanide metal ions can be used in a similar manner. Lanthanide ions have very interesting photophysical properties, but often exhibit weak absorption bands, and aggregate to form clusters, which limit their applications. Thus, a dendrimer that can provide a protective shell to isolate a cation and at the same time enhance the emission by transfer from the periphery to the lanthanide ion at the core could be of great interest. Self-assembled lanthanide-cored dendrimers have been prepared to prove such an assumption synthesis was carried out by mixing three equivalents of polyaryl ether dendrons bearing carboxylic acid entity at the focal point with Ln(III) cations [Er(III), Tb(III), and Eu(III)] (Fig. 5.4) [34]. The authors demonstrated that the enhancement of the lanthanide cation emission associated with the dendritic core shell was observed, and an antenna effect from the periphery to the core was shown to promote this process. 

---