Rhenium complexes luminescent properties

A series of rhenium(I) complexes [Re(CO)3(N-N) ( C=C -R)] containing conjugated alkynyl ligands displayed remarkable luminescence properties. The origin of the... 

Zubieta and coworkers have recently taken advantage of the fluorescent and luminescent properties of organometallic complexes of rhenium (and technetium) comprising certain aromatic ligand systems (Fig. 2.2.6). The nonradioactive Re(CO)3 bioconjugates with a formyl peptide receptor-targeting peptide (flVlLF), enabeled visualization... 

The use of Tapy (l-(2-pyridyl)-l,2,3-triazole) ligand bearing long allqrl chains demonstrates an impressive enhancement of the luminescent properties of the rhenium complexes in aqueous medium relative to the parent Pyta complex." ... 

Rhenium (I) complexes of the general structure depicted in Fig. 6.7 have been shown to display remarkable photo luminescent properties since the 1970s [44, 45]. 

The enhancement of the luminescence properties of the rhenium(I) complexes has also been demonstrated by Belser and coworkers with a bis(anthracene)-functionalized bipyridine ligand (Figure 11). This rhenium complex did not show any MLCT phosphorescence as the emissive excited state was effectively quenched by the anthracene moieties. With the disruption of tt-conjugation through the reversible photoinduced [4-1-4] cycloaddition of the anthracene moieties, the lowest lying excited state of the cycUzed dimer could not quench the MLCT emission, leading to the enhancement of the luminescence properties. 

The luminescent properties evident in rhenium(I)tricarbonyl complexes arise from the metal-to-ligand charge transfer (MLCT) between the dir (Re) orbitals and the it orbitals on the corresponding chelate (342 nm). The emitting states. 

Lo and co-workers reported the synthesis, characterisation, photophysical and electrochemical properties of luminescent rhenium(I) diimine indole complexes [Re(N"N)(CO)3(py-indole)]+ (36) [75,76]. Upon visible-fight irradiation, the complexes exhibited 3MLCT (dTt(Re) —> Tt (N N)) emission in fluid solutions at 298 K and in low-temperature glass. When these com-... 

In the following sections, luminescent organometallic rhenium(I) and iridium(III) polypyridine complexes relying on the labelling or binding strategies mentioned above will be described. We focus on the molecular structures, spectroscopic and photophysical properties of the complexes, and the emissive behaviour and potential applications of the labelled bioconjugates. 

Other work has demonstrated that it is possible to switch ON and OFF luminescence by reduction/oxidation, and it has been demonstrated that such switching is possible inside an OTTLE cell. Many alkynyl complexes, especially those of rhenium, platinum,copper, silver or gold " are highly luminescent from their excited MLCT or metal perturbed 71 states. This opens up the possibility to significantly influence their emissive properties by redox processes. An interesting example is found in recent work of Wong et Unlike other rhenium(I)-alkynyl complexes, heterobimetallic... 

The robustness of the rhenium(i) diimine alkynyl systems and rich photophysical behavior have rendered them suitable as metalloligands for the synthesis of mixed-metal complexes. It is well-known that organometallic alkynes exhibit rich coordination chemistry with Cu(i), Ag(i) and Au(i) [214-218], however, photophysical properties of these r-coordinated compounds are rare. Recent work by Yam and coworkers has shown that luminescent mixed-metal alkynyl complexes could be synthesized by the metalloligand approach using the rhenium(i) diimine alkynyl complexes as the z -ligand. Reaction of the rhenium(i) diimine alkynyl complex [Re(bpy)(CO)3C=CPh] with [M(MeCN)4]PF6 in THF at room temperature in an inert atmosphere afforded mixed-metal Re(i)-Cu(i) or -Ag(i) alkynyl complexes (Scheme 10.31) [89]. Their photophysical properties have also been studied. These luminescent mixed-metal complexes were found to emit from their MLCT[d7i(Re) —> 7i (N N)] manifolds with emission bands blue-shifted relative to their mononuclear precursors (Table 10.5). This has been attributed to the stabilization of the dTi(Re) orbital as a consequence of the weaker t-donating ability of the alkynyl unit upon coordination to the d metal centers. 

A series of luminescent rhenium(I) triynyl complexes, Re(CO)3L(-C = C-C = C-C = CR) (L = Me2bpy or Bu 2bpy, R = Ph or SiMe3), have been prepared and their photophysical and electrochemical properties studied. Surprisingly, lengthening the carbon chain resulted in a blue shift in the emission energy of the complexes, rather than the expected red shift. 

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