Ruthenium complex, luminescence

T. Hasegawa, T. Yonemura, K. Matsuura, and K. Kobayashi, Tris-bipyridine ruthenium complex-based glyco-clusters Amplified luminescence and enhanced lectin affinities, Tetrahedron Lett., 42 (2001) 3989-3992. 

The anthraquinone exhibits a similar redox behavior as benzoquinone. Thus, redox luminescence switch can also be constructed with fluorophore linked to anthraquinone. For example, the luminescence of molecule 22, a ruthenium complex with an appended anthraquinone moiety, can be reversibly tuned through the interconversion between the anthraquinone and the corresponding hydroquinone.32... 

Ruthenium(II) bipyridyl and Cr(III) aquo complexes luminesce strongly when photostimulated. The emission of light can be quenched effectively by such species as oxygen, paraquat, Fe(II) aquo complexes, Ru(II) complexes and Cr(NCS)i (Sutin [15]). Pfeil [16] found that the quenching rate coefficients are typically a third to a half of the value which might be predicted from the Smoluchowski theory [3]. 

Figure 19-18 Response of "molecular light switch" to immunoglobulin E (IgE). Aptamer concentration is 5 nM and ruthenium complex concentration is 40 nM. Addition of IgE displaces the ruthenium complex from the aptamer and decreases luminescence at 610 nm. Excitation wavelength = 450 nm.

Chiral ruthenium complexes, with luminescence characteristics indicative of binding modes, and stereoselectivities that may be tuned to the helix topology, may be useful molecular probes in solution for nucleic acid secondary structure36). 

Ruthenium complexes have been applied successfully to the luminescent detection of proteins on blotting membranes like nitrocellulose [160]. The bipyridyl and phenanthroline complexes modified with aminoreactive NHS-ester or isothiocyanate groups are commercially available [161]. An even higher sensitivity and lower detection limit can be obtained by encapsulating... 

A relatively large number of organic lumiphores and luminescent polypyridyl ruthenium complexes have been developed as luminescent pH probe molecules (82-84). The heterocyclic-substituted platinum-1,2-enedithiolates have also been developed in this regard (18, 19). 

Noted that it is essential that the polymers used to immobilize the emitter be amenable to the application (44, 47, 50-52). An additional factor that plagues both luminescent polypyridyl ruthenium complexes and the 2- or 4-pyridine substituted platinum 1,2-enedithiolate in this application is the oxygen-induced triplet quenching. 

The luminescence of the hybridized [Ru(phen)2(dppz)]2+ derivative may be used to characterize the molecular assembly (77). Dilution experiments show that intercalation is intramolecular at concentrations <5 mM duplex addition of unmodified duplex to the covalently bound duplex results in <5% change in the luminescence. The results of experiments performed on duplexes containing mismatches in various positions along the duplex are also consistent with intramolecular intercalation. In this series, luminescence is higher for mismatches near the ruthenated end of the oligomer, where the ruthenium complex can intercalate intramolecularly and stabilize the mismatched site. 

The emission spectmm of the H2(TRPyPz) species is characterized by the porphyrazine luminescence at 720 nm, while the excitation profile practically coincides with the absorption spectra, reproducing even the MLCT band at 500 nm, of the peripheral ruthenium complexes. Such coincidence corroborates the occurrence of efficient energy-transfer processes from the ruthenium complexes to the porphyrazine center, in contrast to the related supramolecular tetrapyridyl derivatives. 

P-Cyclodextrines, appended to a ruthenium complex, have been employed as hosts for iridium and osmium complexes bearing adamantyl or biphenyl moieties, which form strong host-guest complexes with P-cyclodextrines (see Fig. 3). In such systems, photoinduced energy transfer can occur from the periphery, upon complexation of the iridium units, toward the central ruthenium acceptor, or switched in the other direction, from the ruthenium to the periphery when the osmium moieties are assembled (see Fig. 3) 42). The lowest excited state is in fact localized on the osmium center, while the highest luminescent excited state belongs to the iridium complex (see Fig. 3 right). 

Quenching of the ( CT)[Ru(bipy)3] by [Cr(bipy)]3 has been studied. This is via electron transfer to the Cr complex and a rapid back reaction. The ruthenium complex will also quench the 727 nm emission of the metal-centred doublet excited state of the chromium species, by a similar mechanism. Evidently both ligand- and metal-centred excited states can be quenched by bimolecular redox processes. A number of Ru complexes, e.g. [Ru(bipy)3] and [Ru(phen)3] also have their luminescence quenched by electron transfer to Fe or paraquat. Both the initial quenching reactions and back reactions are close to the diffusion-controlled limit. These mechanisms involve initial oxidation of Ru to Ru [equation (1)]. However, the triplet excited state is more active than the ground state towards reductants as well as... 

Ruthenium complexes used to lead research in photochemistry of metal compounds, but rhodium complexes have recently overtaken them as the key target compounds due to their applications in OLEDs. This is a lively and ever-changing field for example, over 90% of luminescent iridum(III) complexes have been reported only in the six years to the beginning of 2009. With their luminescence tuneable through ligand choice, iridium complexes are firm candidates for optical display applications. 

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