Osmium complex, luminescence

A dendrimer with metal complexes both in the core and in the branches was described by Balzani et al. The luminescent, heteroleptic (having different ligands), dendritic polypyridine-ruthenium or polypyridine-osmium complex can be prepared both divergently and convergently [130] (cf. Section 2.5.2). 

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). 

There are a number of osmium(VI) oxo complexes containing cyanide ligand, but none have been reported for ruthenium. The ion [0s(0)2(CN)4] can be prepared by reaction of [OSO4] with aqueous KCN. The X-ray crystal structure of Cs2[Os(0)2(CN)4] (85) shows that it has trans-6ioxo groups with 0s=0 distances of 1.750 [0s(0)2(CN)4] is luminescent both in the solid state... 

Tor and co-workers have developed a strategy for appending ruthenium(II) and osmium(II) polypyridyl complexes to nucleotides, by using succinimide esters as shown in Fig. 31 (197). These have been shown to incorporate into DNA without altering the global conformation, and still exhibit metal-centered luminescence (198). 

Balzani et al. prepared dendrimers with metal complexes serving both as core [36] and as branching unit The metallodendrimer in Fig. 2.10 is constructed solely from polypyridine ligands and transition metal ions. Such dendritic transition metal complexes can be synthesised both convergently and divergently and different transition metal ions (ruthenium/osmium) can be incorporated. This provides a means of influencing the luminescence properties of the den-drimer. Thus the energy transfer process proceeds from the inside outwards in... 

Demas et al. described optical oxygen sensors using analogous osmium(II) complexes that have intense red absorptions and that can be excited with low-cost, high-intensity red diode lasers [25]. The osmium(II) complexes are probably more photochemically robust than ruthenium(II) complexes because of the larger energy gap between emitting state and the photochemically destructive upper d-d state. In Table 2, the photochemical and photophysical properties of osmium(II) tris(l,4-diphenyl-l,10-phenanthroline) (Os(dpp)3+) and osmium(II) tris(l,10-phenanthroline) (Os(phen)3+) are indicated as examples of osmium(II) complexes. The luminescence lifetimes of Os(dpp)3+ and Os(phen)3+ are 4.6 and 6.0 ns in dichloromethane solution,... 

The 1,2-dithienylethene unit has also been used to link together metal tris(bipyridyl) moieties including an unsymmetrical Ru(II)/Os(II) complex. In the open form luminescence from the MLCT state is observed with efficient energy transfer from ruthenium to osmium. However, the emission is quenched upon conversion to the closed form because of energy transfer to the photo-chromic 1,2-dithienylethene orbitals.55... 

Tor modified a 2/-deoxyuridine with an alkynyl moiety at the 5-position of the base, and coupled it to ruthenium(II) and osmium(II) complexes with a 3-bromo-l,10-phenanthroline ligand to produce nucleosides (5) [33]. The ruthenium(II) nucleoside emits at 633 nm with a lifetime of 1.1 ps and a luminescence quantum yield of 0.051 in degassed aqueous solutions, while the osmium(II) analogue shows lower-energy and much weaker emission (A.em = 754 nm, tq = 0.027 ps, (Pcm = 0.0001). Phosphoramidites equipped with these... 

Barigelletti F et al (1993) Luminescence properties of rigid rod-like binuclear ruthenium(II)-osmium(II) terpyridine complexes - electronic interaction through phenyl bridges. JCS Chem Commun 942-944... 

Aromatic amine complexes65 of osmium, and also complexes of N macrocycles, are generally similar to those of Ru, but [Os(bipy)3]2+ and [Os(terpy)2]2+ are more labile and reactive than their Ru analogues. As for Ru, some Os11 complexes are luminescent and potentially of use in photochemical molecular devices and for detection of DNA.66... 

Sullivan reported the photophysical properties of the luminescent osmium alkylidyne complex... 

A number of luminescent osmium(II) and iridium(III) complexes have also been successfully used as photosensitizers. 

Irradiation at 300 nm in CCl, CHCl, or CH2CI2 promotes am irreversible reaction and formation of what is probably [Os(IV)(TTP)Cl2l. Optimum conditions have been reported for determination of osmium by measurement of the luminescence of its 1 3-complex with 1,10-phenanthroline.A catalyst, prepared by reducing the product of grafting OsO on to the C-C bond of sepiolite, has been found to mediate the photooxidation of water but to do so less efficiently than RuOjj. This is the first exaunple of a dispersed water oxidation catalyst grafted on to a solid support. 

Ruthenium and Osmium.—The quenching of the luminescent excited state of [Ru(bipy)3]8+ has continued to receive attention.72-78 As discussed in last year s Report, controversy exists as to whether this process for Co111 complexes proceeds via electron-transfer (20) or energy-transfer (21). Navon and Sutin72 have obtained... 

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