Anions excited state complexes

The cation radical can undergo deprotonation to yield an allyl radical or nucleophilic attack by the solvent to produce a methoxyalkyl radical. Coupling of these radicals with the aromatic radical anion produces acyclic adducts. As an alternative, the anion radical can be protonated, ultimately giving reduction product. Thus, the degree of charge separation within the excited state complex dramatically influences the observable chemistry. 

The CT complex is usually considered as an excited-state complex with radical cation and radical anion character 02 ) [1169, 1170, 1185, 2139]. Such a CT complex formed in liquid monomeric hydrocarbons, ethers and alcohols can result in the formation of singlet molecular oxygen ( A ) [1943,1944]. The available data also suggest that, in certain polar solvents, the CT complex is in equilibrium with the solvated organic radical cation and the superoxide ion (0 2 ). Thus photolysis of the CT band can result in the formation of two independent and reactive forms of molecular oxygen ( Ag and 0 2 ). 

The primary reason for studying aqueous plutonium photochemistry has been the scientific value. No other aqueous metal system has such a wide range of chemistry four oxidation states can co-exist (III, IV, V, and VI), and the Pu(IV) state can form polymer material. Cation charges on these species range from 1 to 4, and there are molecular as well as metallic ions. A wide variety of anion and chelating complex chemistry applies to the respective oxidation states. Finally, all of this aqueous plutonium chemistry could be affected by the absorption of light, and perhaps new plutonium species could be discovered by photon excitation. 

In complex organic molecules calculations of the geometry of excited states and hence predictions of chemiluminescent reactions are very difficult however, as is well known, in polycyclic aromatic hydrocarbons there are relatively small differences in the configurations of the ground state and the excited state. Moreover, the chemiluminescence produced by the reaction of aromatic hydrocarbon radical anions and radical cations is due to simple one-electron transfer reactions, especially in cases where both radical ions are derived from the same aromatic hydrocarbon, as in the reaction between 9.10-diphenyl anthracene radical cation and anion. More complex are radical ion chemiluminescence reactions involving radical ions of different parent compounds, such as the couple naphthalene radical anion/Wurster s blue (see Section VIII. B.). 

As described earlier, the reactivity of photoinduced electron transfer is remarkably enhanced by the complexation of excited states with metal ions. Even if there is no direct interaction between excited states and metal ions, however, metal ions can enhance the reactivity of photoinduced electron transfer when the radical anion produced in photoinduced electron transfer binds with metal ions [11,12,25]. For example, although there is no direct interaction between the triplet excited state of Ceo ( Ceo ) and Sc(OTf)3, an efficient electron transfer occurs from Ceo to p-chloranil (CI4Q) to produce Ceo" and the p-chloranil radical anion CUQ -Sc complex [135]. In contrast to the facile reduction of Ceo,... 

Metal-to-hgand charge transfer (MLCT) systems are mostly based upon complexes of ruthenium and rhenium. The simplest and best known example of a MLCT lumophore is tris(2,2 -bipyridyl)ruthenium(ii) where photon absorption leads to an excited state composed of a centre and a radical anion on one of the bipyridyl units. 

Yasuda N, Uekusa H, Ohashi Y (2004) X-Ray analysis of excited-state structures of the diplatinum complex anions in five crystals with different cations. Bull Chem Soc Jpn 77 933-944... 

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