Mechanistic aspects of the photochemistry of [CpM(η6-arene)]+ complexes of Fe, Ru and Os
The photochemical displacement of q6-arenes from CpM(q6- arene)+ complexes (M=Fe, Ru, 0s) involves excitation to produce reactive, d-d excited states. The reactivity of these complexes decreases in the order Fe > Ru >Os for simple methyl substituted arenes. The quantum yields of these photoreactions indicate a significant associative component in the mechanism of arene release. The quantum yields for Fe complexes can be vaned by 105 by changing the steric hindrance, the solvent nucleophilicity and the nature of the counterion. The synthesis, photochemical and photophysical properties of CpRu(qb-arene)+ complexes (arene = rubrene, 9-phenylanthracene, coumarin laser dyes) have been investigated. In several cases (rubrene, 9-phenylanthracene) emissive and non-emissive isomers are produced. CpRu(q6-arene)+ complexes that exhibit fluid solution emission have metal complexation of a pendant rather than "chromophore" arene ring. Photochemical arene decomplexation ahd emission quantum yields for the CpRu+ complexes of substitued coumarins, rubrene, and 9- phenylanthracene show that the reaction and emission quantum yields are inversely related. When the photo-active d-d states are below the emissive arene chromophore in energy, arene displacement is observed; when the arene localized chromophore energy is lowest, emission from the complex is observed.