MECHANISTIC ASPECTS OF THE PHOTOCHEMISTRY OF [CPM(ETA-6-ARENE)]+ COMPLEXES OF FE, RU AND OS

The photochemical displacement of eta6-arenes from CpM(eta6-arene)+ co mplexes (M=Fe, Ru, Os) involves excitation to produce reactive, d-d ex cited 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 i n the mechanism of arene release. The quantum yields for Fe complexes can be varied by 10(5) by changing the steric hindrance, the solvent n ucleophilicity and the nature of the counterion. The synthesis, photoc hemical and photophysical properties of CpRu(eta6-arene)+ complexes (a rene = rubrene, 9-phenylanthracene, coumarin laser dyes) have been inv estigated. In several cases (rubrene, 9-phenylanthracene) emissive and non-emissive isomers are produced. CpRu(eta6-arene)+ complexes that e xhibit fluid solution emission have metal complexation of a pendant ra ther than ''chromophore'' arene ring. Photochemical arene decomplexati on and emission quantum yields for the CpRu+ complexes of substitued c oumarins, rubrene, and 9-phenylanthracene show that the reaction and e mission quantum yields are inversely related. When the photo-active d- d states are below the emissive arene chromophore in energy, arene dis placement is observed; when the arene localized chromophore energy is lowest, emission from the complex is observed.