Stereoisomers of Mono-, Di-, and Triruthenium(II) Complexes Containing the Bridging Ligand 1,4,5,8,9,12-Hexaazatriphenylene and Studies of Their Photophysical Properties

A combination of synthetic methods involving mononuclear precursors of predetermined chirality {Δ- or Λ-[Ru(pp)2(CO)2]2+; pp = 2,2‘-bipyridine or 1,10-phenanthroline} and chromatographic techniques has allowed the isolation of the meso (ΔΛ) and rac (ΔΔ/ΛΛ) diastereoisomers of the dinuclear complexes [{Ru(pp)2}2(μ-HAT)]4+ {HAT = 1,4,5,8,9,12-hexaazatriphenylene}. The enantiomers of the rac forms have been separated, and characterization of all species has been achieved by NMR and CD studies. Additonally, the homochiral (Δ3/Λ3) and heterochiral (Δ2Λ/Λ2Δ) diastereoisomers of the trinuclear complexes [{Ru(pp)2}3(μ-HAT)]6+, and the enantiomers of both forms, have been isolated and identified. Emission studies of all the dinuclear species at room temperature indicate the relative luminescence quantum yields and the emission lifetimes significantly decrease for the meso compared with the rac diastereoisomers. No significant differences were detected at room temperature in the diastereoisomeric forms of the trinuclear compounds. However, in a glass at low temperature (80 K), the luminescence lifetimes of the trinuclear heterochiral diastereoisomer were slightly shorter than those of the homochiral form.