Journal of the American Chemical Society
ARTICLE
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stranded helicate [Ln2(L3)3]6+, while the macromonocyclic double-
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(30) 26ꢀ< α < 34ꢀ were found in the crystal structure of L3 3CHCl3.12
3
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(46) The π-delocalized didentate hfacꢀ counter-anions also possess
ligand-centered excited states which may contribute to the global
sensitization process in [Ln2(Lk)(hfac)6]. This assumption is demon-
strated by the absorption spectrum of the starting metallic complex
[Gd(hfac)3(diglyme)], which exhibits an intense absorption band
centered at 33060 cmꢀ1 (ε = 33 300 Mꢀ1 cmꢀ1, Figures 8 and S11)
that is assigned to the hfac-centered πfπ* transitions. Irradiation of
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E. B.; Verhoeven, J. W. J. Am. Chem. Soc. 1995, 117, 9408–9414.
[Gd(hfac) (diglyme)] at ν = 32 790 cmꢀ1 produces both faint
̅
3
exc
fluorescence (E(1ππ*) = 26 320 cmꢀ1, Figure S12a) and weak
16233
dx.doi.org/10.1021/ja206806t |J. Am. Chem. Soc. 2011, 133, 16219–16234