Synthesis of Fullerohelicates and Fine Tuning of the Photoinduced Processes by Changing the Number of Addends on the Fullerene Subunits

Two fullerene-substituted m-phenylene-bis-phenanthroline ligands have been prepared. The synthesis of the first derivative (L1) is based on an esterification reaction between a C-s symmetrical cis-2 fullerene bis-adduct bearing a carboxylic acid function and a bisphenanthroline alcohol (5). The second ligand (L2) has been obtained by reaction of a bis-phenanthroline malonate (9) and C-60 under Bingel conditions. The copper(I) complexes of L1 and L2 have been prepared by treatment with a slight excess of Cu(CH3CN)(4)BF4. NMR spectroscopy and mass spectrometry analysis have unambiguously shown that these complexes are bis-copper(l) helicates substituted with two fullerene moieties. The photophysical properties of the copper(I) complexes Cu-2(L1)(2) and Cu-2(L2)(2) have been investigated. In both systems photoinduced electron transfer from the central metal-complexed unit to the external fullerenes may occur, in principle, by excitation of both moieties. However, this is found to be the case only for the methanofullerene system Cu-2(L2)(2). Unexpectedly, for Cu-2(L1)(2), photoexcitation of the peripheral carbon spheres is followed by regular internal deactivation. Possible reasons for this behavior are examined in light of current theories for photoinduced energy and electron transfer.