Fullerene derivatives substituted with differently branched phenyleneethynylene dendrons:: Synthesis, electronic and excited state properties

Fullerene derivatives functionalized with isomeric phenyleneethynylene-based dendrons possessing either 1,3,5-tri-ethynylbenzene or 1,2,4-triethynylbenzene branching units have been prepared. The electrochemical properties of these compounds are not strongly dependent on the branching patterns since the corresponding redox processes are localized either on the C-60 cage (acceptor unit) or on the dialkyloxy-benzene moieties (donor units) at the dendron periphery. The photophysical investigations performed in CH2Cl2 have revealed an ultrafast dendron -> C-60 energy transfer in all these hybrid systems. Importantly, the different pi-conjugation patterns in the two series have a dramatic effect on their electronic properties as attested by the differences observed in their absorption and emission spectra. The lower lying absorption onset and the wider spectral profile of the dyads with 1,2,4-triethynylbenzene branching units when compared to their 1,3,5-triethynylbenzene analogues clearly points out an improved light harvesting capability. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 6945t Weinheim, Germany, 2007)