Coordinative Interactions between Porphyrins and C60, La@C82, and La2@C80

For the first time, a C-60 derivative (1) and two different lanthanum metallofullerene derivatives, La@C82Py (2) and La-2@C80Py (3), that feature a pyridyl group as a coordination site for transition-metal ions have been synthesized and integrated as electron acceptors into coordinative electron-donor/electron-acceptor hybrids. Zinc tetraphenylporphyrin (ZnP) served as an excited-state electron donor in this respect. Our investigations, by means of steady-state and time-resolved photo-physical techniques found that electron transfer governs the excited-state deactivation in all of these systems, namely 1/ZnP, 2/ZnP, and 3/ZnP, whereas, in the ground state, notable electronic interactions are lacking. Variation of the electron-accepting fullerene or metallofullerene moieties provides the incentive for fine-tuning the binding constants, the charge-separation kinetics, and the charge-recombination kinetics. To this end, the binding constants, which ranged from log K-assoc=3.94-4.38, are dominated by axial coordination, with minor contributions from the orbital overlap of the curved and planar pi systems. The charge-separation and charge-recombination kinetics, which are in the order of 10(10) and 10(8) s(-1), relate to the reduction potential of the fullerene and metallofullerenes, respectively.