Coordinative Interactions between Porphyrins and C_(60), La@C_(82), and La_2@C_(80)

摘要

For the first time, a C_(60) derivative (1) and two different lanthanum metallofullerene derivatives, La@C_(82)Py (2) and La_2@C_(80)Py (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 photophysical 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 logK_(assoc)=3.94- 4.38, are dominated by axial coordination, with minor contributions from the orbital overlap of the curved and planar p 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.