Mimicking photosynthetic antenna-reaction-center complexes with a (Boron Dipyrromethene)₃-Porphyrin-C₆₀ pentad

A highly efficient functional mimic of the photosynthetic antenna-reaction-center complexes has been designed and synthesized. The model contains a zinc(II) porphyrin (ZnP) core, which is connected to three boron dipyrromethene (BDP) units by click chemistry, and to a C₆₀ moiety using the Prato procedure. The compound has been characterized using various spectroscopic methods. The intramolecular photoinduced processes of this pentad have also been studied in detail with steady-state and time-resolved absorption and emission spectroscopic methods, both in polar benzonitrile and nonpolar toluene. The BDP units serve as the antennae, which upon excitation undergo singlet-singlet energy transfer to the porphyrin core. This is then followed by an efficient electron transfer to the C₆₀ moiety, resulting in the formation of the singlet charge-separated state (BDP)₃-ZnP ^.+-C₆₀^.-, which has a lifetime of 476 and 1000a ps in benzonitrile and toluene, respectively. Interestingly, a slow charge-recombination process (κ^T _CR=2.6×10⁶a s^-1) and a long-lived triplet charge-separated state (τ^T_CS=385 ns) were detected in polar benzonitrile by nanosecond transient measurements. Good combination! Covalent linkage of three boron dipyrromethene units, a zinc(II) porphyrin core, and a C₆₀ moiety results in the formation of a novel pentad (see figure) which can mimic the efficient processes of energy transfer followed by electron transfer occurring in photosynthetic antenna-reaction-center complexes.