A molecular tetrad allowing efficient energy storage for 1.6 s at 163 K

In a novel molecular ferrocene-zinc porphyrin-zinc porphyrin-fullerene (Fc-ZnP-ZnP-C-60) tetrad, the longest lifetime of a charge-separated state ever reported in an artificial photosynthetic reaction center (1.6 s in DMF at 163 K) has been attained. This lifetime is comparable, for example, to the lifetime (similar to1 s) of the bacteriochlorophyll dimer radical cation ((Bchl)(2)(.+))-secondary quinone radical anion (Q(B)(.-)) ion pair in the bacterial photosynthetic reaction centers. The present far distant radical ion pair is formed with a quantum yield of 34%. The radical ion pair Fc(+)-ZnP-ZnP-C-60(.-) produced by photoinduced electron transfer was detected by means of transient absorption spectra as well as ESR spectra. Both the lifetime and the quantum yield of the final charge-separated state are improved in Fc-ZnP-ZnP-C-60 relative to the corresponding ferrocene-zinc porphyrin-free base porphyrin-fullerene (Fc-ZnP-H2P-C-60) tetrad.