A Molecular Tetrad Allowing Efficient Energy Storage for 1.6 s at 163 K

Abstract

In a novel molecular ferrocene−zinc porphyrin−zinc porphyrin−fullerene (Fc−ZnP−ZnP−C60) 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 (∼1 s) of the bacteriochlorophyll dimer radical cation ((Bchl)2•+)−secondary quinone radical anion (QB•-) 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−C60•- 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−C60 relative to the corresponding ferrocene−zinc porphyrin−free base porphyrin−fullerene (Fc−ZnP−H2P−C60) tetrad.