Photoinduced electron transfer in a supramolecular triad system composed of ferrocene-zinc porphyrin-pyridylnaphthalenediimide

A supramolecular ferrocene-zinc porphyrin-pyridylnaphthalenediimide triad is formed by coordinating the pyridine entity of pyridylnaphthalenediimide with the zinc ion of a ferrocene-zinc porphyrin dyad in benzonitrile. The fluorescence of the zinc porphyrin moiety is efficiently quenched by photoinduced electron transfer from the singlet excited state of the zinc porphyrin moiety to the naphthalenediimide moiety. This is followed by subsequent electron transfer from the ferrocene moiety to the zinc porphyrin radical cation to produce the final charge-separated state, ferricenium ion-zinc porphyrin-naphthalenediimide radical anion, which is successfully detected as a transient absorption spectrum in the laser flash photolysis. The decay of the charge-separated state obeys first-order kinetics irrespective of the initial concentration of the charge-separated state to afford a long lifetime (320 μs). This is the first example of a supramolecular triad that has a long lifetime as compared with the charge-separated state lifetime of the component dyad.