S2- and S1-states properties of zinc porphyrin polypeptides

S2- and S1-states properties of zinc porphyrin polypeptides were investigated using various fast spectroscopic techniques. The B band of zinc porphyrin polypeptides showed broadening and shift to the longer wavelength side with the polymerization degree, indicating the interaction between the porphyrin units. The lifetime of S2-fluorescence became shorter with increasing the polymerization degree. This phenomenon can be explained by applying the energy gap law to the S2–S1 internal conversion. From the picosecond transient absorption measurements, singlet–singlet annihilation was confirmed, indicating the intrachain singlet energy migration in the polypeptides. The annihilation rate became faster with the polymerization degree because of the shorter distance between the zinc porphyrin units of longer polypeptides.