The ultrafast intramolecular dynamics of phthalocyanine and porphyrin derivatives

The internal conversion and intramolecular vibrational relaxation processes of nitro-tri-tert-butylphthalocyanine, tetra-phenylporphyrin (TPP), and tetra-tert-butylphthalocyanine (BuPc) in chloroform solution were investigated with an ultrafast time-resolved fluorescence depletion method. A regular fluorescence depletion was observed, indicating that the vibrational relaxation in the S1 state takes a few hundred femtoseconds to several picoseconds. For TPP and BuPc, an additional sharp dip superposes on the regular depletion. It is explained by an ultrafast internal conversion process from the S2 state to the S1 state with a time of a few tens of femtoseconds.