Photoinduced Electron Transfer from a Higher Excited State of a Porphyrin in a Zinc Porphyrin−Ruthenium(II) <i>tris</i>-Bipyridine Dyad

Abstract

Pump−probe spectroscopy and steady state emission measurements have been used to demonstrate electron transfer from the excited state populated by excitation in the Soret band (denoted S2) of a zinc porphyrin to a covalently linked ruthenium(II) tris-bipyridine complex (ZnTTP-L-Ru(bpy)3). The lifetime of 1.6 ps measured for the S2 state of the zinc porphyrin (ZnTTP) was reduced to 0.8 ps in the dyad. On the basis of fluorescence data and transient absorption spectra, energy transfer from the porphyrin to the ruthenium was found to be negligible. Instead, electron transfer from the S2 state occurred with a rate constant of 6 × 1011 s-1.