Photoinduced electron transfer from a higher excited state of a porphyrin in a zinc porphyrin-ruthenium(II) tris-bipyridine dyad

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 S-2) 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 S-2 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 S-2 State occurred with a rate constant of 6 x 10(11) s(-1).