Picosecond kinetics of copper and silver protoporphyrins

Abstract

By the use of the dual beam picosecond absorption spectroscopy technique, the initial events in the energy relaxation process of Cu(II) and Ag(II) protoporphyrin IX dimethyl esters were studied. The energy decay channels were found to be as follows. Cu(II) (Z=29) complex: After picosecond excitation, a Franck–Condon state of 2 S 1 is populated which decays into 2 T 1 within 8 psec. This state relaxes with a time constant of 450–460 psec to 2 T 1 and 4 T 1 equilibrium state from which phosphorescence is emitted. Ag(II) (Z=47) porphyrin: Picosecond excitation to the 2 S 1 state results in energy relaxation to 2 T 1 state within 8 psec which is followed by equilibration between 2 T 1 and 4 T 1 with a time constant of 11–12 psec. Subsequently the relaxation proceeds via nonradiative channels to 2 T d and 4 T d or 2(d,π*) states.