Research on Chemical Intermediates, 12 (1989) 203-216 203 Elsevier Science Publishers B.V., Amsterdam — Printed in The Netherlands FORMATION OF PHOTOCHEMICAL 7r-CATION RADICALS I. p-OXO-IRON (III) TETRAPHENYLPORPHYRIN C.R. GUEST, K.D. STRAUBt AND P.M. RENTZEPIS* Department of Chemistry University of California, Irvine Irvine, California U.S.A., 92717 and tVeterans Administration Medical Center and University of Arkansas for Medical Sciences Little Rock, Arkansas U.S.A., 72205 (Received 21 July 1989; accepted 30 July 1989) ABSTRACT We have monitored the spectra and kinetics of p-oxo iron (III) tetraphenyl porphyrin. The spectral changes between 460 nm and 770 nm were observed after excitation with 25 ps fwhm, 355 nm pulse. Ki- netic studies from —100 ps to 4 ns suggest that after the immediate formation of the excited states a transient species is formed which we assign to the 7r-cation radical-ferrous porphyrin pair. This pair decays with a time constant of 600 ps + 100 ps leaving a small amount of disproportionation reaction photoproducts. The spectra and kinetics of the transients, were not altered by concentration (0.15 OD - 1.0 OD at 571 nm), solvent or addition of oxygen. 0922-6168/89/$03.50 © 1989 Elsevier Science Publishers B.V.