Broadband ultrafast transient absorption of iron (III) tetraphenylporphyrin chloride in the condensed phase

Ultrafast transient absorption of iron (III) tetraphenylporphyrin chloride [(FeTPPCl)-T-(III)] is used to probe the excited state relaxation in room temperature solution. The ground state was excited either at 400 nm near the Soret resonance or at 520 nm in the Q resonance. Relaxation from the lowest lying porphyrin singlet (pi, pi*) manifold results in formation of a LMCT (pi, d(pi)) state on a time scale of 0.4-0.6 ps followed by a metal-to-ligand charge transfer transition from the iron to the porphyrin on a time scale of 1.8-2.3 ps, producing an excited T-4 intermediate spin state of (FeTPPCl)-T-(III). The system relaxes back to the high spin (6)A(1) ground state on a time scale of 13-18 ps. The relatively slow electronic relaxation of the more symmetric (FeTPPCl)-T-(III) compound is contrasted with the much faster subpicosecond ground state recovery observed for less symmetric biologically active heme systems at room temperature. (C) 2013 Elsevier B. V. All rights reserved.