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Issue 45, 2010
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First observation in the gas phase of the ultrafast electronic relaxation pathways of the S2 states of heme and hemin

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Abstract

The time evolution of electronically excited heme (iron II protoporphyrin IX, [FeII PP]) and its associated salt hemin (iron III protoporphyrin IX chloride, [FeIII PP–Cl]), has been investigated for the first time in the gas phase by femtosecond pumpprobe spectroscopy. The porphyrins were excited at 400 nm in the S2 state (Soret band) and their relaxation dynamics was probed by multiphoton ionization at 800 nm. This time evolution was compared with that of the excited state of zinc protoporphyrin IX [Zn PP] whose S2 excited state likely decays to the long lived S1 state through a conical intersection, in less than 100 fs. Instead, for [FeII PP] and [FeIII PP–Cl], the key relaxation step from S2 is interpreted as an ultrafast charge transfer from the porphyrin excited orbital π* to a vacant d orbital on the iron atom (ligand to metal charge transfer, LMCT). This intermediate LMCT state then relaxes to the ground state within 250 fs. Through this work a new, serendipitous, preparation step was found for FeII porphyrins, in the gas phase.

Graphical abstract: First observation in the gas phase of the ultrafast electronic relaxation pathways of the S2 states of heme and hemin

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Publication details

The article was received on 26 May 2010, accepted on 17 Aug 2010 and first published on 15 Oct 2010


Article type: Paper
DOI: 10.1039/C0CP00687D
Phys. Chem. Chem. Phys., 2010,12, 14985-14993

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    First observation in the gas phase of the ultrafast electronic relaxation pathways of the S2 states of heme and hemin

    M. Ha-Thi, N. Shafizadeh, L. Poisson and B. Soep, Phys. Chem. Chem. Phys., 2010, 12, 14985
    DOI: 10.1039/C0CP00687D

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