Journal
JOURNAL OF PHYSICAL CHEMISTRY A
Volume 116, Issue 32, Pages 8321-8333Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp304667t
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Funding
- Department of the Defense
- Defense Threat Reduction Agency [HDTRA1-09-1-0005]
- National Science Foundation [CHE-0846235]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [846235] Funding Source: National Science Foundation
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We report evidence for the formation of long-lived photoproducts following excitation of iron(III) tetraphenylporphyrin chloride ((FeTPPCl)-T-(III)) in a 1:1 glass of toluene and CH2Cl2 at 77 K. The formation of these photoproducts is dependent on solvent environment and temperature, appearing only in the presence of toluene. No long-lived product is observed in neat CH2Cl2 solvent. A 2-photon absorption model is proposed to account for the power-dependent photoproduct populations. The products are formed in a mixture of spin states of the central iron(III) metal atom. Metastable six-coordinate high-spin and low-spin complexes and a five-coordinate high-spin complex of iron(III) tetraphenylporphyrin are assigned using structure-sensitive vibrations in the resonance Raman spectrum. These species appear in conjunction with resonantly enhanced toluene solvent vibrations, indicating that the Fe-(III) compound formed following photoexcitation recruits a toluene ligand from the surrounding environment. Low-temperature transient absorption (TA) measurements are used to explain the dependence of product formation on excitation frequency in this photochemical model. The six-coordinate photoproduct is initially formed in the high-spin Fe-(III) state, but population relaxes into both high-spin and low-spin state at 77 K. This is the first demonstration of coupling between the optical and magnetic properties of an iron-centered porphyrin molecule.
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