65013-13-0Relevant articles and documents
Femtosecond time-resolved photo-absorption studies on the excitation dynamics of chromium(III) porphyrin complexes in solution
Inamo, Masahiko,Okabe, Chie,Nakabayashi, Takakazu,Nishi, Nobuyuki,Hoshino, Mikio
, p. 167 - 172 (2007)
The electronic relaxation dynamics of the excited states of the chromium(III) tetraphenylporphyrin complexes, [Cr(TPP)(Cl)(L)] (L = H2O, pyridine, 1-methylimidazole), in toluene were studied by using femtosecond time-resolved absorption spectroscopy. The excited state (4T1) of 1-methylimidazole and pyridine complexes given by a very rapid intersystem crossing from 4S1 to 4T1 decays to establish the 4T1 ? 6T1 equilibrium in several hundred picoseconds. The 4T1 state of [Cr(TPP)(Cl)(H2O)] exhibits a biexponential decay composed of the photodissociation process of the axial H2O ligand and the decay of the photolyzed intermediate to the ground state of [Cr(TPP)(Cl)].
Laser photolysis of chromium(III) porphyrins with axial pyridines in dichloromethane and toluene solutions. Novel effects of a hydrogen bond in the ligand exchange reaction
Inamo, Masahiko,Nakaba, Hideyuki,Nakajima, Kiyohiko,Hoshino, Mikio
, p. 4417 - 4423 (2008/10/08)
Laser photolysis studies were carded out for (chloro)(pyridine)(5,10,15,20-tetraphenylporphyrinato)chromium-(III), [Cr(TPP)(Cl)(Py)], in both dichloromethane and toluene containing water. The five-coordinate [Cr(TPP)(Cl)] produced by the photoinduced dissociation of pyridine from [Cr(TPP)(Cl)(Py)] initially reacts with H2O to give [Cr(TPP)(Cl)(H2O)], which eventually exchanges the axial H2O with Py to regenerate [Cr(TPP)(Cl)(Py)]. The rate for the ligand exchange of [Cr(TPP)(Cl)(H2O)] with exogenous Py is found to exhibit a bell-shaped pyridine-concentration dependence. Kinetic studies revealed that at a high Py concentration, the exogenous Py probably makes a hydrogen bond with the axial H2O of [Cr(TPP)(Cl)(H2O)] to yield [Cr(TPP)(Cl)(HO-H···Py)] as a dead-end complex. A similar structure of the Cr-TPP complex having 2-methylpyridine molecules bound to the coordinated H2O ligand by a hydrogen bond was determined by X-ray structure analysis. The exchange reaction of the axial HO-H···Py in [Cr(TPP)(Cl)(HO-H···Py)] by Py follows the dissociative mechanism: The first step is the dissociation of Py from [Cr(TPP)(Cl)(HO-H···Py)], and the second step is the dissociation of H2O. The five-coordinate [Cr(TPP)(Cl)] thus produced reacts with Py to regenerate [Cr(TPP)(Cl)(Py)]. The direct ligand exchange reaction of the axial HO-H···Py in [Cr(TPP)(Cl)(HO-H···Py)] with exogenous Py does not occur. Probably, the hydrogen bond, HO-H···Py, increases the basicity of H2O, and thus, the bond energy between Cr and O in [Cr(TPP)(Cl)(HO-H···Py)] becomes much stronger than that in [Cr(TPP)(Cl)(H2O)]. The mechanism of the ligand substitution reaction of the chromium(III) porphyrins has been examined in detail on the basis of the laser photolysis studies of [Cr(TPP)(Cl)(L)] (L = pyridine, 3-cyanopyridine, and H2O).
Spectroscopic studies on some pyridine and morpholine adducts of (meso-tetraphenylporphyrin)chromium(III) chloride
Roe,Hill,Magee
, p. 1377 - 1383 (2007/10/02)
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