Femtosecond time-resolved photo-absorption studies on the excitation dynamics of chromium(III) porphyrin complexes in solution

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)].