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

Abstract The electronic relaxation dynamics of the excited states of the chromium(III) tetraphenylporphyrin complexes, [Cr(TPP)(Cl)(L)] (L = H 2 O, pyridine, 1-methylimidazole), in toluene were studied by using femtosecond time-resolved absorption spectroscopy. The excited state ( 4 T 1 ) of 1-methylimidazole and pyridine complexes given by a very rapid intersystem crossing from 4 S 1 to 4 T 1 decays to establish the 4 T 1  ⇌  6 T 1 equilibrium in several hundred picoseconds. The 4 T 1 state of [Cr(TPP)(Cl)(H 2 O)] exhibits a biexponential decay composed of the photodissociation process of the axial H 2 O ligand and the decay of the photolyzed intermediate to the ground state of [Cr(TPP)(Cl)].