Luminescent Properties of Metal Porphyrin Reduction Products

We have investigated the luminescent properties of -anions in Zn and Pd complexes of octaethylporphin and etioporphyrin, and also of protonation products of -dianions (-monoanions of phlorins). It is established that the quantum yield of luminescence of -anion radicals in Zn complexes amounts to 2.9·10^–4. The lifetime of the lower excited (doublet) state is estimated to be 120 ± 25 nsec. We failed to reveal the luminescence of -dianions. In reducing the Pd porphyrins into -anion radicals and -dianions, a loss of the luminescent properties is observed. However, the -monoanion of phlorin in Pd octaethylporphin luminesces. The Zn complex of the phlorin anion also has the same properties. The spectral properties of Zn and Pd phlorin anions are similar: a large Stokes shift is observed at room temperature; on decrease in the temperature to 77 K the fluorescence spectrum becomes narrower, the maximum of the spectrum shifts strongly to the blue region, and the quantum yield of luminescence increases. The special features of the spectral properties of phlorin anions are explained by conformation changes in the excited state. It is found that in a solution at room temperature Pd phlorin anions quench the phosphorescence of neutral Pd porphyrins.