Paramagnetic metalloporphyrins

Another concern specific to the use of porphyrin-based photosensitizers is the fact that singlet state lifetimes are usually less than 10 ns and photosensitization occurs mostly from the triplet state. This requires the selection of systems that efficiently generate triplet states, which is not the case of paramagnetic metalloporphyrins. 

Paramagnetic Metalloporphyrin Cation Radicals and Their Magnetic Properties. .. 172... 

Zr(IV), and Ce(IV) as the central metal ion. Copper(II) porphyrins are among the most studied of the paramagnetic metalloporphyrins. The Cu(II) complexes show a low-temperature luminescence that arises from the and states that exist in thermal equilibrium. These two states are derived from the lowest excited triplet state on the porphyrin ring, which is split because of the presence of a unpaired electron on the Cu(II) center. Transient absorption measurements show that the ambient temperature excited-state decay times are lowered when a ligand is associated with the axial coordination positions of the tetracoordinate Cu(Il) porphyrin complex. The excited state lifetimes of Cu(II) porphyrin complexes in solution can be either dependent or independent of the temperature and solvent. For the octaethylporphyrin complex Cu(OEP) the excited state lifetime increases as the temperature is lowered, and also as the solvent polarity is increased. By contrast, the excited state lifetime of the tetraphenylporphyrin Cu(TPP) is insensitive to both the temperature and the polarity of the solvent. This difference in their photophysical behavior is likely due to a difference in the energy gap between the charge transfer state and the T/ T states in the pair of complexes. 

Mao JH, Zhang Y, Oldfield E (2002) Nuclear magnetic resonance shifts in paramagnetic metalloporphyrins and metalloproteins. J Am Chem Soc 124 13911-13920... 

Polymers that contain paramagnetic ions are classified into two categories (1) polymers with paramagnetic metalloporphyrins as side chains, and (2) polymers containing paramagnetic metal ions in the main chain. 

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