Porphyrins magnesium and

Photochemical transformations invoiving magnesium porphyrins and phthalocyanines... 

Many spectroscopic methods have been employed for the investigation of such systems For example, wide-band, time-resolved, pulsed photoacoustic spectroscopy was employed to study the electron transfer reaction between a triplet magnesium porphyrin and various quinones in polar and nonpolar solvents. Likewise, ultrafast time-resolved anisotropy experiments with [5-(l,4-benzoquinonyl)-10,15,20-triphenylpor-phyrinato]magnesium 16 showed that the photoinduced electron transfer process involving the locally-excited MgP Q state is solvent-independent, while the thermal charge recombination reaction is solvent-dependent . Recently, several examples of quinone-phtha-locyanine systems have also been reported . 

O. Dolgounitcheva et al., Ab initio electron propagator calculations on the ionization energies of free base porphyrin, magnesium porphyrin and zinc porphyrin. J. Phys. Chem. 109, 11596-11601 (2005)... 

Ichild T, Matsuo Y, Nakamura E (2013) PhotostabUity of a dyad of magnesium porphyrin and fuUerene and its appUcation to photocurrent conversion. Chem Commun 49 279-281. doi 10.1039/C2CC36988E... 

Magnesium-hydroxyl interactions have been used in the same way with a p-hydroquinone unit attached at the meso position of a magnesium porphyrin (103). Again, the evidence for oligomerization comes from 1H NMR spectroscopy, and the results can equally be interpreted as dimerization rather than polymerization. 

It may seem curious to make specific mention of this matter, but in a biological context, it is crucial. The nuclei of porphyrins and related systems are hydrophobic it appears to be generally desirable that the photosensitizer has some degree of intermediate polarity (i.e., amphiphilic properties Section 9.22.3) and the incorporation of a metal, such as zinc(II), which can take on an axial ligand (e.g., H20 in aqueous media, or RNH2 in a biological fluid), or magnesium(II), which can take on two, is expected to enhance solubility in hydroxylic solvents, and shift the... 

Crystallographic results are presented for a chlorln, a bacterlopheophorblde d, a nickel isobacteriochlorin derived from chlorophyll a, and for the cation radical of a magnesium porphyrin. 

Cation Radical Formation with Exposure of Magnesium Porphyrin Thin Films to Light and Oxygen... 

The photochemistry of true organomagnesium compounds remains almost completely unexplored. A literature search in preparation of this work found only a few scattered examples of photochemical studies, mostly in relation to Grignard reactions and 1,3-diketonate chelates Similar to the situation with organozinc compounds magnesium tetrapyrrole chelates, i.e. magnesium porphyrins 1, 5,10,15,20-tetraazaporphyrins (por-phyrazines) 2 and phthalocyanines 3 have found more interest. This is primarily related... 

Although porphyrins and especially phthalocyanines are stable compounds, both will undergo photooxidative degradation or photoexcited ET reactions . An additional problem with magnesium complexes is their low stability in aqueous solution, as they demetallate quite easily. This is one of the main reasons that many photochemical studies targeted at modeling the natural situation use the more stable zinc(II) complexes. In addition, past years have seen increasing evidence that both Mg(II) and Zn(II) chlorophylls do exist in nature. 

For example, in 1963 the photochemistry of magnesium phthalocyanine with coordinated uranium cations was studied in pyridine and ethanol and indicated the occurrence of PET to the uranium complex . A rapid photoinduced electron transfer (2-20 ps) followed by an ultrafast charge recombination was shown for various zinc and magnesium porphyrins linked to a platinum terpyridine acetylide complex . The results indicated the electronic interactions between the porphyrin subunit and the platinum complex, and underscored the potential of the linking para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance. 

The low stability of the magnesium porphyrins has precluded most potential applications. Other metallotetrapyrroles have found industrial uses for oil desulfurization, as photoconducting agents in photocopiers, deodorants, germicides, optical computer disks, semiconductor devices, photovoltaic cells, optical and electrochemical sensing, and molecular electronic materials. A few scattered examples of the use of Mg porphyrins in nonlinear optical studies have appeared" and magnesium phthalocyanines have been used in a few studies as semiconductor or photovoltaic materials" " One of the few... 

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