Magnesium phthalocyanine

Metal-free, chloroaluminum phthalocyanine [14154-42-8] vanadyl phthalocyanine [13930-88-6], or magnesium phthalocyanines are sufficiently soluble in organic solvents and show enough bleachable absorption at 694.3 nm to serve as repeated Q-switching elements for mby lasers (qv) (180). Phthalocyanines have been used in other lasers as weU (181). 

Magnesium phthalocyanine (PcMg) can be prepared in a melt of the phthalonitrile and elemental magnesium. Often some ammonium molybdatc(VI) is added. Remaining phthalo-nitrilc and magnesium are removed by extraction with a suitable solvent and by washings with hydrochloric acid, respectively.55-83-97 136 137... 

A. Wong, R. Ida, X. Mo, Z. Gan, J. Poh and G. Wu, Solid-state Mg NMR spectroscopic and computational studies of organic compounds. Square-pyramidal magnesium(ll) ions in aqua(magnesium) phthalocyanine and chlorophyll a. ]. Phys. Chem. A, 2006,110, 10084-10090. 

O. Lumpkin, Mg and N nuclear quadrupole resonances in chlorophyll-a and magnesium phthalocyanine. /. Chem. Phys., 1975, 62, 3281-3283. 

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... 

The photosensitivity spectra of the saturated polymers containing phthalo-cyanine are shown in Fig. 49 [286]. The photosensitivity is due to the presence of the dye. The pure p form magnesium phthalocyanine has nearly the same spectra. Apparently the polymer matrix environment promotes the P-form formation. The long wavelength maximum is related to the aggregated dye form with solvent inclusion. 

Fig. 49. Photoelectromotive force spectra of the magnesium phthalocyanine in polystyrol (/), polyvinyl carbazole (2), luvican (i) [285]...

Synthesis of Magnesium Phthalocyanine from Metallic Magnesium and o-Cyanobenzamide (Classic Experiments of Linstead [2])... 

Endo A, Matsumoto S, Mizuguchi J (1999) Interpretation of the near-infrared absorption of magnesium phthalocyanine complexes in terms of exdton coupling effects. J Phys Chem A 103(41) 8193—8199... 

Beryllium metal, previously etched with acid, reacts with phthalonitrile to yield beryllium phthalocyanine, the only square planar derivative of beryllium known (10). Both anhydrous beryllium and magnesium phthalocyanines react readily with moisture to form very stable dihydrates. Dehydration may be effected only by sublimation in vacuo. Sidorov has studied the interaction of sublimed layers of beryllium and magnesium phthalocyanines with water, by infrared spectroscopy (825). Some of the absorption bands arising from the phthalocyanine unit shift when water vapor is introduced. This behavior was not noted with other phthalocyanines (see Section VI,A). 

Prepared from magnesium or magnesium oxide and o-cyanobenzamide (40), magnesium phthalocyanine has been the subject of much study since it is a synthetic analog of chlorophyll. Perhaps understandably, much of this work has been connected with photosynthesis, luminescence, fluorescence, etc. (see Section V,B). The molecular weight of magnesium phthalocyanine has been measured ebullioscopically in naphthalene (228). Because of the very low solubility of the substance, a very accurate platinum thermometer was employed. Nevertheless the successful measurement represents quite an achievement. 

In addition to water vapor, sublimed magnesium phthalocyanine also... 

Magnesium phthalocyanine may also be prepared from phthalonitrile, sodium cyanamide, and magnesium powder (107), phthalimide and magnesium (846), or phthalamide and magnesium imide (287). 

By far the most detailed thermodynamic studies have been made by Berezin, who has looked at the equilibria existing in concentrated sulfuric acid. Linstead s group were the first to observe that some of the metal phthalocyanines were demetallated in concentrated sulfuric acid, whereas others appeared indefinitely stable (10). It was shown that all phthalocyanines which resisted attack were of metals whose radii were of the right size to fit nicely into the space available at the center of the ligand. Berezin has since put these observations on a more quantitative basis (19, 21, 26). Labile complexes (i.e., those which are demetallated instantly or fairly rapidly in concentrated sulfuric acid) include those of the alkali metals, alkaline earth metals, Be, Mg, Cd, Hg, Sb(III), Pb, Sn(II), Mn(II), and Fe(III). Stable complexes (demetallated very slowly in acid) include those of Zn, Al, Cl2Sn(IV), OV(IV), Co(II), Rh(II), Os(IV), Ni(II), Pd(II), Pt(II), and Cu(II). The actual rates of decomposition vary widely thus, while calcium and magnesium phthalocyanines are demetallated very rapidly, silver and lead phthalocyanines react fairly slowly (19). The rates of decomposition in 1 M sulfuric acid increase in the sequence (19) Fe(III)... 

Putseiko (294) has observed that the addition of quinone to amorphous magnesium phthalocyanine increases the latter s photoelectric sensitivity by 102 to 103 times. The same complex deposited on a zinc oxide surface also shows enhanced sensitivity, the majority carriers now being negative (292, 848). The mechanism may involve energy transfer by excitons from the phthalocyanine to the zinc oxide surface. 

Auger techniques have also proven useful in the characterization of electrochemically induced changes in thin-film electrodes. An example concerns films (500-2000 A thick) of magnesium phthalocyanine (MgPc) deposited over a gold contact layer on a glass substrate (106) ... 

Phthalocyanines are tetrabenzotetraazaporphyrins. Copper(II) phthalocyanine 37 (Linstead 1934) is prepared from phthalonitrile and copper powder/copper(I) chloride. Magnesium phthalocyanine 38 is obtained from Mg and 2-cyanobenzamide by thermal reaction in nitrobenzene [29], the free ligand system is produced by demetalation with acid of the magnesium complex. 

Kudo, T., M. Kimura, K. Hanabusa, and H. Shirai (1998). Electrical properties of junctions between electrodeposited magnesium phthalocyanine and aluminium. Polym. J. 30(3), 177-180. 

Kobuke and colleagues described a complementary zinc porphyrin-magnesium phthalocyanine dimer that can be considered as a supramolecular switch (Figure 24). This switch is based on the variation of fluorescence induced by a change of ligands. More precisely, an imidazole-appended porphyrinatozinc-phthalocyaninatomagnesium complex was shown to spontaneously dimerize into a supramolecular short dimer (state I) in which the imidazole units are bound to the central magnesium atom of the Pcs. On addition of 2 equivalents (with respect to the dimer) of dimethyl sulfoxide (DMSO) or 1-methylimidazole to the dimer, a new extended dimer (state II) is formed in which... 

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