Porphyrins photochemistry

The scientific interest in porphyrin ligands (Fig. 5) derives in part from their ability to accommodate a large series of different elements, often in various oxidation states. On the other hand porphyrins are planar molecules with a delocalized 18 Ti-electron system and a diatropic ring current [25], which makes them interesting for the design of new materials with applications in photochemistry [25-27]. 

The photochemistry of several of the iron porphyrin halocarbene complexes Fe(TPP)(=CXY) (CXY = CCF, CBr2, CCIF. CCl(CN) and the vinylidene complex Fe(TPP)=C=CAr2 (Ar = p-C6Fl4Cl) has been studied in degassed benzene... 

Andreasson, J., Kodis, G., Lin, S., Moore, A.L., Moore, T.A., Gust, Martensson, J. and Albinsson, B. (2002) The gold porphyrin first excited singlet state. Photochemistry and Photobiology, 76,... 

K. Kalyanasundaram, Photochemistry of Polypyridine and Porphyrin Complexes, Academic Press, London, 1992. 

Milanesio ME, Alvarez MG, Rivarola V, Silber JJ, Durantini EN (2005) Porphyrin-fullerene C-60 dyads with high ability to form photoinduced charge-separated state as novel sensitizers for photodynamic therapy. Photochemistry and Photobiology 81 891-897. 

During the last ten years, studies of luminescence and photochemistry of polypyridyl Ru(II), Rh(III) and Co(III) complexes, porphyrins and uranyl salts, in the presence of biological macromolecules such as DNA, have been the focus of increasing research work. The interest in such coordination compounds stems from their easily tunable properties. Not only their size and shape but also their... 

Kalyanasundaram K (1992) Photochemistry of Poly pyridine and Porphyrin complexes. Academic Press, London... 

A number of elegant transient absorption studies have shown that nickel porphyrins possess a rich and complicated excited state photochemistry (3-5). In these studies it was concluded that in basic solvents such as piperidine and pyridine the state of... 

A mechanism to account for the observed photochemistry. Based on a scheme proposed for porphyrins (16), the photooxidation of ZnPc and RuPc can be explained as follows ... 

When molecules absorb a photon and produce an electronic excited state, the energy can be dissipated in several ways luminescence, radiationless decay to the ground state, and photochemistry. Luminescence dominated the older literature because it was easy to observe. A good review of luminescence is in Volume 3 of David Dolphin s seven-volume series The Porphyrins. Picosecond laser spectroscopy allowed for exploration of the radiationless decay pathways, particularly the initial steps that compete with luminescence and lead to photochemistry. Two principal forms of radiationless decay lead to long-term metastables ligand ejection and electron transfer. 

There is a brief but eomprehensively referenced section on iron in a review of homoleptie 2,2-bipyridyl eomplexes " iron-terpy (3 pages) and iron-quaterpy (1/2 page) complexes have also been briefly reviewed." Absorption spectra and photochemistry of apprcmriate iron diimine complexes are ineluded in a text on polypyridyl and porphyrin complexes." A review of the applieation of ehiral 2,2 -bipyridines, 1,10-phenanthrolines, and 2,2 6, 2"-terpyridines in homogeneous eatalysis eontains a little material on iron complexes of such ligands." ... 

Reviews of kinetics and mechanisms deal with long-range electron transfer and with the uptake and release of dioxygen species, especially uptake from organic peroxides. " " The photochemistry of iron porphyrin complexes has been documented." ... 

KalyanasmdaTam.K. Photochemistry o/Polypyridine and Porphyrin Complexes AcademicPress London, 1992. 

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... 

II. BASIC PHOTOCHEMISTRY OF PORPHYRINS A. General Concepts and Theoretical Background... 

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. 

One example of such a course is the Haverford Laboratory in Chemical Structure and Reactivity (146) that includes six projects, each of which involves sample preparation, sample analysis and some kind of determination of the properties of the substance prepared. The projects include organopalladium chemistry, porphyrin photochemistry, enantioselective synthesis, computer-aided modeling, enzyme kinetics and electron transfer reactions. 

K. Kalyanasundaram, Photochemistry of Polypyridine and Porphyrin Complexes, Academic Press, London, 1991. (d) S. Campagna, F. Puntoriero, F. Nastasi, G. Bergamini, V. Balzani, Top. Curr. Chem. 2007, 280, 117. 

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