Tetrapyrroles photochemistry

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... 

The present article reviews the photochemical deactivation modes and properties of electronically excited metallotetrapyrroles. Of the wide variety of complexes possessing a tetrapyrrole ligand and their highly structured systems, the subject of this survey is mainly synthetic complexes of porphyrins, chlorins, corrins, phthalocyanines, and naphthalocyanines. All known types of photochemical reactions of excited metallotetrapyrroles are classified. As criteria for the classification, both the nature of the primary photochemical step and the net overall chemical change, are taken. Each of the classes is exemplified by several recent results, and discussed. The data on exciplex and excimer formation processes involving excited metallotetrapyrroles are included. Various branches of practical utilization of the photochemical and photophysical properties of tetrapyrrole complexes are shown. Motives for further development and perspectives in photochemistry of metallotetrapyrroles are evaluated. 

Even a short glance at the chemical literature is sufficient to get an impression (and it is not only an impression but a reality) that during the two last decades, the photochemistry of tetrapyrrole complexes belongs to the fastest developing areas in the field of excited-state chemistry of coordination com-... 

Turning back to the definition of photochemistry and anticipating the classification of photochemical reactions of metallotetrapyrroles, it should be kept in mind that a true photochemical process is only that involving an electronically excited particle (in this review it means an excited tetrapyrrole complex). All subsequent reactions are spontaneous (in photochemistry they are familiarly called dark reactions). Exactly speaking, each classification of photochemical reactions should start with an answer to the question what is the nature of the primary photochemical step involving a complex in its photochemically reactive excited state It must be admitted that for the... 

In chemistry, however, the term isomers is generally used in connection with isolable compounds. Keeping this limitation in mind it has been found that, apart from chemistry and photochemistry of common inorganic complexes [1], isomerism is a very rare phenomenon in the chemistry of tetrapyrrole complexes. 

Discussion of photochemical properties of natural and artificial photosynthetic centers is beyond the scope of this chapter. This part of photochemistry of tetrapyrrole complexes involving systems seems to be the most elegant part in the field and one of the most exciting parts in photochemistry and photobiology as a whole. 

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