Photochemical modeling, biomimetic

Porphyrin synthesis and functionalization based on the chemistry of Mannich bases, briefly mentioned in previous chapters, are recalled here. As far as porphyrin synthesis is concerned, studies of biomimetic models of photochemically active reaction centers are worth noting. The synthetic procedure involves amino group replacement of the pyrrole bis-Mannich base with formation of the tetrapyrrole ring of porphyrin (see 360, Chap. 11). 

The convenient triggering of selective reactions by light and the regulatory effects of light intensity variations are crucial benefits of the photochemical approach toward biomimetic model compounds. These two important aspects of biological systems, which are otherwise hardly achieved in synthetic molecular devices, will be briefly discussed in the following sections. 

The first fluorescence and fluorescence quantum yields from the excited state of the radical anion of 1,4-benzoquinone have been reported by Cook et al., and electron transfer from aromatic donors to the S state of chloranil giving the singlet radical ion pair has been observed on the fs/ps time scale (Hubig et al.). A series of porphyrin quinones having variable acceptor strengths of the quinone moiety has been synthesised by Dieks et al. and may be considered to be well-suited as biomimetic model compounds for studying photochemically-induced electron transfer in photosynthesis. 

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