Studien zur Synthese von cofacialen Chlorindimeren zur Untersuchung des Symmetrie-Einflusses auf den lichtinduzierten Elektronentransfer

Abstract

Porphyrin derivatives play an important role in respiration and photosynthesis. Structural investigations of bacterial and plant photosynthetic reaction centers demonstrated that the so called special pair consisting of two chlorophyll derivatives is the starting point for light induced electron transfer of photosynthesis. The chlorophylls of the special pair are more or less arranged in cofacial fashion with an interplanar distance of about 3.4Å.:br:Several cofacial porphyrin dimers were prepared to mimic the special pair and to elucidate its specific function. Porphyrin based special pair mimics allow to study influence of distance and of deviation from an ideal parallel orientation of the monomeric subunits. Another important feature namely influence of the symmetry cannot be addressed with cofacial porphyrin dimers due to their high D:sub:4:/sub:h symmetry of the porphyrin core which allows only one cofacial assembly.:br:In contrast chlorins and bacteriochlorins possess lower C:sub:2:/sub:v or D:sub:2:/sub:h symmetry respectively. Therefore cofacial chlorins dimers form two arrangements of different symmetry. One cofacial chlorin dimer has the saturated rings of the chlorin units trans the other one cis orientated. Strategies for syntheses of appropriate cofacial chlorin dimers are reported.