MODELS FOR THE PHOTOSYNTHETIC REACTION CENTER - SYNTHESIS AND STRUCTURE OF PORPHYRIN DIMERS WITH CIS-ETHENE AND TRANS-ETHENE AND SKEWED HYDROXY-METHYLENE BRIDGES

TiCl3-induced coupling of meso-formylporphyrins provides cofacial porp hyrin dimers such as 1 (M = Cu, Ni) with bridging CH = CH units. These compounds show strong interactions between the porphyrin rings; in th e case of M = Ni, the dimer can be easily transformed into the corresp onding trans isomer. Similar reactions with beta-formylporphyrins lead to a third type of dimer, a skewed hydroxymethylene-bridged bisporphy rin. These dimeric compounds are models for the photosynthetic reactio n center and should facilitate studies on the influence of the dimer g eometry on the photophysical properties.