Synthesis of Strapped, Dimeric, and Trimeric Porphyrins Based on Intramolecular Macrocyclization Reactions

Strapped porphyrins were prepared directly by the acid-catalyzed condensation reaction of 3,3′-diethyl-4,4′-dimethyl-2,2′-dipyrrylmethane and methylenedioxy bridged dialdehydes having a strap linkage longer than 7 atoms. Dimeric and trimeric porphyrins with coplanar and orthogonal (T-shape) geometries were also synthesized in good yields as an application of this method. In the strapped porphyrins, the distortion of porphyrin ring increases systematically on shortening the strap linkage, which is confirmed by their 1H NMR data, red shifted absorption, and fluorescence spectra. In the coplanar dimeric and trimeric porphyrins, the electronic interactions between the porphyrins were distinctly observed, while in the orthogonal “T-shaped” dimers and “H-shaped” trimers, appreciable electronic interactions were not observed.