Synthesis, Structure, and Redox and Optical Properties of 5,10,15,20-Tetraaryl-5-azaporphyrinium Salts

The fundamental properties of azaporphyrins can be modulated over a wide range by changing the number of meso-nitrogen atoms. Reported herein are the first examples of 5,10,15,20-tetraaryl-5-azaporphyrinium (MTAMAP) salts, which were prepared via metal-templated cyclization of the corresponding zinc(II) and copper(II) complexes of 10-aryl-1-chloro-19-benzoyl-5,15-dimesityl-10-azabiladiene-ac. The inclusion of one meso-nitrogen atom in the 5,10,15,20-tetraarylporphyrin skeleton considerably changes the redox and optical properties as well as the degree of aromaticity of the porphyrin ring. The present findings suggest that MTAMAP salts would be promising scaffolds for the development of new azaporphyrin-based ionic fluorophores and photosensitizers. A metal-templated annulation method is established for the synthesis of 5,10,15,20-tetraaryl-5-monoazaporphyrinium (TAMAP) salts, which exhibit characteristic redox and optical properties reflecting the electronic effects of the meso-nitrogen atom. The zinc complex of TAMAP salt generated singlet oxygen in quantum yield of 0.77 under irradiation with visible light.image

Automated summary

The properties of azaporphyrins can be modulated by changing the number of meso-nitrogen atoms. This study reports the synthesis of the first examples of 5,10,15,20-tetraaryl-5-azaporphyrinium (MTAMAP) salts. The inclusion of one meso-nitrogen atom significantly changes the properties of the porphyrin ring, making MTAMAP salts promising for the development of new fluorophores and photosensitizers.