Synthesis and optical properties of porphyrins with exocyclic aromatic rings

Abstract

A series of meso-aryl substituted porphyrin with fused phenanthrene subunits have been synthesized to obtain insights into the influence of conjugated porphyrin systems on the electronic properties. Barton-Zard condensation of 9-nitro-phenanthrene with ethyl isocyano-acetate afforded phenanthro[9,10-c]pyrrole-1-carboxylate in good yield. Cleavage of the ester moiety with KOH in refluxing ethylene glycol gave phenanthro[9,10-c]pyrrole as a precursor of porphyrins. meso-Tetraaryltetraphenanthroporphyrin can be obtained using Lindsey condensation of phenanthro[9,10-c]pyrrole with aryl aldehyde at low temperature using boron trifluoride as catalyst. These compounds were characterized by 1H-NMR, and UV-visible spectroscopies, and MALDI-TOF mass spectrometry. The UV-visible spectra of highly conjugated porphyrins showed that ring fusion had a profound impact on the producing bathochromic shift of the Soret and Q bands into the near-infrared region. Absorption in this area is useful for wide applications in many fields including biomedicine and materials.