Synthesis and spectral properties of aromatically π-extended coumarin-fused meso-tetraphenylpyridoporphyrins

An annulative π-extension of porphyrins was accomplished by a reaction of copper(II) 2-amino-5,10,15,20-tetraphenylporphyrin with aromatic aldehydes and 4-hydroxycoumarin in the presence of a stoichiometric amount of trichloroacetic acid in o-dichlorobenzene at reflux temperature under one-pot operation. The resulting π-conjugated copper(II) coumarin-fused meso-tetraphenylpyridoporphyrins were obtained in 56–66% isolated yields after chromatographic purification and characterized on the basis of spectral data analysis. These newly constructed copper(II) coumarin-fused pyridoporphyrins underwent demetallation in the presence of sulfuric acid in chloroform to produce free-base porphyrin analogues which on zinc insertion using Zn(OAc)2 in CHCl3-MeOH afforded zinc(II) coumarin-fused meso-tetraphenylpyridoporphyrins in good yields. After structural identification, the photophysical characteristics of pyridoporphyrin macrocycles were analysed by using UV-Vis spectroscopy. The preliminary results revealed a remarkable bathochromic shift in the electronic absorption spectra of coumarin-fused meso-tetraphenylpyridoporphyrins in contrast to the non-π-extended meso-tetraphenylporphyrin macrocycles.