meso-Tetraalkynylporphyrins

Abstract

5,10,15,20-Tetra(4-n-butylphenylethynyl)porphyrin has been synthesised from 4-n-butylphenylpropynal and converted into its zinc(II) and lead(II) complexes. The solution electronic spectra of these porphyrins are compared to the analogous complexes of 5,10,15,20-tetra(trimethylsilylethynyl)porphyrin. The aryl rings of the tetra(4-n-butylphenylethynyl)porphyrin extend the porphyrin chromophore, resulting in an increase in the oscillator strength and a bathochromic shift of about 600 cm^–1 in all the absorption bands. Metallation with lead(II) results in a larger bathochromic shift of about 1400 cm^–1, when compared with zinc(II). The crystal structure of the pyridine zinc complex of 5,10,15,20-tetra(4-butylphenylethynyl)porphyrin shows that the molecule has a large approximately planar π-system. Pairs of diagonally off-set π–π stacked porphyrins pack into a layer structure. Each pyridine ligand is located in a pocket defined by four butyl chains.