Exceptional electronic modulation of porphyrins through meso-arylethynyl groups. Electronic spectroscopy, electronic structure, and electrochemistry of [5,15-bis](aryl)ethynyl]-10,20-diphenylporphinato]zinc(II) complexes

A new class of porphyrins in which intervening ethynyl moieties connect aryl groups to the porphyrin 5- and 15-positions is described. The synthesis and optical spectroscopy of five new compounds are reported:  [5,15-bis[(4‘-dimethylaminophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), [5,15-bis[(4‘-methoxyphenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), [5,15-bis[(phenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), [5,15-bis[(4‘-fluorophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), and [5,15-bis[(4‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II). The X-ray structure of one of these complexes, [5,15-bis[(4‘-fluorophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), is unusual in that it shows the arylethynyl-phenyl rings to be coplanar with the porphyrin macrocycle. This arrangement of aryl rings with respect to the porphyrin macrocycle underscores the fact that the steric barrier to rotation between the porphyrin and arylethynyl-phenyl aromatic systems has been removed and highlights the enha...