A comparison of ortho, meta, and para substituent effects in tetraphenylporphyrins: insights into the nature of the porphyrin-phenyl electronic interaction

Abstract

Electron-withdrawing substituents on the phenyl rings of tetraphenylporphyrins exert very different electronic effects on the porphyrin core, depending on their ortho, meta, or para location. Specifically, the electronic effects of electron-withdrawing ortho substituents are remarkably small compared with those of their meta or para counterparts. This is ascribed to a large dipolar component in the porphyrin-phenyl electronic interaction and the strong orientational dependence of this polar effect.