Protonation-Induced Hyperporphyrin Spectra of meso-Aminophenylcorroles

Abstract

UV–vis spectrophotometric titrations have been carried out on <i>meso-</i>tris(<i>o/m/p</i>-aminophenyl)corrole (H₃[<i>o/m/p</i>-TAPC]) and <i>meso-</i>triphenylcorrole (H₃[TPC]) in dimethyl sulfoxide with methanesulfonic acid (MSA). Monoprotonation was found to result in hyperporphyrin spectra characterized by new, red-shifted, and intense Q bands. The effect was particularly dramatic for H₃[<i>p</i>-TAPC] for which the Q band red-shifted from ∼637 nm for the neutral species to 764 nm in the near-IR for H₄[<i>p</i>-TAPC]⁺. Upon further protonation, the Q band was found to blue-shift back to 687 nm. A simple explanation of the phenomena has been offered in terms of quinonoid resonance forms.